Performing Gas Engine Tune Up

COMPETENCY BASED LEARNING MATERIAL

Sector:

AUTOMOTIVE

Qualifications:

Automotive Servicing NC I

Unit of Competency:

Perform Gas Engine Tune Up

Module Title:

PERFORMING GAS ENGINE TUNE UP

Technical Education and Skills Development Authority

TESDA Complex, East Service Road, South Superhighway, Taguig, Metro Manila

NATIONAL CERTIFICATE LEVEL 1

QUALIFICATION LEVEL

COMPETENCY-BASED LEARNING MATERIALS

No. Basic Competencies Module Title Code
1. Receive and Respond to 1. Receiving and Responding to 500311101

Workplace Communication Workplace Communication 500311102
2. Work with Others 2. Working with Others 500311103
3. Demonstrate Work Values 3. Demonstrating Work Values 500311104

4. Practice Housekeeping 4. Practicing Housekeeping
Procedures Procedures

No. Common Competencies Module Title Code
1. Apply Appropriate 1. Applying Appropriate ALT723201
ALT723202
Sealant/Adhesive Sealant/Adhesive ALT311201
2. Move and Position Vehicle 2. Moving and Positioning ALT311202

3. Perform Housekeeping Vehicle ALT311203
4. Perform Mensuration and 3. Performing Housekeeping ALT723203

Calculation 4. Performing Mensuration and ALT723204
5. Perform Safety Practices Calculation
6 Read, Interpret and Apply ALT723205
5. Performing Safety Practices
Specifications and Manual
6. Reading, Interpreting and
7. Use and Apply Lubricant/Coolant Applying Specifications and
Manual
8. Perform Shop Maintenance
7. Using and Applying Lubricants/
Coolants

8. Perform Shop Maintenance

No. Core Competencies Module Title Code
ALT723301
1. Perform Diesel Engine Tune Up 1. Performing Diesel Engine
ALT723302
Tune Up
ALT723303
2. Perform Gas Engine Tune 2. Performing Gas Engine ALT723304
ALT723305
Up Tune Up
ALT723306
3. Service Automotive Battery 3. Servicing Automotive Battery

4. Service Ignition System 4. Servicing Ignition System

5. Test and Repair Wiring/Lighting 5. Testing and Repairing Wiring/

System Lighting System

6. Perform Underchassis Preventive 6. Performing Underchassis

Maintenance Preventive Maintenance

How to use this Competency-Based Learning Material

Welcome to the module “Performing Gas Engine Tune Up”. This module contains
training materials and activities for you to complete.

The unit of competency "Perform Gas Engine Tune Up" contains the knowledge,
skills and attitudes required for Automotive Servicing. It is one of the specialized modules
at National Certificate level I (NC I).

You are required to go through a series of learning activities in order to complete
each learning outcomes of the module. In each learning outcome there are Instruction
Sheets to help you better understand the required activities. Follow these activities on your
own and answer the self-check at the end of each learning outcome. You may remove a
blank answer sheet at the end of each module (or get one from your facilitator/trainer) to
write your answers for each self-check. If you have questions, don’t hesitate to ask your
facilitator for assistance.

Instruction sheets:

• Information Sheet - This will provide you with information (concepts,
principles and other relevant information) needed in

performing certain activities.

• Operation Sheet - This will guide you in performing single task, operation or
process in a job.

• Job Sheet - This is designed to guide you how to do a job that will
contribute to the attainment of the learning outcome.

• Assignment Sheet - The assignment sheet is a guide used to enhance (follow-
up) what you have learned in the information sheet,

operation sheet or job sheet.

• Worksheet - Worksheets are the different forms that you need to fill-up
in certain activities that you performed.

Recognition of Prior Learning (RPL)

You may already have some or most of the knowledge and skills covered in this
learner's guide because you have:

• been working for some time
• already completed training in this area.

If you can demonstrate to your trainer that you are competent in a particular outcome,
you don't have to do the same training again.

Talk to your trainer about having them formally recognized. If you have a qualification
or Certificate of Competence from previous training, show it to your trainer. If the skills you
acquired are still current and relevant to the unit/s of competency they may become part of
the evidence you can present for RPL. If you are not sure about the currency of your skills,
discuss this with your trainer.

After completing this module ask your trainer to assess your competency. Result of
your assessment will be recorded in your competency profile. All the learning activities are
designed for you to complete at your own pace.

Inside this learner's guide you will find the activities for you to complete and at the
back are the relevant information sheets for each learning outcome. Each learning outcome
may have more than one learning activities.

At the back of this learner's guide is a Learner Diary. Use this diary to record
important dates, jobs undertaken and other workplace events that will assist you in providing
further details to your trainer or an assessor. A Record of Achievement is also provided for
your trainer to complete once you complete the module.

Program /Course Automotive Servicing NC I
Unit of Competency Perform Gas Engine Tune Up

Module Performing Gas Engine Tune Up

INTRODUCTION:

The purpose of a gasoline engine is to convert gasoline into motion so that the
vehicle can move. Currently the easiest way to create motion from gasoline is to burn
the gasoline inside an engine. Therefore, an engine is an internal combustion engine
-- combustion takes place internally.

In this module you will identify gasoline engine troubles and perform tune up. You
will be performing activities to develop your skill in checking/adjusting valve clearance;
inspecting/testing and replacing spark plugs; checking/replacing fuel filter and air
cleaner; inspecting/replacing contact point condenser; testing/adjusting dwell angle and
ignition setting; adjusting engine idle speed and mixture; checking advance mechanism
and adjusting ignition timing; and conducting compression test.

You will also review underpinning knowledge such as types of lubricants and fluids;
automotive systems; equipment safety requirements; relevant company policies;
personal safety requirements; manual handling techniques; cleaning method and
materials; principle of engine operation; servicing inspection checklist; and Positive work
values (honesty, perseverance, attention to details).

After doing the learning activities in this module you will be assessed by your
instructor on tuning up gasoline engine.

LEARNING OUTCOMES

Upon completion of this module you should be able to:

1. Identify and explain the functions of tune-up equipment and enumerate the major
steps in tuning-up an engine;

2. Measure/adjust valve tappet clearance;
3. Test spark plug;
4. Check/replace fuel and air filter;
5. Test and replace ignition breaker;
6. Check and adjust distributor setting;
7. Set fuel mixture and idle rpm; and
8. Perform compression testing.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 1

PERFORMANCE CRITERIA

All standard of performance for Performing Gasoline Engine Tune Up is in
accordance with company standard operating procedure and manufacturer’s
specification Manuals using specified tools and equipment.

1. Identify and explain the functions of tune-up equipment and enumerate the major
steps in tuning-up an engine:
1.1 Functions of tune-up equipment are identified and explained
1.2 Major steps in tuning-up and engine are enumerated

2. Measure/adjust valve tappet clearance:
2.1 Valve tappet clearance is set
2.2. Checking and adjustment is performed

3. Test spark plug:
3.1. Spark plug clearance is adjusted.
3.2. Spark plug is tested.
3.3. Spark plug test result analyzed and appropriate recommendations are
prescribed.

4. Check/replace fuel filter and air cleaner:
4.1. Fuel filter and air cleaner are replaced.
4.2. Fuel filter is free of sediments and impurities.

5. Test and replace ignition breaker:
5.1. Ignition breaker is tested and replaced
5.2. Condenser is tested and replaced

6. Check/adjust ignition distributor setting:
6.1. Ignition distributor is checked
6.2 Ignition distributor setting is adjusted

7. Set fuel mixture and idle rpm:
7.1. Fuel mixture and idle rpm is adjusted
7.2. Advanced timing is checked

8. Perform compression test:
8.1. Compression test is performed.
8.2. Compression test result is interpreted and appropriates recommendations is
prescribed.

PREREQUISITES

To complete this module you must have completed the following modules:

- Performing Housekeeping
- Performing Mensuration and Calculation
- Performing Safety Practices
- Reading, Interpreting and Applying Specifications and Manual
- Using and Applying Lubricants/ Coolants
- Perform Shop Maintenance

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 2

QUALIFICATION : Automotive Servicing NC I

UNIT OF COMPETENCY : Perform Gas Engine Tune Up

MODULE TITLE : Performing Gas Engine Tune Up

LEARNING OUTCOME 1 : Identify and explain the functions of tune-up equipment
and enumerate the major steps in tuning-up an engine.

ASSESSMENT CRITERIA:
1. Functions of tune-up equipment are identified and explained.
2. Major steps in tuning-up an engine are enumerated.

RESOURCES:

1. Auto Mechanics 10th Edition,
by: William H. Crouse and Donald L. Anglin

2. Video CD on Gas Engine Tune-up

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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LEARNING EXPERIENCES

Learning Outcome # 1: Identify and explain the functions of tune-up equipment
and enumerate the major steps in tuning-up an engine.

