Performing Diesel Engine Tuneup

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Notes Format of Learner’s Guide

Course: Automotive Servicing NC II
Unit of competency: Perform Diesel Engine Tune UP

Module: At the end of the session, learners should be able to:
Learning outcomes:

1. Prepare tools and equipment
2. Set and install injection pump to engine
3. Inspect injection timing
4. Bleed injection system components
5. Conduct compression test

Duration: 40 Hours
Situating Learning:
You are a new technician in Hino Inc. (A company that specializes a
diesel engine) . Being a technician, your supervisor gives you some
errors of injection fuel system. He advice you to perform engine tune
up which is part of the engine trouble shooting. In order for you to
conduct engine tune up, you need to determine the following:

1. Fuel pump is functioning properly
2. Injection timing is set up properly
3. Corresponding recommendation/prescription is given based on

the test result
4. Manufacturer specification

Your senior supervisor expects that you can perform the job
competently.

Assessment Criteria: A technician will be given an incentive pay, if he can finish his work
before the prescribe time.
The foreman will declare the work finished, if the work function
correctly.
1. Setting/installation of injection pump is performed in accordance

with manufacturer’s manual specifications.
2. Timing marks and torque of injection pump moving parts is

checked before installation.
3. Injection pump timing device is used without error.
4. Injection pump timing result is interpreted correctly.
5. Bleeder screw and prime pump is determined and used properly.
6. Procedures on bleeding injection system are followed guided by

the service manual.
7. Engine requirements in compression testing is set and prepared.
8. Read and interpreted specific compression test result.

Pedagogical Training in Instructional Design & Delivery for TVET Page 1
© 2010, Institute of Technical Education, Singapore

DLM 03 Developing print-based Learner’s Guide including all related documents
Notes Format of Learner’s Guide

Learning chunk Performance Learning Activities Learning documents
Criteria (Brief description of (Documents
strategies, sequence
of lesson, evaluation) referenced by each
learning activity)

Perform Diesel Engine
Tune Up

1. Prepare tools and Appropriate tools and 1.1 Identify tools and • Read information
equipment equipment prepared equipment according to Sheet 1.1.1
and selected. their uses. identifying the tools
2. Set and install injection
pump to engine and equipment

according to their

uses

• Worksheet 1.1.2

1. Timing marks torque 2.1 Explain the operating • Read information

and injection pump principles of diesel engine. sheet 2.1.1

moving parts motion explaining operating

is re-checked before principles of diesel

installation. engine

2. Injection timing • Worksheet 2.1.2

setting is rechecked 2.2 Explain the operating • Read information

following principles of diesel engine sheet 2.2.1
explaining operating
instructional manual. preheating system.

3 Mounting bolts are principles of diesel

tightened following engine preheating

torque sequence, system

pattern and • Worksheet 2.2.2

specification in the 2.3 Identify the diesel fuel • Read information
manual. system components and its sheet 2.3.1
4. Injection pump functions. identifying the diesel
requirement in fuel system
installing injection 2.4 Identify the parts and • components and its
pump per manual functions of injection pump. functions
instruction is set-up. • Worksheet 2.3.2
5. No error in Read information
detecting/reading sheet 2.4.1
injection timing identifying the parts
setting. and functions of

injection pump

2.5 Identify the parts, types • Worksheet 2.4.2
and functions of diesel fuel
injector. • Read information
sheet 2.5.1

identifying the parts,

types and functions

of diesel fuel injector

2.6 Perform check injector • Worksheet 2.5.2
nozzle. • Read job sheet

2.6.1performing

checking injector

nozzle

2.7 Identify the correct • Read information
timing of fuel injection sheet 2.7.1
marks, location and their identifying the
purpose. correct timing of fuel

injection marks,

Pedagogical Training in Instructional Design & Delivery for TVET Page 2
© 2010, Institute of Technical Education, Singapore

DLM 03 Developing print-based Learner’s Guide including all related documents
Notes Format of Learner’s Guide

Learning chunk Performance Learning Activities Learning documents
Criteria (Brief description of (Documents
3. Inspect injection timing strategies, sequence
of lesson, evaluation) referenced by each
4. Bleed injection system learning activity)
components 2.8 Perform the procedures
in setting and installing of location and their
5. Conduct compression injection pump to engine. purpose
testing • Worksheet 2.7.2
1. Injection re- checking 3.1 Identify the parts and • Read jod sheet
timing device is used functions of timing device. 2.8.1 performing in
without error. setting and installing
3.2 Perform procedures in of injection pump to
2. Result is interpreted inspecting injection timing. engine.
without error. • Read information
3.1.1 identifying
3. Timing advance parts and function of
operation is checked. timing device
• Worksheet 3.1.2
1. Fuel level, line 4.1 Perform procedures in • Read job sheet 3.2.1
leakage and fuel bleeding of injection performing in
strainer/filter are system components. inspecting injection
timing
checked. • Read job sheet
4.1.1 Performing in
2. Air lock free fuel bleeding of injection
system components
system is determined
• Perform job sheet
without error. 5.1.1 procedures in
conducting
3. Bleed screw and compression testing
of diesel engine
primer pump is identified
• Worksheet 5.1.2
without error.

1. Engine requirements 5.1 Perform procedures in
in compression testing conducting compression
is set up. testing of diesel engine.

2. Specific compression

test result is read and

interpreted.

3. Corresponding

recommendation/

prescription is given

based on the test

result.

Pedagogical Training in Instructional Design & Delivery for TVET Page 3
© 2010, Institute of Technical Education, Singapore

Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

Learning Outcome: 1. Identify tools and equipments and their uses for a job
Learning Activity: 1.1 Identify tools and equipments and their uses for a job.

GENERAL CLASSIFICATION OF TOOLS AND EQUIPMENTS

1) HAND TOOLS – Are tools that the source of power is by hand only.
2) POWER TOOLS – Are tools powered by: electric, Air or Pneumatic and Hydraulic.
3) MEASURING TOOLS – Are tools used to measure of an object such; length, deep, diameters,

width and height.