Learning Activities Special Instructions

1. Read the information on engine • Study the function of the various

testing equipment or view the video on equipment described in the

engine tune-up. Information Sheet “Identifying Engine

Testing Equipment”

2. Answer the self-check provided.

3. Compare your answers to the answer
key.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 4

LO1 - IDENTIFY AND EXPLAIN THE FUNCTIONS OF TUNE-UP
EQUIPMENT AND ENUMERATE THE MAJOR STEPS IN
TUNING-UP AN ENGINE

LEARNING OUTCOME:

At the end of this learning activity you should be able to identify and explain the
functions of tune-up equipment and enumerate the major steps in tuning-up an engine.

EQUIPMENT AND MATERIALS:

• Service manual
• Video on gas engine tune-up
• Computer or video player with monitor

LEARNING ACTIVITIES:

Activity # 1: Identify and explain the functions of tune-up equipment and
enumerate the major steps in tuning-up an engine

a. Read the Information Sheet LO1-1. “Overview of Internal Combustion
Engine”.

b. Read the Information Sheet LO1-2. “Identifying Engine Testing Equipment”.

c. Ask your instructor to show you the actual engine testing equipment in order
to become familiar with its appearance and features.

d. Study the vacuum gauge readings in Figure 8 and their corresponding
diagnosis to solve engine problems.

e. Read the “Typical Tune-up Procedure” on pages 17 to 18 and discuss it with
your instructor.

f. Answer Self-Check LO1-1. Compare your answers using the answer key

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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Information Sheet LO1-1: Overview of Internal Combustion Engine

Internal Combustion Engines

An engine is a machine that converts heat
energy into mechanical energy. The heat
from burning a fuel produces power which
moves the vehicle. Sometimes the engine
is called the power plant.

Automotive engines are internal-
combustion (IC) engines because the fuel
that runs them is burned internally, or
inside the engines. Reciprocating means
moving up and down, or back and forth.
Most automotive engines are reciprocating.
They have pistons that move up and down,
or reciprocate, in cylinders. These are
piston engines.

Rotary engines have rotors that spin or
rotate. The only such engine now used in
automobiles is the Wankel engine.

Figure LO1-1.1 An inline four-cylinder spark ignition
engine with overhead camshaft. (Chrysler
Corporation)

Two Kinds of Piston Engines

The two kinds of piston engines are the
spark-ignition engine (gas) and the
compression-ignition (diesel) engine. The
differences between them are:
• The type of fuel used
• The way the fuel gets into the cylinders
• The way the fuel is ignited

Figure LO1-1.2 The two limiting positions of the piston
are the top dead center and bottom dead center. A

piston stroke occurs when the piston moves from BDC
to TDC or vise versa.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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Carburetor-Type Engine

The fuel system mixes gasoline or similar
fuel with air to make a mixture that will burn
in the engine cylinders. Some fuel systems
use a carburetor. It sits on top of the
engine intake manifold. The carburetor
mixes the air and fuel into a combustible
mixture.

Figure LO1-1.3 The carburetor sits on top of the
engine intake manifold.

Electronic Fuel Injected Engine

Engine models from 1985 and later have
electronic fuel injectors (EFI). An electronic
control module (ECM) or computer controls
one or more fuel injectors. When the
engine needs fuel, a signal from the ECM
opens the injector. Fuel then sprays into
the air on its way to the engine cylinders.
This provides the air-fuel mixture the
engine needs for combustion.

Engine Construction Figure LO1-1.4 The basic parts of a fuel system, with
a fuel injector located in the intake port of each
In a four-cylinder spark-ignition engine, cylinder.
each cylinder is about 4 inches (102 mm)
in diameter. The cylinder head covers the Figure LO1-1.5 Three views that show the actions in
top of the cylinder. The bottom of the an engine cylinder. (A) The piston is a metal plug that
cylinder is open. As the engine runs, the
pistons slide up and down in the cylinders. fits snugly into the cylinder. (B) When the piston is
In (A), the piston is at its lower limit of pushed up into the cylinder, air-fuel mixture is trapped
travel, or BDC. The space above the piston and compressed. (C) When the compressed air-fuel
is filled with air-fuel mixture (about 14.7
parts air and 1 part gasoline). Next (B), the mixture is ignited by a spark at the spark plug, the
piston moves up the cylinder toward TDC. high pressure pushes the piston down in the cylinder.
This compresses the mixture. As the piston
nears TDC, an electric spark ignites the
mixture (C). The mixture burns creating
high temperature and a resulting pressure
that pushes the piston down the cylinder.
This downward movement produces the
power that moves the vehicle. The actions
are the same in all cylinders and continue a
s long as the engine runs.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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Pistons and Piston Rings

Pistons are made of aluminum alloy
(aluminum mixed with other metals). They
weight about 1 pound (0.454 kg). The
piston is slightly smaller than the cylinder,
which allows the piston to slide up and
down. This is a sliding fit.

There is a small gap or piston clearance
between the piston and the cylinder wall.
This gap must be closed. Otherwise, some
of the compressed air-fuel mixture leaks
past the pistons and into the crankcase.
This leakage is blowby. Excessive blowby
reduces engine power, wastes fuel, and
pollutes the air.

To prevent excessive blowby, piston rings
are installed on the pistons. The rings are
split at one point. This allows them to be
expanded slightly, slipped over the head of
the piston, and into ring grooves cut into
the piston.

There are two types of piston rings: Figure LO1-1.6 Piston and piston rings. Top, rings
1. Compression rings -- form a sliding seal separated and above the piston. Bottom, piston rings
installed in grooves in the piston. Piston is attached to
between the piston and the cylinder the connecting rod by the piston pin. Only the upper
wall.
2. Oil-control rings (or oil rings) – scrape part of the connecting rod is shown.
off most of the lubricating oil splashed
on the cylinder wall, and return the oil
into the crankcase.

Figure LO1-1.7 Compressed air-fuel mixture “blow by”
past the piston.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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Reciprocating to Rotary Motion

The reciprocating motion of the piston must Figure LO1-1.8 Piston-and-connecting-rod assembly.
be changed to rotary motion to turn the
drive wheels. A connecting rod and a crank
on the crankshaft make this conversion.
The connecting rod connects to the piston
pin in the piston to a connecting-rod
journal, or crankpin, on the crankshaft. It
swings in a circle as the crankshaft rotates.
A rod cap and bolt attach the connecting
rod to the connecting-rod journal. They
hold a split bearing (two-halves), or
connecting-rod bearing in place in the cap
and rod. A slight clearance allows the
connecting-rod journal to turn inside the
bearing. The clearance is normally filled
with oil to prevent metal-to-metal contact.

Engine Valves

Most engines have two holes, or ports in the upper enclosed end of the cylinders. (Some
engines have more than two ports.) One port is the intake port. The other is the exhaust
port. The two ports are open only part of the time. The rest of the time they are closed by
the intake and exhaust valves. The valves are plugs with long stems that open and close
the ports in the cylinder head. When an valve moves up into its port, the valve seals tightly
against a valve seat. In this position, the valve is closed, sealing the port. When a valve is
pushed down off its seat, the port is open. Then the air-fuel mixture or exhaust gas can
pass through the port. The opening and closing of the valves are controlled by the valve
train.

Figure LO1-1.9 The four piston strokes. (A) Intake stroke. The intake valve (at left) has opened. The piston is
moving downward, allowing the air-fuel mixture to enter the cylinder. (B) Compression stroke. The intake
valve has closed. The piston is moving upward, compressing the mixture. (C) Power stroke. The ignition

system has delivered a spark to the spark plug that ignites the compressed mixture. As the mixture burns, it
creates a high pressure that pushes the piston down. (D) Exhaust stroke. The exhaust valve has opened. The

piston moves upward as the burned gases escape from the cylinder.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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Valve Action

In many engines, each cylinder has two Figure LO1-1.10 Camshaft and bearing removed from
valves. One for intake and the other for an overhead valve V-8 engine.
exhaust. Some engines have more than
two valves. These are multivalve engines.
They have three, four, five or six valves per
cylinder. For example, an engine with four
valves in each cylinder in a four-valve
engine.

The valve train is the series of parts that
open and close the valves. The action
starts at the camshaft.

The crankshaft drives the camshaft through
gears, sprockets and chain, or sprockets
and a toothed timing belt. Most camshafts
have a cam for each valve in the engine.
Each cam is a round collar with a high spot
or lobe.

The camshaft mounts overhead, on top of
the cylinder head. The bucket tappet sits
on top of the valve stem. Underneath the
tappet is a valve spring that holds the
tappet up against the cam. When the
rotating cam brings the cam lobe down
against the top of the bucket tappet, the
lobe pushes the tappet down off its seat.
The valve opens. As the cam continues to
rotate, the lobe moves away from the
tappet. The spring pushes the tappet and
valve up until the valve seats.

Multiple-Cylinder Engine

A single-cylinder four-cycle engine has only
one power stroke every two crankshaft
revolutions. The engine delivers power only
one-fourth of its running time. This is during
the power stroke. During the other three
strokes the piston is not delivering power to
the crankshaft.

For a more even flow of power, automotive

engines are multiple cylinder engines. They

have three or more cylinders. In general, Figure LO1-1.11 Operation of a cam on an overhead-
the more cylinders in an engine, the camshaft engine as the camshaft rotates. Top, the
smoother it runs. With six or more
cylinders, the power impulses follow each cam lobe is away from the bucket tappet and the valve
is closed. Bottom, the cam lobe is pushing the tappet

and valve down, opening the valve

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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so closely that they overlap. The more
even power flow results in a smoother
running engine.

Flywheel and Drive Plate

Even when the power impulses overlap, the flow of power from the pistons to the
crankshaft is not smooth. Each power stroke delivers a sudden power impulse to the
crankshaft. This causes the crankshaft to try to speed up. During the other three piston
strokes, the crankshaft tries to slow down. A weight on each end of the crankshaft, a
damper on the front and a flywheel on the rear helps keep it running smoothly.

Figure LO1-1.12 Crankshaft and related parts for an inline six-cylinder engine. The flywheel is to the right.
(Ford Motor Company)

On vehicles with a manual transmission, the heavy metal flywheel helps smooth out the
power flow. It resists any sudden change in the crankshaft’s speed of rotation. Vehicles
with an automatic transmission or transaxle have a light drive plate (or flex plate) with a
fluid-filled torque converter attached to the crankshaft. This acts the same way as the
flywheel to smooth the power flow. The flywheel also serves as the driving member of the
clutch in cars with a manual transmission. In addition, the flywheel (and also the drive plate)
has a ring of teeth on its outer rim. A small pinion gear on the starting motor meshes with
these ring-gear teeth when the starting motor operates. This rotates the flywheel and
crankshaft to start the engine.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 11

Information Sheet LO1-2: Identifying Engine Testing Equipment

Quick and accurate diagnosis and service of the engine require the use of various test
instruments and gauges. These will show if the battery, starting, charging, fuel ignition and
emissions systems are operating properly. They would also indicate the mechanical
condition of the engine.

1. Tachometer – Electric or optical tachometers
are used in the shop. The electric tachometer
connects to the engine primary circuit. The
tach counts the number of times per second
the primary circuit opens and closes. The
optical tachometer has a light beam focused
on a rotating part such as the engine
crankshaft pulley. The tach counts how many
times per second a mark on the pulley passes
by.

(A) INSTRUMENT-PANEL TACHOMETER
The magnetic tachometer is usually combined with the magnetic timing tester. It uses a probe
inserted in the engine probe hole. The probe reacts to a mark on the crankshaft pulley or to a
pulse ring or location indicator on the crankshaft. On an engine with electronic engine control
system (EEC), engine-speed data is available through the diagnostic connector. A scan tool or a
computerized engine analyzer can display the rpm.

2. Dwellmeter – The dwellmeter electrically (B) SHOP TACHOMETER (DWELL-TACH)
measures how long the contact points
remaing closed during each ignition cycle of a Figure LO1-2.1 Instrument-panel and shop
contact-point ignition system. The average for tachometers that measures crankshaft
all cylinders is then displayed in degrees of speed or engine rpm.
distributor-cam rotation. The technican can
also use the dwellmeter to set contact-point
gap and to check for unwanted dwell variation
as engine speed increases. Excessive
variation indicates mechanical trouble in the
distributor.

In electronic ignition systems, the ECM
controls dwell. It is not adjustable. The
dwellmeter is used to check the duty cycle of
the mixture-control solenoid in a feedback
carburetor.

A dwell-tach meter is a single meter that Figure LO1-2.2 Dwellmeter showing the
serves as both a dwellmeter and a scales for eight, six and four cylinder
tachometer. This is possible because both engines (Sun Electric Corporation).
meters have two leads and require the same
connections. Pushing a button or turning a
knob on the meter switches the reading from
rpm to dwell.

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3. Cylinder Compression Tester – The cylinder Figure LO1-2.3 Using a cylinder
compression tester measures the ability of the compression tester. (Toyota Motor Sales,
cylinders to hold compression while the
starting motor cranks the engine. The USA, Inc.)
compression tester is a pressure gauge that
measures the amount of pressure or
compression, built-up in the cylinder during
the compression stroke. How well a cylinder
holds compression is an indication of the
condition of the piston, piston rings, cylinder
wall, valves and head gasket.

The spark plugs must be removed to use the compression tester. Before removing the
spark plugs, be sure the engine is at normal operating temperature and the battery is fully
charged. Use compressed air to blow any dirt out of the spark-plug wells. Another way is to
disconnect the cables, loosen the spark plugs about one turn and reconnect the cables.
Then start the engine. Run the engine for a few seconds at 1000 rpm. The leaking
combustion gases will blow the dirt out of the plug wells.

Remove the spark plugs. Block the throttle wide-open so the maximum amount of air enters
the cylinders. Thread the compression-tester adapter into the spark-plug hole of number 1
cylinder. Disable the ignition to prevent coil damage from high-voltage arcing.

Note: Different steps are necessary to disable various ignition systems. On many engines with a
separate ignition coil, disconnect the primary lead from the negative terminal of the coil.
Some General Motor engines have high-energy ignition (HEI) with the coil in the cap.
Disable these by disconnecting the larger red wire from the distributor. To disable a
distributorless ignition system, disconnect the wiring-harness connector between the ECM
and the ignition module.

Disable the electric fuel pump. Operate the starting motor to crank the engine through
four compression strokes (eight crankshaft revolutions). The needle on the compression
gauge will move around to show the maximum pressure in the cylinder. Write down this
figure. Then test the other cylinders.

Engine compression reading are usually considered normal if the lowest reading is 75
percent or more of the highest. For example, if one cylinder in an engine has a
compression pressure of 120 psi (828 kPa), then all cylinders should have compression
readings of 90 psi (621 kPa) or higher. Typical compression pressures vary among
engines and manufacturers. In many General Motors engines, no cylinder should have
a compression pressure of less than 100 psi (690 kPa). Toyota specifies a maximum
compression pressure of 142 psi (990 kPa) in some engines. The following section
describes interpreting the results of the compression test.

Results of Compression Test

Engine compression readings are usually considered normal if the lowest reading is 75
percent or more of the highest. For example, if one cylinder in an engine has a
compression pressure of 120 psi (828 kPa), then all cylinders should have compression
readings of 90 psi (621 kPa) or higher. Typical compression pressures vary among
engines and manufacturers. In many General Motors engines, no cylinder should have

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a compression pressure of less than 100 psi (690 kPa). Toyota specifies a maximum
compression pressure of 142 psi (990 kPa) in some engines. The following section
describes interpreting the results of the compression test.

The manufacturer’s specification show what the compression pressures should be. If
compression is low, there is leakage past the piston rings, valves or cylinder-head
gasket. If the readings vary, how they vary may indicate the cause of the problem.

A Compression test made as described in Figure 4 is a dry compression test. In a
spark-ignition engine, a second or wet compression test will help locate the leak. Squirt
about 1 tablespoon [15 cc] of engine oil through the spark-plug hole into the cylinder.
Recheck the compression.

Caution: Never perform a wet compression test on a diesel engine. The heat of a compression could
ignite the oil and damage the compression tester. Also, since the oil is not compressible, it could
fill the combustion chamber and create a hydrostatic lock. This prevents the crankshaft from
turning and may damage the engine.

If the compression pressure increases Compression Gauge Possible Engine
to a more normal value, the low
compression probably is due to Reading Condition
leakage past worn piston rings.
Adding oil helps seal the rings Fails to climb during Valve sticking open
temporarily as the cylinder holds
compression better. Other possible all compression
causes are a worn piston or cylinder
wall, and rings that are broken or strokes
stuck in their piston-ring grooves.
20 PSI (138 kPa) Faulty rings or valve
If adding oil does not increase
compression pressure, the leakage below normal seating
may be past the valves. Possible
causes include: More than 20 PSI (138 Faulty head gasket

kPa) below normal in

two cylinders next to

each other

20 PSI (138 kPa) Excessive carbon

above normal buildup in

combustion

chamber

Figure LO1-2.4 Compression-gauge readings and

the probable engine conditions. (Ford Motor

Company)

1. Broken valve springs
2. Incorrect valve adjustment
3. Sticking valves, valves not seating
4. Worn or burned valves
5. Worn or burned valve seats
6. Worn camshaft lobes
7. Dished or worn valve lifters

A blown head gasket also causes a low reading during a wet compression test. The
gasket has burned away and compression pressure leaks between the cylinder block
and head. Low or no compression in two adjacent cylinders is probably due to a blown
head gasket between the two cylinders.
Whatever the cause—rings, pistons, cylinder walls, valves, gaskets—the cylinder head
must be removed to correct the trouble. The exception is an improper valve adjustment
that holds the valves slightly off their seats. Valves are adjusted with the cylinder head
in place.

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ALT723302 March 4, 2006 14

4. Cylinder Leakage Tester – The cylinder
leakage tester checks compression but in
a different way. It applies air pressure to
the cylinder with the piston at TDC on the
compression stroke. In this position, the
engine valves are closed. Very little air
should escape from the cylinder if the
engine is in good condition.