1.) TYPES OF HAND TOOLS:

a.)TURNING TOOLS
Examples: Wrenches used to tighten or loosen the bolts and nuts

Open End Wrench - used to tighten or loosen
bolts and nuts

Combination Wrench – used to tighten or
loosen bolts and nuts

Adjustable Wrench – used to tighten or
loosen bolts and nuts

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
ALT723301 Aug 15, 2003
Sept. 20, 2010 1

Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

Socket Wrench – used to tighten or loosen
bolts and nuts

Pipe Wrench – used to hold, tighten or loosen
round objects such pipe

Allen Wrench – used to tighten or loosen
Allen head bolt

Box end wrench – used to tighten or loosen
the bolts and nuts

Ratcheting Wrench – used to tighten or
loosen bolts and nuts

Sparkplug Wrench – used to tighten or
loosen spark plugs

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

Torque Wrench (Point Type) – used to
measure the tightness of bolts and nuts

Torque Wrench (Dial Type) – used to
measure the tightness of bolts and nuts

Torque Wrench (Click Type) – used to
measure the tightness of bolts and nuts

b.) Driving Tools
Examples: Screwdrivers used to turn the screws for tightening or loosening either flat, star or
torx the shape of the head.

Philips/Star screwdriver

Flat screwdriver

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job
Offset screwdriver

Insulated screwdriver

Precision screwdriver
Torx set screwdriver

Bits Screwdriver

Nut drivers

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job
c.) Gripping Tools

Examples: Pliers used to hold an object, cut and stripes wires, install and
remove snap ring.

Locking pliers

Diagonal pliers

Slip joint pliers

Long nose pliers
Channel lock Pliers

Wire Stripper

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job
Internal snap ring pliers

External snap ring pliers

d.) Striking Tools
Examples: Hammers used for striking an object
Ball peen hammer

Rubber mallet Hammer

Dead blow hammer

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

Mallet hammer

e.) Cutting tools – Hacksaw used to cut metals.
Files used to smooth such metal object
Punchers used to align, guide or make an initial hole when drilling

Hack saw

Files

Punchers

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

2.) TYPES OF POWER TOOLS

a.) Electric powered

Soldering Iron is used to solder wires,
terminals on electrical components

Air compressor as source of air needed in
the shop such; cleaning of engine parts

Trouble light used to illuminate or give lights
on workplace like under the car or under the
hood

b.) Hydraulic powered

Car lifter a machine used to lift the whole car
in order for the technician to work under

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

Hydraulic Press a machine used to press in
or press out such bearing or liner

Crocodile jack a tool used to lift a car even
one side or one tire

Portable crane used to lift engine

c.) Pneumatic/air powered

Parts cleaner a tool used to clean such
engine parts using chemical inside the
container and blown by air from air
compressor

Air gun a tool used to clean objects by using
air from air compressor

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

Impact wrench used to loosen or tighten the
bolts and nuts with the socket attached on it
and powered by air

Air chisel a tool used to cut an object

3. MEASURING TOOLS

L square used for linear measurement the
squareness of such lay out

Steel rule used for linear measurement
within the range

Straight edge used to measure the warpage
of cylinder head by lying on top and insert a
feeler gauge on it

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

Feeler Gauge used to measure the
clearances thickness

Vernier caliper a precision measuring tool
used to measure the length, width, height,
diameter, and depth of an object within the
range

Micrometer a precession measuring tool
used to measure the length, width, height,
and diameter of an object within the range

Compression gauge a measuring tool used
to measure the compression inside the
cylinder of an engine

Steel Tape used to measure linear within the
range

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 1.1.1: Identify Tools and Equipments and their uses required the job

Nozzle Tester is used test the opening
pressure and spray pattern of every nozzle

Calibrating Machine is used to measure the
amount of fuel delivered for every cylinder as
per engine specification

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Worksheet 1.1.2 Identify tools and equipments
Learning outcomes:

1 Prepare tools and equipments according to their uses

Learning Activity:

1.2 Identify tools and equipments according to each uses

I. Give 10 examples of wrenches
1. ____________________
2. ____________________
3. ____________________
4. ____________________
5. ____________________
6. ____________________
7. ____________________
8. ____________________
9. ____________________
10. ____________________

II. Give 5 examples of screwdrivers
1. ____________________
2. ____________________
3. ____________________
4. ____________________
5. ____________________

III. Give 10 examples of measuring tools
1.______________________
2.______________________
3.______________________
4.______________________
5.______________________
6.______________________
7.______________________
8.______________________
9.______________________
10._____________________

Code No. Perform Diesel Engine Tune up Date: Developed Date: Revised Page #
ALT723307
Nov. 28, 2003 Sept. 20, 2010 1

Worksheet 1.1.2 Identify tools and equipments

Answers Key:

I. Kinds if wrenches
1. Open end wrench
2. Box end wrench
3. Combination Wrench
4. Socket Wrench
5. Allen wrench
6. Pipe wrench
7. Adjustable Wrench
8. Impact Wrench
9. Torque Wrench
10. Ratcheting Wrench

II. Kinds if screwdrivers
1 .Flat screwdriver
2. Philips screwdriver
3. Torx screwdriver
4. Nut driver
5. Offset screwdriver
6. Precision screwdriver
7. Insulated screwdriver

III.Kinds of Measuring Tools
1. Steel rule
2. Square rule
3. Steel tape
4. Vernier caliper
5. Micrometer
6. Compression gauge
7. Nozzle tester
8. Calibrating machine
9. Feeler gauge

Code No. Perform Diesel Engine Tune up Date: Developed Date: Revised Page #
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Nov. 28, 2003 Sept. 20, 2010 2

Information Sheet 2.1.1: Explain the operating principles of diesel engine
Learning outcome:

2. Set and install injection pump to engine.
Learning Activity:

2.1 Explaining the operating principles of diesel engine.

Internal Combustion Engines
Engine is a machine that converts heat energy into mechanical energy. The heat from burning
a fuel produces power which moves the vehicle. Automotive engines are internal combustion
(IC) engines because the fuel that runs them burned internally, or inside the engine. There are
two types, reciprocating and rotary. Reciprocating motion means, moving up and down or back
and forth of the piston. Most automotive engine is reciprocating. They have pistons that move
up and down, or reciprocate in cylinders. These are piston engines. Rotary engine has rotors
that spin, or rotate. The only such engine now used in automobiles is the Wankel engine.

Two kinds of piston engines
1. Spark-ignition engine (Gasoline)
2. Compression-ignition (Diesel) engine.

The differences between them are:
1. The type of fuel used
2. The way the fuel gets into the cylinder
3. The way the fuel is ignited

The spark-ignition engine usually runs on a liquid fuel such as gasoline or alcohol blend. The
fuel must be highly volatile so that it vaporizes. This forms the highly combustible air-fuel
mixture that burns easily. The mixture then enters the cylinders and is compressed. Heat from
electric spark produced by the ignition system sets fire to, or ignites, the air-fuel mixture. As the
mixture burns (combustion), high temperature and pressure are produced in the cylinder. This
high pressure, applied to the top of the piston forces it to move down in the cylinder. The
motion is carried by gears and shafts to the wheels that drive the car. The wheel turn and the
car moves.