To use the cylinder leakage tester:

a. Remove all spark plugs.

b. Disconnect the air cleaner.

c. Remove the oil-filter cap or dipstick. Figure LO1-2.5 Cylinder leakage tester. The
d. Remove the radiator cap and fill the whistle is used to locate TDC in number 1
cylinder. (Sun Electric Corporation)
radiator to the proper level.

e. Block the throttle-wide-open.

f. Connect the adapter, with the whistle, to the spark plug hole of number 1 cylinder.

g. Crank the engine until the whistle sounds. This means number 1 piston is moving up

on the compression stroke.

h. Continue rotating the crankshaft until the TDC timing marks align.

i. Then disconnect the whistle from the adapter hose and connect the tester.

j. Apply air pressure into the cylinder. Note the gauge reading, which shows the

percentage of air leaking from the cylinder. Specifications vary, but a reading of

above 20 percent means excessive leakage.

k. Listen at the air intake, tail pipe, and oil-filter hole. If air blows-out of an adjoining

spark-plug hole, the head gasket is blown between the cylinders. If air bubbles up

through the radiator, the trouble is a blown head gasket or a cracked cylinder block

or head. Any of these conditions may allow leakage from the cylinder into the cooling

system.

l. Check the other cylinders in the same way.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 15

5. Engine Vacuum Gauge – The engine
vacuum gauge measures intake-manifold
vacuum. The intake-manifold vacuum
changes with the load on engine defects.
The way the vacuum varies from normal
indicates what could be wrong inside the
engine. Before making the test, check
that all vacuum hoses are properly
connected and not leaking. Make a
backpressure test if a restricted exhaust
system is indicated.

Connect the vacuum gauge to the intake
manifold. Start the engine and run it until
it reaches normal operating temperature.
Then note the vacuum reading at idle and
other speeds, as described below. Figure
8 shows the meaning of various vacuum-
gauge readings. Common vacuum-gauge
readings are described below.

Figure LO1-2.6 The cylinder-leakage tester applies
air pressure to the cylinder through the spark-plug
hole with the piston at TDC and the valves-closed.
Places where air is leaking can then be located.

(Sun Electric Corporation)

a. A steady and fairly high reading on Figure Lo1-2.7 The vacuum gauge connected to
idle indicates normal performance. intake manifold to measure intake-manifold vacuum.
Specifications vary with different
engines. A reading between 17 and (Toyota Motor Sales USA, Inc.)
22 inches (432 and 599 mm) of
mercury usually indicates normal
engine operation. The reading will be
lower at higher altitudes because of
lower atmospheric pressure. For
every 1000 feet [305 m] above sea
level, the reading is reduced about 1
inch (25.4 mm] of mercury (Hg).

Note: Inches or millimeters of mercury refers to the way the vacuum is measured. There is no

mercury in the gauge. The readings compare with the changes that a vacuum would

produce on a column of mercury in a barometer. Figure 9 shows the relationship among

the various measurements of vacuum and pressure.

Reading Diagnosis

b. A steady and low reading on idle Average and Everything is
indicates less ignition or valve steady at 17- normal.
timing, or possibly leakage past the
piston rings. This excessive blowby 22.
could be due to worn or stuck piston

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 16

rings, or worn cylinder walls or Extremely low Air leak at the
pistons. Any of these reduces reading— intake
engine power. With less power, the
engine does not develop or “pull” as needle holds manifold or
much vacuum. steady. throttle body;
c. A steady and very low reading on
idle indicates the air leak at the Needle incorrect
intake manifold or throttle body. The fluctuating timing.
leak could be around the throttle between high Idle mixture
shaft. Air leakage into the intake needs
manifold reduces vacuum and and low adjustment,
engine power. Incorrect timing may reading. spark-plug
also cause this condition. gap too
Needle narrow,
Note: Some engines with high-lift cams and fluctuates very valves
longer valve overlap have a lower and more sticking open.
uneven intake manifold vacuum. Also, some slowly, Idle mixture
emission-control systems lower intake-manifold ranging 4 or 5 needle
vacuum. adjustment,
points. spark-plug
d. A reading that varies rapidly— gap too
increasing with engine speed— Needle narrow,
between 10 and 22 inches (254 and fluctuating valves
599 mm) indicates a weak or broken rapidly at sticking open.
valve spring. idle—steadies
as RPM is Worn valve
e. A reading that drops back to zero as increased guides
engine speed increases indicates a Needle drops
restricted exhaust system. to low reading, Burned or
resume to leaking
f. Regular dropping back of the needle normal , drops valves.
indicates a valve that is burned or back, etc., at a
sticking open, or a spark plug not
firing. regular
interval.
g. Irregular dropping back of the
needle indicates valves that are Needle drops Restricted
sticking open only part of the time. to zero as exhaust
system.
h. Floating motion or slow back-and- engine RPM is
forth movement of the needle increased.
indicates that the air-fuel mixture is
too rich. Needle holds Late ignition
steady at 12 to or valve
On some engines, a vacuum-gauge quick 16—drops to 0 timing,
test can be made fro loss of compression
due to leakage around the piston. This and back to leaking piston
would result from worn piston rings, about 21 as rings. Check
pistons, or cylinder walls. Race the engine
and then quickly release the throttle. The throttle is with
needle should swing around to 23 to 25 opened and compression
inches (584 to 635 mm) as the throttle
closes. This indicates good compression. If released. test.
the needle fails to swing this far, there is
compression loss. Figure LO1-2.8 Vacuum-gauge readings and their
meanings.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 17

Note: Some V-type engines have a split intake manifold with no passage between the two sections. On
these engines, connect the vacuum gauge to each section and note the readings.

Another test using the vacuum pump is the cranking vacuum test. With the engine at
normal operating temperature, close the throttle valve and plug the PCV line. Disable
the ignition and crank the engine. An even cranking vacuum at normal cranking speed
indicates the engine is mechanically sound. Unevenness in the needle movement
indicates an air leak in one or more cylinders.

6. Exhaust Gas Analyzer – The exhaust
gas analyzer measures the amount of
various gases in the exhaust. There are
two main types:
a. Two-gas analyzer that measures HC
and CO.
b. Four-gas analyzer that measures HC,
CO, O2 and CO2

The purpose of making these

measurements is to help determine the

condition of the engine, ignition system,

fuel system and emission controls. On a

car with a catalytic converter, tail pipe

readings made with a two-gas analyzer

are often of little value. Normal action of

the catalyst reduces the HC and CO

nearly to zero.

Four-gas analyzers provide more

complete analysis of the tail pipe exhaust

gas. Carbon dioxide (CO2) and oxygen Figure LO1-2.9 Four-gas type of exhaust-gas
(O2) in the exhaust gas from the cylinder analyzer connected to tailpipe to test the exhaust
pass unchanged through the catalytic

converter. Measuring these gases at the gas. (ATW)

tail pipe gives a more complete picture of

the air-fuel mixture entering the cylinder

and the combustion process.

To use the exhaust-gas analyzer, block

off the air flow from the air-injection or

air-aspirator system. This prevents the

additional air from affecting the readings.

Insert the exhaust-gas pickup or probe

into the tail pipe of the car. The probe

draws out some of the exhaust gas and

carries it through the analyzer. Meters, a

display, or a printout show how much of Figure LO1-2.10 Two-gas type of exhaust-gas
each gas in the sample of exhaust gas. analyzer, which measures only hydrocarbons (HC)

and carbon monoxide (CO). (Chrysler

Corporation)

A different kind of tester measures NOx but it works in almost the same way. It draws
exhaust gas from the tail pipe and runs the gas through the analyzer. The finding is

reported in grams per mile. NO testers are usually only in testing laboratories. They are

not normally in automotive-service work.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 18

When testing exhaust emissions, follow the tester-manufacturer’s operating instructions.
Figure LO1-2.11 shows suggested testing specifications. Take the readings with the
engine idling at normal operating temperature. Repeat the tests with the engine running
at 1500 rpm and 2500 rpm.

Note: An exhaust gas analyzer can also be used to check for exhaust-gas leakage into
the cooling system. Figure LO1-2.11 shows the exhaust-gas analyzer being used to
locate fuel or fuel-vapor leaks.

7. Four-Gas Analysis – Combustion at Figure LO1-2.11 Suggested test specifications for
the stoichiometric ratio of 14.7:1 testing exhaust emissions.
provides maximum conversion
efficiency. This results in minimum tail
pipe emissions of HC and CO. Figure
12 shows the relationship among the
four gases measured by the four-gas
analyzer. Each gas and its readings
are described below.

HC Readings. The HC meter reports
the amount of hydrocarbon (unburned
gasoline) in the exhaust. It reports this
as parts per million (ppm). A reading of
200 means that every million parts of
exhaust gas has 200 parts of HC. The
exhaust gas of newer cars has less
than 100 ppm of HC. Older vehicles
are much higher emitters. Even in
good condition they may emit 400 ppm
or more. High HC could result from
trouble in the emission controls, or fuel
or ignition system. The air-fuel mixture
could be rich (or lean so there is
misfiring). The ignition system may be
out of time or misfiring. An engine with
worn rings and cylinders, burned
valves, or a blown head gasket emits
high levels of HC.

CO Readings. Carbon monoxide is a

by-product of combustion. The amount

of CO is measured as a percentage by

volume. One percent means that one Figure LO1-2.12 Relationship among the four gases
percent of the exhaust gas is CO. measured by the four-gas analyzer. (Sun

ElectricCorporation)

Some automotive engines produce less than 0.5 percent CO. A rich mixture or not

enough oxygen to burn the fuel produces excessive CO. Possible causes are misfiring,

a restricted air filter, and a leaking fuel injector or carburetor needle-end-seat.

CO2 Readings. Carbon dioxide is a product of combustion that is measured as a
percentage by volume. HC must burn to produce CO2. Any change in the air-fuel ratio

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 19

and the combustion process causes a change in CO2. Normally, CO2 is above eight
percent. The highest CO2 reading occurs at about the 14.7:1 stoichiometric air-fuel ratio.
Low CO2 readings indicate a rich mixture.

O2 Readings. These measure the percentage of oxygen remaining in the exhaust gas
after combustion has occurred. The air we breathe is about 21 percent oxygen. At idle,

the engine should produce less than three percent O2. If the engine is running richer
than 14.7:1, O2 is low. As the air-fuel mixture becomes leaner than 14.7:1, O2 increases.
When lean mixture occurs, O2 increases greatly.

8. Cylinder-Balance Test – The cylinder – Figure Lo1-2.13 All cylinders are contributing to
balance test determines if each cylinder the same amount of power if the tachometer
in a running engine produces the same
amount of power. Disabling a cylinder shows that all rpm drops are the same as each
should cause a change in engine speed. cylinder is disabled. (Sun Electric Corporation)
The change should be about the same
for all cylinders.
Connect a tachometer to the engine.
Then disable the cylinder. This is done
by shorting the spark plug or
disconnecting each fuel injector in a port-
injected engine. Note the tach reading.
Repeat the test on each cylinder. All
cylinders are contributing the same
amount of power if the rpm drops are the
same. Weaker cylinders show less of
rpm change. Shorting or disabling a dead
cylinder causes no change in rpm.

On some engines the ECM can run the cylinder-balance test automatically and store the
results. The technician signals the ECM to begin the test. The ECM then turns off the
fuel injector to each cylinder and measures engine rpm. This process repeats until
testing is completed.
Cylinder-balance testing can also be performed while watching the readings on a four-
gas analyzer. This may help diagnose the cause of a cylinder delivering low or no
power.

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ALT723302 March 4, 2006 20

9. Engine Analyzer – An engine analyzer
combines several testers, meters and
gauges into a single piece of portable
shop equipment. When connected to the
vehicle, the analyzer provides quick and
accurate testing and diagnosis of various
engine and vehicle systems. Most shop
engine analyzers include an
oscilloscope. It displays voltage patterns
of the ignition system and electronic fuel
injectors. Some computerized analyzers
include a second screen. This displays
information needed by the technician,
such as steps in a test procedure or the
test results. The analyzer may have a
printer to provide a written report.

Figure LO1-2.14 Engine analyzer that includes an
oscilloscope for displaying ignition voltages. (Sun

Electric Corporation)

Figure LO1-2.15. Computerized engine analyzer with two scope screens and a printer. (Sun Electric
Corporation)

10. Service-Bay Diagnostic Computer – Some new-car dealerships and other service-bay
diagnostic computer in Figure 15. This is a computerized engine-and-exhaust gas
analyzer with additional capabilities. Ideally, the system enables the vehicle to tell the
computer what is wrong. Then the system instructs the technician on how to make the
needed repairs.

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ALT723302 March 4, 2006 21

Many of these computers have a touch-sensitive screen. The technician first enters the
vehicle identification number then the technician answers a series of yes-no questions
about how the vehicle is equipped. The technician connects the computer to the
diagnostic connector on the vehicle. The computer then:
1. Automatically performs the test.
2. Interprets the results.
3. Shows the technician how to correct the faults.

In a dealership, the computer may automatically go online every night. This means the
computer connects itself through a phone line or satellite link to the vehicle-
manufacturer’s host computer. The host computer then sends or downloads the latest
information on:
• Factory product changes
• Diagnosis and repair techniques
• Vehicle specifications
• Service manual information
• Service bulletin summaries

During this same connection, the dealership computer sends or uploads information fed
into it during the day to the host computer. This provides overnight data exchange of the
latest service information between the dealer and the manufacturer. Similar systems are
available to independent shops. To provide the capabilities listed above, the computer
must store a wide range of service information. This information must be quickly
accessible and easily updated. Many computers store data on a compact disc (CD),
similar to the audio CD. When new information is needed, the technician replaces the
disc.

11. Dynamometer – the chassis dynamometer measures engine power and vehicle speed
under various operating conditions. The vehicle is driven onto two rollers so the drive
wheels can spin the rollers. The rollers drive a power absorber which is usually under
the floor. The vehicle remains stationary, but the engine and other components operate
the same as on a road test. Meters on a console report wheel speed and torque or
power.
The power absorber may be a heavy metal flywheel with an inertia weight, the same as
the weight of the vehicle. Or the power absorber may be a brake that places a variable
load on the rollers. The technician can connect an oscilloscope and a variety of other
testers to check the engine under operating conditions. When the vehicle is driven on
the dynamometer, the test instruments show engine performance while idling,
accelerating, cruising and decelerating. Shift points and other operating conditions of an
automatic transmission can also be checked.
Special dynamometers with two sets of rollers test all-wheel-drive vehicles. Diagnostic
dynamometers have sensitive motored rollers that may allow testing of wheel alignment,
suspension, steering and brakes.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 22

Engine Tune-up and Car Care

Definition of a tune-up

An engine tune-up restores drivability, power, performance and economy that have
been lost through wear, corrosion and deterioration of engine parts. These changes take
place gradually in many parts through time and mileage. This means the parts are affected
by normal aging of the vehicle (time) and by normal vehicle operation (mileage).
A tune-up means different things to different people. To some, it means a quick check of
the usual engine trouble spots. To others, it means using test instruments to do a complete
analysis of the engine and its systems. Then all worn parts are repaired or replaced and
everything is adjusted to specifications.

Tune-up Procedure:

An engine tune-up follows a procedure. Many technicians use a printed form supplied
by automotive or test-equipment manufacturers. By following the form and checking off the
items listed, one by one, the technician avoid overlooking any test in the procedure.

All tune-up forms are not the same. The procedure to follow depends on the vehicle and
the engine as well as the shop equipment available. If the shop has an oscilloscope or a
dynamometer, use it as part of the tune-up procedure.

Typical Tune-up Procedure

The steps in a typical tune-up procedure are given below. All steps do not apply to all
vehicles or to all engines.

1. Test and service the battery and starting motor. If the battery is low or the customer
complains that the battery keeps running down, check the charging system. If the
battery is defective. Install a new battery.

2. Inspect the drive belts. Replace any that are in poor condition. Replace both belts in
a two-V-belt set. Tighten the belts to the specified tension using a belt tension
gauge.

3. If the engine is cold, operate it for at least 20 minutes at 1500 rpm or until the engine
reaches normal operating temperature. Note any problems during warm-up.

4. Connect the engine analyzer or oscilloscope and perform an electrical diagnosis.
Check for any abnormal ignition-system condition and the cylinder in which it occurs.

5. Perform a comparison test. If necessary, perform a cylinder-leakage test and engine
vacuum tests. These provide additional information on engine condition. If
mechanical problems are found, tell the owner the engine cannot be tuned
satisfactorily until after it is repaired.

6. Remove the spark plugs and inspect the firing ends. Gap and install new spark
plugs. If reinstalling the old spark plugs, first clean, inspect, file, gap, and test them.

7. Inspect the ignition system. Look for the cause of any abnormal conditions seen with
the engine analyzer or oscilloscope. Check the condition of the distributor cap, rotor
and primary and secondary wiring. Replace any defective parts. On contact-point
ignition systems, clean and adjust (or replace) the contact points. Lubricate the
distributor cam. Check the centrifugal and vacuum advance devices. Adjust the
ignition timing.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 23

8. Recheck the ignition system with the oscilloscope. Any abnormal condition noted
earlier should now be gone.

9. Check the manifold heat-control valve. If used, it should move freely. Lubricate it
with heat-control-valve lubricant. Free or replace the valve, if necessary.

10. Test the fuel pump with a fuel-pump tester. Replace the fuel filter. Check the fuel-
tank cap, fuel lines and connections for leakage and damage.

11. Clean or replace the air-cleaner filter. If the engine has a thermostatic air cleaner,
check the operation of the vacuum motor.

12. Check the action of the throttle valves. Push the accelerator pedal to the floor to be
sure the throttle valves open fully. Check carburetor choke and fast-idle systems, if
used. Clean external linkages and check for binding.