In the diesel or compression-ignition engine, the fuel mixes with air after it enters the engine
cylinders. The piston compresses the air to as little as 1/22 of its original volume. Compressing
the air this much raises its temperature to 1000F (538C) or higher. A light oil called diesel fuel
is then sprayed or injected into the hot air. The hot air or heat compression ignites the fuel.

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Sept. 20, 2010 1

Information Sheet 2.1.1: Explain the operating principles of diesel engine

Diesel engines are similar to spark- Figure 2.1 shows the construction of two-
ignition engines in construction. Both stroke cycle engine
have pistons, with piston rings, moving
up and down in cylinders. Both burns
fuel in combustion chambers in the
upper part of the cylinders. The high
pressure produced by the burning fuel
pushes the pistons down. This rotates
the crankshaft and the rotary motion is
carried through shafts and gears to the
drive wheels.

Engine Classification by Cycles

Two stroke cycle engine – required
one complete turn of the crankshaft to
accomplish one series of operation
These are intake, compression, power
and exhaust strokes combined. In two-
stroke-cycle. There is power in every
one full crankshaft revolution 360
degrees. See figure 2.1.

Four stroke cycle engine - required
two complete turns of the crankshaft
to accomplish one series of operation.
These are intake, compression,
power, and exhaust stokes. There is
power in every two full crankshaft
revolution 720 degrees. See figure 2.2

Figure 2.2 shows the construction of
four stroke cycle engine

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 2.1.1: Explain the operating principles of diesel engine

The action in the compression-ignition
engine can be divided into four parts
each part consists of piston stroke.
Piston stroke – is the movement of
piston from BDC to TDC to BDC.

Top Dead Center (TDC) - the end point Figure 2.3 shows the TDC and BDC
is reached by the piston head at the top
of the cylinder see figure 2.3.

Bottom Dead Center (BDC) - the end
point is reached by the piston head, at
the lower part of the cylinder see figure
2.3.

Cycle – means a series of events that
repeat themselves.

Diesel Engine Operation

Figure 2.4 and table 2.1 shows the four pistons strokes in a four-stroke cycle diesel engine.

1. INTAKE STROKE. The diesel engine takes in air alone. No throttle valve impedes the
airflow. Intake valve in the cylinder head open allowing pressurized air to enter each
cylinder while piston is travelling downward. The pressurized air supply is made possible by
turbocharger which pushes air into the intake system giving the diesel engine a boost of air
to keep up with instantaneous injection of fuel.

2. COMPRESSION STROKE. The upward-moving piston compresses air alone. When the
piston starts to move upward the valves close which traps the intake air in the cylinder and
allows compression to take place. The heat compression is reached when the piston
reaches the top of the cylinder; the diesel fuel is then injected into cylinder at the precise
time.

3. POWER STROKE. A light oil called diesel fuel is sprayed (injected) into the compressed
hot air. The heat compression ignites the fuel. After injection takes place, an explosion
occurs in the cylinder because of the combination of heat and atomized diesel fuel. This
causes the piston to be forced downward which produces torque and the horsepower
required from a typical diesel engine.

4. EXHAUST STROKE. The exhaust stroke is the same for both engines. The exhaust valve
opens and the burned gases flow out as the piston moves up the cylinder.

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 2.1.1: Explain the operating principles of diesel engine

Figure 2.4 shows the four-piston strokes in a four-stroke-cycle diesel engine.

Diesel Engine Characteristics

The diesel engine has the following characteristics:

1. No throttle valve (except some engines with the pneumatic governor).
2. Compresses only air on the compression stroke.
3. Heat of compression ignites fuel as it sprays into the engine cylinders.
4. Has a high compression ratio of 16:1 to 22:1.
5. Have glow plugs or an electric intake-manifold heater to make starting easier
6. Controls engine power and speed only by the amount of fuel sprayed into the cylinders.

More fuel equals more power.

Table 2.1 shows the relationship of valve and piston movement

PISTON PISTON VALVE POSITION
STROKE MOVEMENT
INTAKE EXHAUST DEGREES
Intake Downward 180
Compression Upward Open Closed 180
Power Downward 180
Exhaust Upward Closed Closed 180
720 degrees
Closed Closed

Closed Open

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Information Sheet 2.1.1: Explain the operating principles of diesel engine

Diesel Fuel

Diesel engines burned diesel fuel. It is light oil made from crude oil by the same refining
process that produces gasoline. The oil must have the viscosity, volatility, and cetane number
for use as a diesel fuel.

1. VOLATILITY. This is a measure of how easily a liquid evaporates. Gasoline vaporizes
easily. It has a high volatility. Diesel fuel has low volatility. It boils at a temperature of about
700ºF [371ºC]. There are two grades of diesel fuel for automotive diesel engines, number 1
diesel and number 2 diesel. Number 1 diesel is more volatile. It is used when temperatures are
very low. Number 2 diesel is the recommended fuel in most automotive diesel engines for most
driving conditions. The less-volatile fuel usually has a higher heating value. When it burns,
more energy is available than from a fuel with higher volatility.

2. VISCOSITY. This refers to a liquid’s resistance to flow. The lower the viscosity the more
easily the liquid flows. Diesel fuel must have a relatively low viscosity. It must flow through the
fuel-system lines and spray into the engine cylinders with little resistance. Oil with high
viscosity will not break into fine particles when sprayed. Large particles burn slowly resulting in
poor engine performance. If viscosity is too low, the oil will not lubricate the moving parts in the
injection pump and injection nozzles. Damage may result. Number 2 diesel has the right
viscosity for most driving conditions. Number 1 diesel has lower viscosity so it will flow and
spray properly at low temperatures. The owner’s manual gives the proper fuel or blend to use
for the conditions.

Cetane Number

The cetane number refers to the ease with which
diesel fuel ignites. A high cetane number means
the fuel is fast burning and ignites easily at a
relatively low temperature. A low cetane number
means the fuel is slower burning and requires a
higher temperature to ignite.

Diesel fuel with a low cetane number takes a little
longer to ignite. This may cause excessive ignition
lag. During this slight delay, the fuel collects in the
cylinder. When ignition does occur, all the fuel
ignites at once. The pressure goes up quickly and
combustion knock results. This is similar to spark
knock or detonation in a spark-ignition engine see
figure 2.5.

High cetane fuel ignites as soon as it enters the Figure 2.5 The higher the cetane number of
cylinder. the diesel fuel, the faster the fuel burns. The
higher the octane number of gasoline, the
There is no accumulation of fuel. The result is a slower it burns.
smooth pressure rise so no combustion knock
occurs.

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Information Sheet 2.1.1: Explain the operating principles of diesel engine

Engine Measurements

Earlier sections describe torque and power. Following sections describe engine performance
measurements including volumetric efficiency. However, engine performance often depends
on mechanical measurements of the engine. These include bore and stroke, piston
displacement, and compression ratio. The mechanical measurements greatly affect engine
torque and power. They also affect its operating range, or speed.

Bore and Stroke

The size of an engine is given by its bore and stroke. The bore is the diameter of the cylinder
see figure 2.6. The stroke is the distance the piston travels from BDC TO TDC. The bore is
always given first. For example, in 4- by 3 ½ -inch cylinder, the bore is 4 inches and the stroke
is 3 ½inches. These measurements are used to figure piston displacement. An engine with a
large bore than stroke is “over square.” A “square” engine has a bore and stroke of equal size.
There are several reasons for square and over square engines. A shorter stroke has less
friction loss. The pistons and rings move shorter distances. The shorter stroke reduces the
load on the engine bearings. The shorter stroke also reduces engine height. The car can have
a lower hood line. Manufacturers have lengthened the stroke in some engines to reduce
exhaust emissions. This gives a longer time for the air-fuel mixture to burn. The result is more
complete combustion and cleaner exhaust gas.

Figure 2.6 shows the stoke and bore of an engine

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Information Sheet 2.1.1: Explain the operating principles of diesel engine

Piston Displacement
Piston displacement is sometimes called “swept volume.” This is the volume that the piston
displaces or “sweeps out” as it moves from BDC to TDC (Fig. 15-7). For example, the piston
displacement in a 4- by 3.5-inch (101.6 by 88.9 mm) cylinder is the volume in a cylinder 4
inches in diameter and 3.5 inches long. To find the piston displacement of this cylinder, use the
formula

ῆ x D² x L³ = 3.14 x 4² x 3.5
44

PD = 3,14 x 16 x 3.5 = 43.96 cubic inches (in.³)
4

Suppose the engine has eight cylinders. The total displacement is 43.96 times 8, or 351.68
cubic inches. The engine is a 351.68 cubic inch displacement (CID) engine. The displacement
is rounded off to “351”.

Displacement is given in the metric system in cubic centimeters (cc) or liters (L). A 200 CID
engine has displacement of 3277.4 cc. One cubic inch equals 16.39 cc. One liter is 61.02 cubic
inches.

The Wankel engine has rotors instead of pistons. Its displacement is the change in volume as
the rotor moves from maximum volume to minimum. This is the single-chamber capacity

Compression Ratio

The compression ratio (CR) is the measure how much the air-fuel mixture is compressed
during the compression stroke. Compression ratio is found by dividing the volume of the
cylinder and combustion chamber when the piston is at BDC by the volume when the piston is
at BDC by the volume when the piston is at TDC see figure 2.7. The volume with the piston at
TDC is the clearance volume. This is the volume that remains above the piston at TDC.
For example, one engine has cylinder volume of 42.35 cubic inches (694 cc) at BDC. It has a
clearance volume of 4.45 cubic inches (73 cc). The compression ratio is 42.35 divided by 4.45
[694 / 73]. This is 9.5:1. The air –fuel mixture is compressed to 1/9.5 of its original volume
during the compression stroke.

Increasing Compression Ratio

The higher compression ratio, the more air-fuel mixture compressed inside the cylinder. After
ignition, a higher combustion pressure results as the burning gas expands to a greater volume.
This exerts more force on the pistons for a longer part of the power stroke. Each power stroke
produces more power.

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Information Sheet 2.1.1: Explain the operating principles of diesel engine

In 1973, the Environmental Protection
Agency (EPA) issued regulations
requiring the removal of leads (tetraethyl
lead [TEL]) from gasoline. Adding lead to
gasoline allowed higher compression
ratios. The lead prevented spark knock
or detonation. This could seriously
damage an engine. The lead left the
engine in the exhaust gas and polluted
the atmosphere. The leads also damage
some emission-control devices.

Removal of lead from gasoline began in
1975. This caused engine compression
ratios to drop, which reduced engine
power. Newer engine designs have
increased compression ratios. The
average engine compression ratio is
about 8.9:1. This results for development
of lean burn and fast burn combustion.
Swirl-type combustion chambers also
allow higher compression ratio.

Figure 2.7 shows the compression ratio of an engine

Engine Performance Measurements

Volumetric Efficiency

Volume efficiency (VE) is the measure of how completely the cylinder fills with air-fuel mixture
during the intake stroke. The cylinder fills completely (100 percent) when the mixture is drawn
in slowly. In the running engine, the mixture must pass rapidly through narrow openings and
bends in the intake manifold. The mixture also gets heated (from engine heat) and expands.
The intake valve is open only a small fraction of a second (one hundredth of a second high
speed). The cylinders never get completely filled because the time is too short. The heat also
has caused mixture to expand.

Good volumetric efficiency for an engine running at fairly high speed at 80 percent. The VE on
some engines at high speed may drop to 50 percent. This means the cylinders are only half
filled. The decrease in VE is one reason that the engine speed and power do not continue to
increase.

Another action that affects VE is how quickly and easily the burnt gasses exhaust from the
cylinder. Exhaust gases remain in the cylinder after the intake stroke begins to allow less air-
fuel mixture to enter.

There are several ways to improve volumetric efficiency. One is to use larger intake valves.
Another is to use more than one intake valve per cylinder. The use of more than one exhaust
valve improves the removal of the exhaust gas from the cylinder.

Another way to improve engine performance is forced induction. A supercharge. A
Supercharge or a turbocharger pressurizes ingoing air or air-fuel mixture. This forces move air
or air-fuel mixture into the cylinders. Increased engine power is the result.

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Information Sheet 2.1.1: Explain the operating principles of diesel engine

Several design improvements can increase volumetric efficiency. One is to increase valve lift.
This is the distance the valve moves down when it opens. Lift cannot be so great that the
pistons strike the valve.

Tuned intake manifolds and tuned exhaust manifolds improve volumetric efficiency. “Tuning”
the passages or runners means to design their length and diameter for the desired
performance. Then the runners in the intake manifold deliver the same amount of air or air-fuel
mixture to each cylinder. Tuning the exhaust manifold in the same way can create a vacuum in
the exhaust system. This helps draw the exhaust gas out of the cylinders and into the exhaust
system.