13. Inspect all engine vacuum fittings, hoses and connections. Replace any brittle or
cracked hoses.

14. Clean the engine oil-filler cap, Inspect the conditions of its gasket or seal.
15. Check the cooling system. If necessary, fill it to the proper level with the specified

coolant. Check that the coolant contains the proper amount of antifreeze for
adequate freeze protection. Drain and install fresh coolant, if required by the vehicle
maintenance schedule. Inspect all hoses, connections, radiator, water pump and fan
clutch or electric fan. Pressure-check the cooling system and radiator cap. Squeeze
the hoses to check their condition. Replace any defective hoses or other parts.
16. Inspect the PCV system. Check and replace the PCV valve if necessary. Clean and
replace the PCV-system air filter if required. Inspect the PCV hoses and
connections. Replace any cracked or brittle hoses. Test the system for crankcase
vacuum.
17. If the engine has an air-injection pump, replace the pump inlet-air filter, if used.
Inspect the system hoses and connections. Replace any brittle or cracked hoses.
18. If the evaporative-control system uses an air filter in the charcoal canister, replace
the filter.
19. Check the transmission-controlled spark (TCS) system, if the vehicle is so equipped.
20. Inspect the EGR valve. Clean or replace it, as required. Inspect and clean the EGR
discharge port. Test system operation by applying vacuum to the valve with the
engine idling. The engine should run rough with vacuum applied then smooth out
with no vacuum.
21. Adjust the engine valves, if necessary. Some manufacturers recommend performing
this step first in the tune-up procedure.
22. Adjust the engine idle speed. Check the amount of HC and CO in the exhaust gas.
(Checking the HC and CO both before and after tune-up shows how much the tune-
up has reduced these pollutants.) If required, adjust the idle mixture (where
possible). Follow the procedure outlined on the VECI label in the engine
compartment.
23. If the engine has a turbocharger, check the wastegate operation. Follow the
procedure in the vehicle service manual.
24. Tighten the intake-manifold and exhaust-manifold bolts to the specified torque in the
proper sequence.
25. Check the maintenance sticker or the lubrication schedule to see if an oil and oil-
filter change are due. Also note the schedule for chassis lubrication. Recommend
the services due to the vehicle owner.
26. While the car is on the lift, check the exhaust system for leaks. These could admit
deadly carbon monoxide (CO) into the passenger compartment. Also look for loose
bolts, rust spots and heat-shield and other under-car damage.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 24

27. Road-test the car on a dynamometer or on the road. Check for driveability, power
and idling. Any abnormal condition now may require additional checking and service
to other parts or systems. Always note any uncorrected abnormal condition on the
repair order before returning the car to the customer. If possible, explain the notes
on the repair order to the customer. Conditions that affect emissions, fuel economy,
reliability and safety may need immediate attention.

Steps in Vehicle Maintenance

1. Before road-testing the car, check the tires for specified inflation pressure and for
abnormal wear. Abnormal wear would mean suspension trouble and the need for
wheel alignment.

2. Check for proper operation of the instruments-panel warning lights, gauges, and
information displays.

3. Check the brakes for even and adequate braking.
4. Check the steering system for ease and smoothness of operation. Check for

excessive play in the steering system.
5. Check the suspension system for looseness, excessive play and wear. Check the

front-suspension ball joints for excessive wear. Check for loose wheel bearings at
the non-driving wheels. Adjust the wheel bearings if necessary.
6. Check the CV joints for noise and smooth operation. If a CV-joint boot is torn, check
for grit in the grease and for joint wear.
7. Check the operation of the clutch and manual transmission or transaxle. Note the
shift timing and shift quality in a vehicle with an automatic transmission or transaxle.
8. Note any unusual noise, vibrations or hardness heard or felt during the road test.
9. Check the headlights and horns to make sure they work. Check all other lights.
Replace burned-out bulbs. Check headlights aim, if necessary.

The preceding list of steps for tune-up and car care covers conditions that frequently
need service or cause trouble. When performed as a complete procedure, These steps
will locate many abnormal conditions that affect drivability and performance. Correcting
these conditions will improve vehicle performance and reliability.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 25

SELF-CHECK LO1-1

Multiple-Choice Test

Select the correct answer to each question.

1. When connected to the engine, the tachometer measures
a. engine torque
b. engine rpm
c. engine compression
d. engine vacuum

2. After the engine is at normal operating temperature, the first step in using the
compression tester is to:
a. disconnect the battery
b. adjust engine idle
c. remove the spark plugs
d. shift the transmission into low gear

3. The purpose of squirting a small amount of oil through the spark-plug hole while
compression-testing the cylinder is to
a. lubricate the piston rings
b. see if the compression pressure increases
c. measure manifold vacuum
d. make it easier to install the spark plugs

4. If squirting engine oil through the spark-plug hole does not increase compression
pressure, all the following could be the cause except
a. leakage past the valves
b. a broken valve spring
c. worn camshaft lobe
d. worn oil-control rings

5. A compression test on an in-line six-cylinder engine shows that cylinders 3 and 4
have readings of 10 psi [69 kPa]. The other cylinders all read between 130 and 135
psi [897 and 892 kPa]. Technician A says this is probably due to a blown head
gasket. Technician B says the cause could be improper valve timing. Who is right
a. A only
b. B only
c. both A and B
d. neither A nor B

6. The cylinder leakage tester applies air pressure to the cylinder with the piston
a. at TDC with both valves closed
b. at BDC with both valves closed
c. starting the compression stroke
d. at TDC with both valves open

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 26

7. A vacuum-gauge needle that swings around to 23 to 25 inches [584 to 635 mm] of
mercury after the throttle is quickly opened and released indicates
a. stuck valves
b. low compression
c. good compression
d. leaky valves

8. A steady but low vacuum reading with no engine idling indicates that the engine
a. is losing power
b. has a stuck valve
c. exhaust system is restricted
d. ignition timing is advanced

9. Technician A says to use tail pipe measurements of HC and CO to check the
operation of the catalytic converter. Technician B says tail pipe measurements of O2
and CO2 indicate the air-fuel ratio of the mixture entering the cylinder. Who is right?
a. A only
b. B only
c. both A and B
d. neither A nor B

10. A service-bay diagnostic computer may do the following except
a. automatically perform tests
b. interpret the results
c. show how to correct faults
d. grade the technician’s work

Review Questions

1. What can be learned by making a cylinder-balance test?

2. Where does a service-bay diagnostic computer get information and how is this
information updated?

3. What is the use of a chassis dynamometer and what can its use tell the technician?

4. What is a tune-up and how is it performed?

5. What record should the technician make of any abnormal condition found during the
road test?

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 27

ANSWER KEY LO1-1

Multiple-Choice Test

1. b

2. c

3. b

4. d

5. a

6. a

7. c

8. c

9. a

10. d

Review Questions

1. A test to check if each cylinder in a running engine produces the same amount of
power.

2. Information is gathered via a phone or satellite link from the vehicle manufacturer’s
host computer and downloads the latest information on vehicle service.

3. The chassis dynamometer measures engine power and vehicle speed under
various operating conditions and tells the technician the wheel speed and torque.

4. Tune-up restores drivability, power, performance and economy that have been lost
through wear, corrosion and deterioration of engine parts and performed by
testing, adjusting and replacing parts or components of the engine following a
checklist or form supplied by automotive or test-equipment manufacturers.

5. Driveability, power and idling. Note any uncorrected abnormal condition on the
repair order of the vehicle.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 28

QUALIFICATION : Automotive Servicing NC I

UNIT OF COMPETENCY : Perform Gas Engine Tune Up

MODULE TITLE : Performing Gas Engine Tune Up

LEARNING OUTCOME 2 : Check/adjust tappet valve clearance

ASSESSMENT CRITERIA:
1. Valve tappet clearance is set.
2. Checking and adjustment is performed.

RESOURCES:

1. Auto Mechanics, Theory and Service
by: de Kryger, Kobacik. Bono

2. Corolla, Service and Repair Manual
by: Gregory’s Scientific Publication

3. Lancer, Service and Repair Manual
by: Gregory’s Scientific Publication

4. Toyota Training Manual
by: Toyota

5. VHS/CD

6. Corolla, Owners Manual
by: Toyota

7. Communication Module

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 29

LEARNING EXPERIENCES

Learning Outcome # 2: Check/adjust valve tappet clearance

Learning Activities Special Instructions

1. Perform checking/adjustment of valve • Follow the procedures in Operation
tappet on a gasoline engine with the Sheet LO2-1 “Check/Adjust Valve
presence of your instructor. Tappet Clearance”.

2. Check your knowledge and skill in this • Complete the assessment tasks.
learning outcome.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

ALT723302 March 4, 2006 30

LO2 - CHECK/ADJUST VALVE TAPPET CLEARANCE

LEARNING OUTCOME:

At the end of this learning activity you should be able to check and adjust valve
tappet clearance of a gasoline engine.

TOOLS, EQUIPMENT AND MATERIALS:

• Running condition engine
• Flat screwdriver
• Service manual
• Set of wrenches
• Spark plug wrench
• Feeler gauge

LEARNING ACTIVITIES:

Activity # 1: Adjusting engine valve tappet clearance

Do you know the correct valve tappet clearance?

a. Read Operation Sheet LO2-1, and then answer these questions.