Engine Torque

Torque is turning force. Engine torque results from the combustion pressures pushing down on
the pistons. When a position is moving down on the power stroke, it applies torque through the
connecting rod to the engine crankshaft. The higher the volume efficiency and the higher the
combustion pressure, the greater the torque.

The pressure in the cylinder drops rapidly as the pistons begins to move down. In some racing
engines, the exhaust valve opens as early as 92 degrees after TDC (88 degrees before BDC).
This causes little power loss because little torque is transmitted to the crankshaft.

The torque for the two valve engine starts high and drops off as engine speed increases. The
four valve engine has a flatter or wider “torque band.” It maintains a high torque output well
past 5000 rpm. This is because the four valves allow the engine to breathe freely even at high
speed.

Engine Power

Engine power is the power available from the crankshaft to do work. The most common unit of
measure for power is the horsepower [hp]. A horsepower is a measure of the rate at which a
horse can work. This is 33,000 ft-lb of work per minute.

The amount of work performed is 33,000 ft-lb (165 feet x 200 pounds). The time is minute. A
horse that did this work in 2 minutes would only be “half” working. It would be producing only ½
horsepower.

Hp = ft-lb per minute = L x W

33,000 33,000 x t

Where;
Hp = horsepower
L = length in feet though which W is exerted
W = force in pounds exerted though the distance L
T = time in minutes required to move W through L

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Information Sheet 2.1.1: Explain the operating principles of diesel engine

In the metric system, engine power output is measured in kilowatts (kW). This is the amount of
electricity an electric generator produces when driven by the engine. One horsepower is equal
to 0.746 kW. One kW is equal to 1.34 hp.
You can calculate horsepower if you know engine torque and speed (rpm). The formula is

hp = torque x rpm / 5252

This formula is used when measuring engine performance with a chassis or engine
dynamometer.

MEASURING HORSEPOWER

Brake horsepower (bhp) is the power available from the engine crankshaft to do work. It is
“brake” horsepower because it is measured with some type of brake. The brake places a load
on the engine crankshaft. Today a dynamometer makes most engine power measurements.
The “dyno” has a built in brake or power absorber to measure the power output of a running
engine.
The engine dynamometer measures engine power when the engine is out of the car. The
power absorber is usually an electric generator or a water brake that connects to the engine
crankshaft. A varying load is placed on the engine by the power absorber. Instruments on the
dynamometer measure brake horsepower and rpm, or torque and rpm. You then use these
readings to calculate horsepower.
Emission and fuel-economy testing require a chassis dynamometer. It can also be used for
trouble-diagnosis and performance testing. The chassis dyno engine measures engine power
with the engine in the vehicle. The drive wheels are placed on the rollers in the floor. The
rollers attach to the power absorber. Instruments usually show either brake horsepower or rpm
or torque rpm. Some chassis dynos provide information on brake action and power-train
operation.

GROSS AND NET HORSEPOWER
Gross horsepower is measured by testing a basic engine. This is an engine stripped except for
the built-in items required to run it. These include the water pump, fuel pump, oil pump, and
built-in emission-control devices.
Net Horsepower is the power delivered by a fully equipped engine. This includes air cleaner,
cooling system, exhaust system, alternator, and all emission controls. Net horsepower is the
power delivered to the transaxle or transmission.
Another horsepower rating is road horsepower. This is the power delivered to the vehicle drive
wheels. It is much less than net horsepower. Power is lost through friction in the transaxle or
transmission and power train. There is also power loss from driving the power-steering pump,
air-conditioning compressor, and other accessories.

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Information Sheet 2.1.1: Explain the operating principles of diesel engine

INDICATED HORSEPOWER
Indicated horsepower (ihp) is the power developed inside the combustion chambers during
combustion. It is determined by measuring the pressure in the engine cylinder. Indicated
horsepower is always higher than brake horsepower. Some of the power developed in the
cylinders is lost in overcoming the internal friction in the engine.

FRICTION HORSEPOWER
Friction horsepower (fhp) is the power required to overcome the friction of the internal moving
parts. A major cause of friction loss is piston-ring friction. It can account for 75 percent of all
friction losses in the engine. Pistons in the short-stroke oversquare engine do not move as far.
Some manufacturers further reduce friction by installing thinner and barrel-faced piston rings.

RELATING BHP, IHP, FHP
Brake horsepower (bhp) is the power available to do work. Indicated horsepower (ihp) is the
power developed in the engine cylinders. Friction horsepower (fhp) is the power lost in
overcoming the internal friction. The relationship is:

Bhp = ihp – fhp

ENGINE EFFICIENCY
The term efficiency means comparing the effort exerted with the results obtained. Engine
efficiency is the relation between its actual power and its theoretical power. This is the power
that would be available if the engine operated without loss. Two types of engine efficiency are
its mechanical efficiency and its thermal efficiency.

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Worksheet 2.1.2: Explain operating principles of diesel engine
Learning outcomes:
2 Set and install injection pump to engine
Learning Activity:
2.1 Explain operating principles of diesel engine

Multiple choice:
Direction: Select the correct answer and write the letter only on your answer sheet
provided for.
1. Diesel engines require more compression than a gas engine because

a. pistons are heavier
b. fuel ignites with spark
c. fuel ignites on intake stroke
d. fuel ignites on compression
2. When air is compressed ____________.
a. it’s cool dense air
b. it is less efficient
c. its density is reduced
d. the temperature increases
3. On a two cycle diesel engine air is supplied by?
a. a blower
b. engine fan
c. cross flow scavenging
d. crankcase scavenging
4. Series of events that repeat themselves in regular sequence is called?
a. Cycle
b. Stroke
c. Combustion
d. Compression
5. The piston movement when travelling from TDC to BDC is called?
a. Cycle
b. Stroke
c. Combustion
d. Compression

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Worksheet 2.1.2: Explain operating principles of diesel engine

6. The highest point of travel of the piston?
a. BDC
b. Cycle
c. Combustion
d. TDC

7. The lowest point of travel of the piston?
a. BDC
b. Cycle
c. TDC
d. Compression

8. Opens and allows exhaust gases to be forced out from engine cylinder.
a. Intake stroke
b. Intake valve
c. Exhaust valve
d. Compression stroke

9. In a 4 cylinder of 4 cycle diesel engine the crankshaft interval between
power strokes of each cylinder.
a. 45 degrees
b. 90 degrees
c. 180 degrees
d. 270 degrees

10. On a 4 cycle diesel engine the injection of fuel begins on
a. exhaust stroke
b. intake stroke
c. compression stroke
d. a few degrees before top dead center

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Worksheet 2.1.2: Explain operating principles of diesel engine

Answers Key:
1. D
2. D
3. D
4. A
5. B
6. D
7. A
8. C
9. C
10. D

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Information Sheet 2.2.1: Explain the operating principles of diesel engine pre-
heating system

Learning outcomes:

2. Inspect injection timing

Learning Activity:

2.2 Explaining the operating principles of diesel engine pre-heating system

Principles of diesel Engine Preheating System

Diesel engine requires a different starting procedure. If the diesel engine is cold, the
intake air must be preheated before cranking the engine. A heating coil in an electric
intake manifold heater or in a glow plug in each pre combustion chamber supplies the
heat.