• What would result if the valve tappet clearance is insufficient?
• What would happen when the clearance is too much?

b. Perform checking/adjustment of valve tappet on a gasoline engine with the
presence of your instructor.

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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OPERATION SHEET LO2-1: ADJUSTING VALVE TAPPET CLEARANCE

The valve-train clearance on engines with solid or mechanical valve lifters (tappets) must
be adjusted after any cylinder-head or valve service. The vehicle maintenance schedule
may also require a valve adjustment periodically. This is the same as adjusting valve
clearance or making a tappet or lash adjustment. “Lash” means freeplay or clearance.
Engines with hydraulic valve lifters and lash adjusters normally require no adjustment of
valve-train clearance. The clearance is taken up hydraulically. The hydraulic lifter or lash
adjuster also takes care of any small changes in the valve-train length.
In any valve train, refinishing the valves and seats reduces valve-train clearance. Too much
clearance results from worn valve-train parts. Because exhaust valves run hotter and
expand more, exhaust-valve clearance usually is greater than intake-valve clearance. Too
much valve clearance causes noise and poor engine performance. Too little valve
clearance causes valve and seat burning.

Adjusting Valve Clearance in Engines with Solid-Lifter Overhead Valve (OHV)

The engine should be off and at normal
operating temperature.

1. Disable the ignition and remove the valve
cover.

2. Bump the crankshaft with the starting motor
until the heel or base circle of the cam is
under the valve lifter.

Figure LO2-1.1 Cam Figure LO2-1.2 Operation of the valve train in an
on the camshaft. Note overhead-valve engine.
location of the toe and

heel.

3. Measure the clearance between the valve
stem and rocker arm with a thickness gauge
(feeler gauge).

4. Turn the adjusting screw until the clearance
is within the manufacturer’s specifications.

5. Tighten the locknut and recheck the
clearance.

Figure LO2-1.3 Adjusting valve clearance on an
OHV engine that has solid lifters and shaft-
mounted rocker arm. (Ford Motor Company)

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Adjusting Hydraulic Valve Lifters on OHV Engines

Adjustment of the hydraulic-lifter initial setting may be needed after resurfacing the cylinder
head or refinishing the valves and seats. This adjustment should properly position the lifter
plunger in the center of its travel. Sometimes additional clearance is needed and no
adjustment method is provided by the engine manufacturer. Then up to 0.020 inch (0.5
mm) may be ground off of the tip end of the valve stem. An excessively high valve stem will
bottom the plunger in the lifter.

1. Ford OHV Engines.

a. Turn the crankshaft until the lifter is
on the base circle of the cam.

b. Use a tappet collapser to force the oil
out of the lifter.

Figure LO2-1.4 Using a thickness gauge to check the
clearance between an engine rocker arm and valve

stem. (Ford Motor Company)

c. This bottoms the plunger in the lifter.

d. Check valve clearance with a
thickness gauge.

e. Install a longer pushrod is the
clearance is excessive. Pushrods are
available in various lengths.

f. If the clearance is too small, use a
shorter pushrod.

Figure LO2-1.5 Hydraulic valve lifter with valve
closed and open. (Chrysler corporation)

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2. Chevrolet OHV Engines

a. With the valve lifter on the base circle
of the cam, back off the stud nut until
the pushrod is loose.

b. Slowly turn the adjusting nut down
while rotating the pushrod with your
fingers.

c. When the pushrod tightens and will
not rotate easily, turn down the
adjusting nut one additional full turn.

d. This positions the valve lifter plunger Figure LO2-1.6 Adjusting the valve rocker arm-stud
in the center of its travel. nut to properly position the plunger in the hydraulic
valve lifter. (Chevrolet Division of General Motors
Adjusting Valves on OHC Engines
Corporation)

Overhead-camshaft (OHC) engine use a variety of valve trains to operate the valves (Fig.
14-1). OHC engines with hydraulic tappets (Fig. 14-8) or lash adjusters normally do not
require valve adjustments. Various adjusting methods are used with mechanical tappets.
On an OHC engine, always check valve-train clearance every time the cylinder head is
resurfaced. Cylinder-head resurfacing changes the center-to-center distance between the
crankshaft and the camshaft. This then affects valve timing.

1. Solid Bucket Tappets

a. Rotate the crankshaft until the
tappet is loose.

b. Measure the clearance between
the adjusting shim and the base
circle of the cam with a thickness
gauge.

c. Change the thickness of the shim
to adjust the clearance.

d. To remove the shim, a special
spring depressor may be needed
to slightly compress the spring.

e. Then remove the shim with special
pliers.

Figure LO2-1.7 Valve train with bucket tappets showing
location of adjusting shims inside the bucket tappets.
(Chevrolet Division of General Motors Corporation)

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2. Adjustable Shaft-Mounted Rocker Arms
A single overhead camshaft (SOHC) uses adjustable rocker arms mounted on shafts to
operate the valves.

a. Rotate the crankshaft until the Figure LO2-1.8 OHC-engine valve train using adjustable
rocker arm is on the base circle of rocker arms on shafts to operate the valves. (American
the cam.
Honda Motor Company, Inc.)
b. Measure the clearance between
the rocker-arm adjusting screw and
the valve stem.

c. If adjustment is necessary, hold the
adjusting screw with a screwdriver
(Fig 39-12B).

d. Loosen the locknut and turn the
adjusting screw to get the specified
clearance.

e. Then tighten the locknut and
recheck the clearance.

3. Adjustable Stud-Mounted Rocker Arms

a. Turn the crankshaft until the lifter is
on the base circle of the cam.

b. Measure the clearance between
the rocker-arm and the valve stem

c. Adjust the clearance by turning the
stud nut.

Valve train for an OHC engine using a rocker arm. The
valve-train clearance is adjustable by turning the nut on

the rocker-arm stud.

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4. Adjustable Stud and Floating Rocker Arms

a. Rotate the crankshaft until the
base circle of the cam is over the
center of the rocker arm.

b. Measure the clearance between
the two with a thickness gauge (Fig
39-13.

c. Adjust the clearance by loosening
the locknut and turning the
adjusting screw.

d. Turning the screw increases
clearance.

e. After making the adjustments,
tighten the locknut.

f. Then recheck the clearance.

Figure LO2-1.10 Checking valve clearance on an OHC
engine using rocker arms. (Ford Motor Company)

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ASSESSMENT TASKS:

These assessment tasks should be completed when you are confident that you can
adjust valve tappet clearance of a gasoline engine. Assessment needs to conform to the
rules of evidence. Therefore:
• You will need to participate and complete the learning activities
• You will demonstrate tasks to the required standard

• You will answer oral and written questions
• You will complete the assessment tool

OBSERVATION CHECKLIST:

Self Component Trainer’s check
check
Competent Not yet
competent

High tension coil wire is disconnected and
properly grounded.

Valve tappet cover is removed properly

Spark plugs are removed properly.

Engine is adjusted to TDC, timing marks

Valve tappet clearance is set.

Checking and adjustment is performed.

Tools are properly used and stored.

Work area is cleaned.

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QUALIFICATION : Automotive Servicing NC I

UNIT OF COMPETENCY : Perform Gas Engine Tune Up

MODULE TITLE : Performing Gas Engine Tune Up

LEARNING OUTCOME 3 : Test spark plug

ASSESSMENT CRITERIA:
1. Spark plug clearance is adjusted.
2. Spark plug is tested.
3. Spark plug test result analyzed and appropriate recommendations are prescribed

RESOURCES:

1. Auto Mechanics, Theory and Service
by: de Kryger, Kobacik. Bono

2. Corolla, Service and Repair Manual
by: Gregory’s Scientific Publication

3. Lancer, Service and Repair Manual
by: Gregory’s Scientific Publication

4. Toyota Training Manual
by: Toyota

6. VHS/CD

6. Corolla, Owners Manual
by: Toyota

7. Communication Module

Code No. Performing Gas Engine Tune Up Date: Developed Date: Revised Page #

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LEARNING EXPERIENCES

Learning Outcome # 3: Test spark plug Special Instructions
Learning Activities

1. Define the purpose and functions of • Read Information Sheet LO3-1 “Spark
the spark plug. Identify the conditions Plug Overview”
that affect spark plug operation.
• Read Information Sheet LO3-2
2. Identify defects of used spark plugs. “Reading and Understanding Spark
Compare with actual spark plugs in Plugs”
your shop.

3. Perform gapping of spark plugs. • Follow the procedures in Operation
Sheet LO3-1 “Gapping the Spark
Plug”.

4. Check your knowledge and skill in this • Complete the assessment tasks.
learning outcome.

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LO3 - TEST SPARK PLUG

LEARNING OUTCOME:

At the end of this learning activity you should be able to adjust spark plug clearance
and test it on a gasoline engine.