When the engine is cold, turn the ignition key to on or run. This connects the glow
plugs to the battery so they quickly heat the pre combustion chambers it also turn on a
wait light on the instrument panel. After a few seconds, the pre combustion chambers
are heated sufficiently the glow plugs and wait light turn off.

Glow Plug

Glow plugs- are heating elements that warm the air in the pre combustion chambers
to help start a cold diesel engine as shown in figure 2.0. The glow plugs are threaded
into holes in the cylinder head. The inner tip of the glow plug extends into the pre
combustion chamber. The glow plug housing contains a heat coil inside the tube.
Electrical current flows through the heat coil, heating the tube. The tube has a large
surface area to yield greater heat energy. The space inside the tube is filled with an
insulating material to prevent the heat coil from contacting the inner surface of the tube
when it vibrates.

Figure 2.0 shows the glow plug

There are three types of glow plugs mostly in use up to present are:
1. Conventional type
2. Self temperature-controlling type (which consists of conventional preheating
systems and the new super-glow preheating system);
3. Low-voltage type for conventional super glow system.

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Information Sheet 2.2.1: Explain the operating principles of diesel engine pre-
heating system

SELF-TEMPERATURE-CONTROLLING TYPE GLOW PLUG

In many of the latest Toyota vehicles, self-temperature-controlling type glow
plugs are used. The glow plug has a heater coil, which actually consist of three coils – a
brake coil, balance coil, and a rush coil – hooked up in series as shown in figure 2.1.

When current is applied to the glow plug, the temperature of the rush coils in the
tip of the glow plug first rises, causing the tip of the plug to glow red-hot. Since the
electrical resistance of the balance and brake coils rise sharply as the temperature of
the rush coil rises, the amount of current allowed to pass to the rush coil is consequently
reduced. This is how the plug controls it own temperature. Some glow plugs do not
have a balance coil due to their temperature rise characteristics.

The self-temperature-controlling type glow plugs used in the new super glow
system do not require a current sensor; such was used previously to sense the glow
plug temperature. This permits a more simplified glow system.

Figure 2.1. Cut away of glow plug. Showing the different types of coil

GLOW PLUG CONTROLLER TYPE

DESCRIPTION

The glow plug controller type preheating system consist of the glow plugs, a glow
plug controller, a glow plug relay, etc. the glow plug controller on the instrument panel
indicates when the glow plugs are heating. Below is figure 2.2 showing the electrical
diagram of pre heating.

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Information Sheet 2.2.1: Explain the operating principles of diesel engine pre-
heating system

Figure 2.2 shows the diagram of pre heating system

Preheating circuit consist of;
1. Glow plug relay
2. Starter switch
3. Glow plug controller
4. Glow plug

Glow plug relay- prevents a large flow of current through the starter switch, and
ensures that the voltage drop caused by the glow plug controller does not
effect to the glow plugs.

Starter switch- the current flow causes the glow plugs to heat up, and also cause the
coil in the glow plug controller on the instrument panel to on.

Glow plug controller- located on the instrument panel, monitors the heating of the
glow plugs.

Glow plug- a small electric heater installed in the precombustion chamber of diesel
engines to pre heat the chamber for easer starting in cold weather.

NOTE;
The glow plug indicator light operates independently from the glow plug heating

system and does not indicate whether plugs have actually heated up or not. Therefore,
when trouble shooting in hard starting, the Glow plug should be check one by one even
if the glow indicator is functioning normally.

The rated voltage of the glow plugs differs depending on the battery voltage
usually (12 v or 24 v) and the glow system used.

Heating the glow plugs longer than the specified time may damage the Glow plug
controller.

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Information Sheet 2.2.1: Explain the operating principles of diesel engine pre-
heating system

GLOW PLUG CONTROLLER

The glow plug controller, located on the instrument panel, monitors the heating of the
glow plugs as shown below figure 2.3. It contains a resistor which is connected to the
same power supply and which reddens at the same time as the glow plugs redden.
(Normally, this glow plug controller should redden about 15 – 20 seconds after the
switch is closed.)

Figure 2.3 glow plug indicator

GLOW PLUG RELAY
The glow plug relay prevents a large flow of current through the starter switch,

and ensures that the voltage drop caused by the glow plug controller does not affect the
glow plugs. The glow plug relay actually consist of two relays: when the starter switch is
in the G (glow) position, one of them passes the current through the glow plug controller
to the plugs.
In the start position, the other way passes the current directly to glow plugs but not
through the glow plug controller. This prevents the voltage drop due to the resistor in the
glow plug controller from affecting the glow plugs during cranking.

OPERATION

1. STARTER SWITCH AT “G”
A circuit from the battery (+) terminal » starter switch AM terminal » starter switch

terminal G » glow plug relay terminal g » coil L¹ » ground in formed, causing coil L¹ to
attract and close points P¹. This allows formation of a circuit from the battery (+) terminal
» glow plug relay terminal B » points P¹ » glow plug controller » glow plugs » ground.
The current causes the glow plugs to heat up, and also causes the coil in the glow plug
controller on the instrument panel to glow red, indicating that the glow plugs are heating.

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Information Sheet 2.2.1: Explain the operating principles of diesel engine pre-
heating system

2. STARTER SWITCH AT “START”
A circuit from glow plug relay terminal ST » coil » L² » ground is formed, causing

coil L² to attract and close points P². This allows formation of a circuit from the battery
(+) terminal » glow plug relay terminal B » point P².» glow plug relay terminal S » glow
plugs » ground. At this time, the glow plug controller does not turn on. Please refer to
figure 2.4 the complete diagram of pre-heating.

Figure 2.4 complete pre-heating diagram

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
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Worksheet 2.2.2: Explain operating principles of diesel engine preheating system

Learning outcomes:

2. Set and install injection pump to engine
Learning Activity:

2.2 Explain operating principles of diesel engine preheating system

Multiple Choice:
Instruction: Read the question. Select the correct answer and write the letter on your
answer sheet provided for.

1. Heating coil in an electric intake manifold heater or glow plug in each
precombustion chamber supplies the

a. air
b. current
c. fuel
d. heat

2. When cranking the cold diesel engine the intake air must be
a. compressed
b. enlarged
c. expanded
d. preheated

3. When the ignition key is turn on, the glow plugs is connected and the
battery quickly heat the
a. air
b. fuel
c. oil
d. precombustion chamber

4. The heating element that warm the air in the precombustion chamber
to help start the cold diesel engine
a. drain plug
b. glow plug
c. spark plug
d. vent plug

5. The glow plugs are threaded into holes in the
a. piston
b. cylinder head
c. cylinder block
d. valves

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Worksheet 2.2.2: Explain operating principles of diesel engine preheating system

6. The purpose of preheating system in diesel engine is to
a. minimize fuel consumption
b. minimize oil consumption
c. starting the engine easier
d. starting the engine longer

7. A light is installed in the instrument panelof which the purpose is to inform the
driver that the engine is ready to start
a. oil indicator light
b. glow indicator light
c. pressure indicator light
d. temperature indicator light

8. The type of preheating circuit that prevent a large flow of current through
the starter switch
a. glow plug controller
b. glow plug relay
c. pressure switch
d. starter switch

9. The type of preheating circuit located on the instrument panel, that monitor the
heating of the glow plugs
a. starter switch
b. glow plug relay
c. ignition switch
d. glow plug controller

10. If the glow plug is heating more than in the specified time or limit may cause
damage of the
a. glow plug relay
b. glow plug
c. starter switch
d. glow plug controller

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Worksheet 2.2.2: Explain operating principles of diesel engine preheating system

Answers key
1. d
2. d
3. d
4. b
5. b
6. c
7. b
8. b
9. d

10. d

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Information Sheet 2.3.: Identify the diesel fuel system components and its
function
Learning outcomes:
2. Set and Install injection pump to engine
Learning Activity:
2.3 Identifying components and functions of fuel system

Fuel System

The function of the fuel system is to store and supply fuel to the cylinder chamber
where it can be mixed with air, vaporized, and burned to produce energy. The fuel, which
can be either gasoline or diesel, is stored in a fuel tank. A fuel pump draws the fuel from
the tank through fuel lines and delivers it through a fuel filter to either a carburetor or fuel
injector, then delivered to the cylinder chamber for combustion. Please see figure 2.0.

Figure 2.0 shows a diagram of diesel fuel system

Parts fuel line system 4. Fuel tank
5. Fuel pump
1. Fuel-return line 6. Fuel filter
2. Injection line
3. Fuel supply line

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Information Sheet 2.3.: Identify the diesel fuel system components and its
function

DIESEL

Diesel fuel, like gasoline is a complex blend of carbon and hydrogen compounds.
It too requires additives for maximum performance. There are two grades of diesel fuel
used in automobiles today: 1-D and 2-D. Number 2 diesel fuel has a lower volatility and
is blended for higher loads and steady speeds, therefore works best in large truck
applications. Because number 2 diesel fuel is less volatile, it tends to cause hard
starting in cold weather. On the other hand number 1 diesel is more volatile, and
therefore more suitable for use in an automobile, where there are constant changes in
load and speed. Since diesel fuel vaporizes at a much higher temperature than
gasoline, there is no need for a fuel evaporation control system as with gasoline. Diesel
fuels are rated with a cetane number rather than an octane number. While a higher
octane of gasoline indicates resistance to ignition, the higher cetane rating of diesel fuel
indicates the ease at which the fuel will ignite. Most number 1 diesel fuels have a cetane
rating of 50, while number 2 diesel fuel have a rating of 45. Diesel fuel emissions are
higher in sulfur and lower in carbon monoxide and hydrocarbons than gasoline and are
subject to different emission testing standards.

Diesel Fuel

Diesel engines burns diesel fuel oil. It is light oil made from crude oil by the same
refining process. The oil must have viscosity, volatility, and cetane.

VOLATILITY

This is a measure of how easily a liquid evaporates. Gasoline vaporizes easily
and therefore has high volatility. Diesel fuel has low volatility. It boils at a temperature of
about 700ºF [371ºC]. There are two grades of diesel fuel for automotive diesel engines,
number 1 diesel and number 2 diesel. Number 1 diesel is more volatile. It is used when
temperatures are very low. Number 2 diesel is the recommended fuel in most
automotive diesel engines for most driving conditions. The less-volatile fuel usually has
a higher heating value. When it burns, more energy is available than from a fuel with
higher volatility.

VISCOSITY
This refers to a liquid’s resistance to flow. The lower the viscosity the more easily

the liquid flows. Diesel fuel must have a relatively low viscosity. It must flow through the
fuel-system lines and spray into the engine cylinders with little resistance. Oil with high
viscosity will not break into fine particles when sprayed. Large particles burn slowly
resulting in poor engine performance. If viscosity is too low, the oil will not lubricate the
moving parts in the injection pump and injection nozzles. Damage may result. Number 2
diesel has the right viscosity for most driving conditions. Number 1 diesel has lower
viscosity so it will flow and spray properly at low temperatures. The owner’s manual
gives the proper fuel or blend to use for the conditions.

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Information Sheet 2.3.: Identify the diesel fuel system components and its
function

Cetane Number

The cetane number refers to the ease with
which diesel fuel ignites. A high cetane
number means the fuel is fast burning and
ignites easily at a relatively low
temperature. A low cetane number means
the fuel is slower burning and requires a
higher temperature to ignite.

Diesel fuel with a low cetane number Figure 2.1 The higher the cetane number of
takes a little longer to ignite. This may the diesel fuel, the faster the fuel burns. The
cause excessive ignition lag. During this higher the octane number of gasoline, the
slight delay, the fuel collects in the slower it burns. (Ford Motor Company)
cylinder. When ignition does occur, all the
fuel ignites at once. The pressure goes up
quickly and combustion knock results.
This is similar to spark knock or detonation
in a spark-ignition engine. Please see
figure 2.1

High cetane fuel ignites as soon as it
enters the cylinder.

There is no accumulation of fuel. The result is a smooth pressure rise so no combustion
knock occurs.