TOOLS, EQUIPMENT AND MATERIALS:

• Running condition engine
• Vehicle service/repair manual
• Spark plug socket wrench (magnetic) and handle
• Wire gauge, ramp gauge or feeler gauge
• Ignition spark tester
• Spark plug tester

LEARNING ACTIVITIES:

Activity # 1: Inspect and test spark plug

a. Read Information Sheets LO3-1 and LO3-2 and perform the following:

• Inspect spark plugs removed from a vehicle?
• Test the serviceability of spark plug using a spark plug tester?

b. Perform adjustment/testing of spark plug on a gasoline engine with the
presence of your instructor.

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INFORMATION SHEET LO3-1: Spark Plugs Overview

Spark plugs are one of the most misunderstood components of an engine. Numerous
questions have surfaced over the years, leaving many people confused.
This guide was designed to assist the technician, hobbyist, or race mechanic in
understanding, using, and troubleshooting spark plugs. The information contained in this
guide applies to all types of internal combustion engines: two stroke engines, rotary
engines, high performance/racing engines and street vehicles.
Spark plugs are the "window" into your
engine (your only eyewitness to the
combustion chamber), and can be used
as a valuable diagnostic tool. Like a
patient's thermometer, the spark plug
displays symptoms and conditions of
the engine's performance. The
experienced tuner can analyze these
symptoms to track down the root cause
of many problems, or to determine
air/fuel ratios.

SPARK PLUG BASICS:

The spark plug has two primary functions:
• To ignite the air/fuel mixture

• To remove heat from the combustion chamber

Spark plugs transmit electrical energy that turns fuel into working energy. A sufficient
amount of voltage must be supplied by the ignition system to cause it to spark across the
spark plug's gap. This is called "Electrical Performance."

The temperature of the spark plug's firing end must be kept low enough to prevent pre-
ignition, but high enough to prevent fouling. This is called "Thermal Performance", and is
determined by the heat range selected.

It is important to remember that spark plugs do not create heat, they can only remove
heat. The spark plug works as a heat exchanger by pulling unwanted thermal energy away
from the combustion chamber, and transferring the heat to the engine's cooling system.
The heat range is defined as a plug's ability to dissipate heat.

The rate of heat transfer is determined by:

• The insulator nose length

• Gas volume around the insulator nose

• The materials/construction of the center electrode and porcelain insulator

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A spark plug's heat range has no relationship to the actual voltage transferred though the
spark plug. Rather, the heat range is a measure of the spark plug's ability to remove heat
from the combustion chamber. The heat range measurement is determined by several
factors; the length of the ceramic center insulator nose and its' ability to absorb and transfer
combustion heat, the material composition of the insulator and center electrode material.

Heat rating and heat flow path of NGK Spark Plugs

The insulator nose length is the distance from the firing tip of the insulator to the point
where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark
plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark
plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must
remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area
surrounding the center electrode will not be hot enough to burn off carbon and combustion
chamber deposits. These accumulated deposits can result in spark plug fouling leading to
misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may
cause the ceramic around the center electrode to blister and the electrodes to melt. This
may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug
types, the difference from one heat range to the next is the ability to remove approximately
70°C to 100°C from the combustion chamber. A projected style spark plug firing tip
temperature is increased by 10°C to 20°C.

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Tip Temperature and Firing End Appearance

The firing end appearance also depends on the spark plug tip temperature. There are three
basic diagnostic criteria for spark plugs: good, fouled and overheated. The borderline
between the fouling and optimum operating regions (500ºC) is called the spark plug self-
cleaning temperature. The temperature at this point is where the accumulated carbon and
combustion deposits are burned off.

Bearing in mind that the insulator nose length is a determining factor in the heat range of a
spark plug, the longer the insulator nose, the less heat is absorbed, and the further the heat
must travel into the cylinder head water journals. This means the plug has a higher internal
temperature, and is said to be a hot plug. A hot spark plug maintains a higher internal
operating temperature to burn off oil and carbon deposits, and has no relationship to spark
quality or intensity.

Conversely, a cold spark plug has a shorter insulator nose and absorbs more combustion
chamber heat. This heat travels a shorter distance, and allows the plug to operate at a
lower internal temperature. A colder heat range is necessary when the engine is modified
for performance, subjected to heavy loads, or is run at high rpms for a significant period of
time. The colder type removes heat more quickly, and will reduce the chance of pre-
ignition/detonation and melting or damage to the firing end. (Engine temperature can affect
the spark plug's operating temperature, but not the spark plugs heat range).

Below is a list of some of the possible external influences on a spark plug's operating
temperatures. The following symptoms or conditions may have an effect on the actual
temperature of the spark plug. The spark plug cannot create these conditions, but it must
be able to cope with the levels of heat...if not, the performance will suffer and engine
damage can occur.

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Air/Fuel Mixtures seriously affect engine performance and spark plug operating
temperatures.

• Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor
driveability

• Lean air/fuel mixtures cause plug tip and cylinder temperature to increase, resulting
in pre-ignition, detonation, and possibly serious spark plug and engine damage

• It is important to read spark plugs many times during the tuning process to achieve
the optimum air/ fuel mixture

Higher Compression Ratios/Forced Induction will elevate spark plug tip and in-cylinder
temperatures

• Compression can be increased by performing any one of the following modifications:

a) reducing combustion chamber volume (i.e.: domed pistons, smaller chamber
heads, milling heads, etc.)

b) adding forced induction (Nitrous, Turbocharging or Supercharging)

c) camshaft change

• As compression increases, a colder heat range plug, higher fuel octane, and careful
attention to ignition timing and air/fuel ratios are necessary. Failure to select a colder
spark plug can lead to spark plug/engine damage

Advancing Ignition Timing

• Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-
100° C

Engine Speed and Load

• Increases in firing-end temperature are proportional to engine speed and load. When
traveling at a consistent high rate of speed, or carrying/pushing very heavy loads, a
colder heat range spark plug should be installed

Ambient Air Temperature

• As air temperature falls, air density/air volume becomes greater, resulting in leaner
air/fuel mixtures.

• This creates higher cylinder pressures/temperatures and causes an increase in the
spark plug's tip temperature. So, fuel delivery should be increased.

• As temperature increases, air density decreases, as does intake volume, and fuel
delivery should be decreased

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Humidity

• As humidity increases, air intake volume decreases

• Result is lower combustion pressures and temperatures, causing a decrease in the
spark plug's temperature and a reduction in available power.

• Air/fuel mixture should be leaner, depending upon ambient temperature.

Barometric Pressure/Altitude

• Also affects the spark plug's tip temperature

• The higher the altitude, the lower cylinder pressure becomes. As the cylinder
temperature decreases, so does the plug tip temperature

• Many mechanics attempt to "chase" tuning by changing spark plug heat ranges

• The real answer is to adjust jetting or air/fuel mixtures in an effort to put more air
back into the engine

Types of Abnormal Combustion

Pre-ignition

• Defined as: ignition of the air/fuel mixture before the pre-set ignition timing mark

• Caused by hot spots in the combustion chamber...can be caused
(or amplified) by over advanced timing, too hot a spark plug, low octane fuel, lean
air/fuel mixture, too high compression, or insufficient engine cooling

• A change to a higher octane fuel, a colder plug, richer fuel mixture,
or lower compression may be in order

• You may also need to retard ignition timing, and check vehicle's cooling system

• Pre-ignition usually leads to detonation; pre-ignition an detonation are two separate
events

Detonation

• The spark plug's worst enemy! (Besides fouling)

• Can break insulators or break off ground electrodes

• Pre-ignition most often leads to detonation

• Plug tip temperatures can spike to over 3000°F during the combustion process (in a
racing engine)

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• Most frequently caused by hot spots in the combustion chamber.
Hot spots will allow the air/fuel mixture to pre-ignite. As the piston is being forced
upward by mechanical action of the connecting rod, the pre-ignited explosion will try
to force the piston downward. If the piston can't go up (because of the force of the
premature explosion) and it can't go down (because of the upward motion of the
connecting rod), the piston will rattle from side to side. The resulting shock wave
causes an audible pinging sound. This is detonation.

• Most of the damage than an engine sustains when "detonating" is from excessive
heat

• The spark plug is damaged by both the elevated temperatures and the
accompanying shock wave, or concussion

Misfires

• A spark plug is said to have misfired when enough voltage has not been delivered to
light off all fuel present in the combustion chamber at the proper moment of the
power stroke (a few degrees before top dead center)

• A spark plug can deliver a weak spark (or no spark at all) for a variety of
reasons...defective coil, too much compression with incorrect
plug gap, dry fouled or wet fouled spark plugs, insufficient ignition timing, etc.

• Slight misfires can cause a loss of performance for obvious reasons (if fuel is not lit,
no energy is being created)

• Severe misfires will cause poor fuel economy, poor drivability, and can lead to
engine damage

Fouling

• Will occur when spark plug tip temperature is insufficient to burn off carbon, fuel, oil
or other deposits

• Will cause spark to leach to metal shell...no spark across plug gap will cause a
misfire

• Wet-fouled spark plugs must be changed...spark plugs will not fire

• Dry-fouled spark plugs can sometimes be cleaned by bringing engine up to
operating temperature

• Before changing fouled spark plugs, be sure to eliminate root cause of fouling

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