FUEL TANK

Tank location and design are always a compromise with available space. Most
automobiles have a single tank located in the rear of the vehicle see figure 2.2. Fuel
tanks today have internal baffles to prevent the fuel from sloshing back and forth. If you
hear noises from the rear on acceleration and deceleration the baffles could be broken.
All tanks have a fuel filler pipe, a fuel outlet line to the engine and a vent system. All
catalytic converter cars are equipped with a filler pipe restrictor so that leaded fuel,
which is dispensed from a thicker nozzle, cannot be introduced into the fuel system. All
fuel tanks must be vented. Before 1970, fuel tanks were vented to the atmosphere,
emitting hydrocarbon emissions. Since 1970 all tanks are vented through a charcoal
canister, into the engine to be burned before being released to the atmosphere. This is
called evaporative emission control and will be discussed further in the emission control
section. Federal law requires that all 1976 and newer cars have vehicle rollover
protection devices to prevent fuel spills.

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Information Sheet 2.3.: Identify the diesel fuel system components and its
function

Figure 2.2 shows fuel tank
FUEL LINES

Steel lines and flexible hoses carry the fuel from the tank to the engine. When
servicing or replacing the steel lines, copper or aluminum must never be used. Steel
lines must be replaced with steel, please see figure 2.3. When replacing flexible rubber
hoses, proper hose must be used. Ordinary rubber such as used in vacuum or water
hose will soften and deteriorate. Be careful to route all hoses away from the exhaust
system.

Figure 2.3 Example of fuel pipe

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Information Sheet 2.3.: Identify the diesel fuel system components and its
function

FUEL PUMPS
Two types of fuel pumps are used in automobiles; mechanical and electric. All

fuel injected cars today use electric fuel pumps, while most carbureted cars use
mechanical fuel pumps. Mechanical fuel pumps are diaphragm pumps, mounted on the
engine and operated by an eccentric cam usually on the camshaft. A rocker arm
attached to the eccentric moves up and down flexing the diaphragm and pumping the
fuel to the engine. Because electric pumps do not depend on an eccentric for operation,
they can be located anywhere on the vehicle. In fact they work best when located near
the fuel tank.

Many cars today, locate the fuel pump inside the fuel tank. While mechanical
pumps operate on pressures of 4-6 psi (pounds per square inch), electric pumps can
operate on pressures of 30-40 psi. Current is supplied to the pump immediately when
the key is turned. This allows for constant pressure on the system for immediate
starting. Electric fuel pumps can be either low pressure or high pressure. These pumps
look identical, so be careful when replacing a fuel pump that the proper one is used.
Fuel pumps are rated by pressure and volume. When checking fuel pump operation,
both specifications must be checked and met. Fuel pump can be mounted on the
engine block, which is lift fuel from the tank to the injection system please see fegure2.4
below.

Figure 2.4 shows the cut away of fuel pump

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Information Sheet 2.3.: Identify the diesel fuel system components and its
function

FUEL FILTERS

The fuel filter is the key to a properly functioning fuel delivery system. This is
more true with fuel injection than with carbureted cars. Fuel injectors are more
susceptible to damage from dirt because of their close tolerances, but also fuel injected
cars use electric fuel pumps. When the filter clogs, the electric fuel pump works so hard
to push past the filter that it burns itself up. Most cars use two filters. One inside the gas
tank and one in the fuel line to the fuel injectors or carburetor. Unless some severe and
unusual condition occurs to cause a large amount of dirt to enter the gas tank, it is only
necessary to replace the filter in the line please see figure 2.5. Filter, is used to remove
abrasive particles and water.

Figure 2.5 shows fuel filter

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Information Sheet 2.3.: Identify the diesel fuel system components and its
function
FUEL RETURN LINES

In an automobile, fuel return lines are used to keep a minimum amount of flow
through the fuel system and a pressure regulator (or fuel controller) is used to control
the fuel system pressure. It maintains a certain pressure/flow by passing some flow
from the injector rails back to the fuel tank. Figure 2.6 shows return line back to the fuel
tank. This means there is always fuel flow through the return line.

Figure 2.6 shows the return line back to fuel tank

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Information Sheet 2.3.: Identify the diesel fuel system components and its
function

INJECTION LINE
A common rail fuel injection system for a diesel engine, said fuel injection system

comprising; a high pressure fuel pump operative to supply high pressure fuel for
Fuel Injection, a double walled fuel line having an inner tube defining a high pressure
Fuel passage connected to receive high pressure fuel from the fuel pump please see
figure 2.7 below and the outer defining a low pressure return fuel passage surrounding
the high pressure passage ; a series of fuel injectors communicating with the low
pressure passage to deliver low pressure to return fuel for reuse in the system; and a
pressure sensor operative to detect changes in fuel pressure in the pressure passage
for in indicating fuel leaks in either of the high and low pressure fuel tubes.

Figure 2.7 High pressure lines

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Worksheet 2.3.2 Identify the diesel fuel components and its functions

Learning outcomes:
2. Set and install injection pump to engine
Learning Activity:
2.3 Identifying the diesel fuel components and its functions

Multiple Choice:
Instruction: Select the correct answer and write the letter on your answer

sheet provided for.

1. What maintains a certain pressure/flow by passing some flow of fuel from the
injector rails back to the fuel tank_____?
a. fuel filter
b. fuel tank
c. fuel-return line
d. fuel supply line

2. A high pressure mechanical pump that meters the amount of fuel and delivers to
each injector nozzle at the right time
a. carburetor
b. fuel filter
c. fuel pump
d. injection pump

3. A device used to lift fuel from the tank to the injection system called?
a. injector
b. rotor
c. fuel filter
d. fuel pump

4. Which one of the following is NOT a component of diesel fuel system?
a. Fuel filter
b. Fuel line
c. Throttle valve
d. Fuel-return line

5. A part of fuel system that is use to remove abrasive particles and water .
a. camshaft
b. feed pump
c. filter
d. plunger

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
ALT723301
Nov. 28, 2003 Sept. 20, 2010 1

Worksheet 2.3.2 Identify the diesel fuel components and its functions

6. A device that carries the fuel from the tank to the engine is called?
a. filter
b. fuel line
c. injection pump
d. water pump

7. Which one of the following is a part of diesel fuel system?
a. chamber
b. heater
c. glow plug
d. injection line

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
ALT723301
Nov. 28, 2003 Sept. 20, 2010 2

Worksheet 2.3.2 Identify the diesel fuel components and its functions

ANSWERS KEY
1. c
2. D
3. D
4. C
5. C
6. B
7. C

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
ALT723301
Nov. 28, 2003 Sept. 20, 2010 3