Performing Diesel Engine Tune Up

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 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 LO7-2 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 LO4-2. 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

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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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ASSESSMENT TASKS:

These assessment tasks should be completed when you are confident that you can
check/replace fuel filter and air cleaner. 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

Compression test is performed properly.

Results of compression tests are reported to
instructor.

Engine components are cleaned.

Tools are properly used and stored.

Work area is cleaned.

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PERFORMANCE TEST

Learner's Name Date
Competency: Perform Diesel Engine Tune Up
Test Attempt
1st 2nd
3rd

Directions: OVERALL EVALUATION

CALL YOUR INSTRUCTOR, ask Level PERFORMANCE LEVELS
your instructor to assess your Achieved
performance in the following critical
task and performance criteria 4 - Can perform this skill without supervision
below. and with initiative and adaptability to problem
situations.
You will be rated based on the
overall evaluation on the right side. 3 - Can perform this skill satisfactorily without
assistance or supervision.

2 - Can perform this skill satisfactorily but
requires some assistance and/or supervision.

1 - Can perform parts of this skill satisfactorily,
but requires considerable assistance and/or
supervision.

Instructor will initial level achieved.

PERFORMANCE STANDARDS Yes No N/A
For acceptable achievement, all items should receive a "Yes" or "N/A"
response.

1. Setting/installation of injection pump is performed in
accordance with manufacturer’s manual specifications

2. Timing marks and torque and injection pump moving parts
are checked before installation.

3. Mounting bolts are tightened following torque as stated in the
manual of specifications.

4. No error in detecting and reading injection timing.
5. Injection pump timing device is used without error.
6. Injection pump timing result is interpreted correctly.
7. Advance timing operation is checked.
8. Fuel level, line leakage and fuel strainer or filters are

checked.

9. Air lock in the system is determined without error.

10. Bleeder screw and prime pump is determined and used
properly.

11. Procedures on bleeding injection system are followed guided
by the service manual.

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Learner’s diary

DIARY NOTES

Record important dates, jobs undertaken and other workplace events that will assist you in providing
further details to an Assessor.

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Record of Achievement

Module # 1: Performing Diesel Engine Tune Up

LO 1 : Set and install injection pump to engine

Performance Criteria:

1.1. Setting/installation of injection pump is performed in accordance with
manufacturer’s manual specifications.

1.2. Timing marks and torque and injection pump moving parts are checked before
installation.

1.3 Mounting bolts are tightened following torque as stated in the manual of
specifications.

1.4 No error in detecting and reading injection timing.

Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
Trainer’s signature:.......................................................................
Date:.............................................................................................

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Record of Achievement

Module # 1: Performing Diesel Engine Tune Up

LO 2 : Inspect injection timing

Performance Criteria:

2.1 Injection pump timing device is used without error.
2.2. Injection pump timing result is interpreted correctly.
2.3. Advance timing operation is checked.

Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
Trainer’s signature:.......................................................................
Date:.............................................................................................

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Record of Achievement

Module # 1: Performing Diesel Engine Tune Up

LO 3 : Bleed injection system components

Performance Criteria:

3.1. Fuel level, line leakage and fuel strainer or filters are checked.
3.2. Air lock in the system is determined without error.
3.3 Bleeder screw and prime pump is determined and used properly.
3.4 Procedures on bleeding injection system are followed guided by the service

manual.

Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
Trainer’s signature:.......................................................................
Date:.............................................................................................

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Record of Achievement

Module # 1: Performing Diesel Engine Tune Up

LO 4 : Conduct compression testing

Performance Criteria:

4.1. Engine requirements in compression testing is set and prepared.
4.2. Read and interpreted specific compression test result.
4.3 Corresponding recommendation/prescription is given based on test result.

Comments:
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Learner has satisfied the above performance criteria.
Learner’s signature:......................................................................
Trainer’s signature:.......................................................................
Date:.............................................................................................

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Terms and Definitions

Bleeding a system:
Remove air bubbles from a brake system, a fuel injection system, or a cooling
system so that they won't impede the flow of liquid through that system.

Cetane number:
A method of rating diesel oil or fuel by measuring the time lapse between fuel
injection and ignition to determine how easy it is to ignite and how fast it will
burn. The lower the cetane number, the higher the temperature required to burn
the oil.

Compression:
[1] Applying pressure to a spring, or any springy substance, thus causing it to
reduce its length in the direction of the compressing force.
[2] Applying pressure to a gas, thus causing a reduction in volume.
[3] One of the essential factors in a internal combustion engine (fuel, air, proper
proportion of mixture, compression, timing, spark). It is the squeezing of the
fuel-air mixture in the cylinder of a spark-ignition engine or the squeezing of the
air in a diesel engine. Compression makes the process of combustion more
effective and increases engine efficiency.
[4] Term used to denote increase of pressure on a fluid by using mechanical
energy.
[5] Reduction in volume and increase in pressure and temperature of a gas
caused by squeezing it into a smaller space

Compression tester:
A device which is screwed or pushed into the spark plug hole so that when the
engine is turned over, it measures the amount of compression in that cylinder.

Delivery lines:
Fuel lines used to carry fuel from the fuel injection pump to the injector nozzles

Delivery valve:
[1] The valve on the outlet side of a pump.
[2] A fuel injection pump valve that rapidly decreases injection line pressure to
achieve an abrupt fuel cutoff at the injector

Diesel engine:
An internal combustion engine that uses diesel oil for fuel. The true diesel does
not use a carburetor or an ignition system (i.e., spark plugs) but injects diesel oil
into the cylinders when the piston has compressed the air so tightly that it is hot
enough to ignite the diesel fuel without a spark. Because a cold engine cannot
ignite the diesel fuel, glow plugs are used to heat the mixture, but they do not
provide a spark. Named after Rudolf Diesel (1858-1913), the inventor.

Diesel fuel:
A light oil fuel which has a relatively low ignition temperature.

Fuel filter:
A device that removes impurities from the fuel before it gets to the carburetor. It

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is usually found near the carburetor in the fuel line that comes from the fuel
pump (in-line fuel filter), or inside the carburetor (integral fuel filter) or fuel pump
(integral fuel filter). This unit must be cleaned or replaced on a regular basis,
usually once a year or it will become clogged and restrict fuel to the carburetor.
Without a filter, the jets and orifices in the carburetor will become clogged.

Idler gear:
A gear that is placed between two other gears to reverse the direction of
rotation of the output gear.

Ignition:
A process which initiates the combustion of the compressed air/fuel mixture in
the combustion chamber. In a spark-ignition engine, the mixture is ignited by an
electric spark; in a diesel engine, the self-igniting mixture must be preheated by
glow plugs when a cold start is performed.

Injection fuel:
In Bosch CIS, the pressure of the fuel in the lines between the differential-
pressure valves and the injectors. Also called injector pressure.

Injection pump:
A pump which receives fuel from the fuel tank (often through the fuel-feed pump
in the case of diesel engines) and delivers it under pressure to the injectors.

Injection pump governor:
Device which controls fuel deliver to limit the minimum and maximum engine
speeds, as well as intermediate throttle positions.

Injector opening pressure:
The point at which injection pump fuel pressure overcomes nozzle valve-spring
resistance, or combustion chamber pressure, so that fuel is injected into the
pre-combustion chamber.

Injector:
Refers to the pump system (used in a fuel injection system) that squirts or
injects a measured amount of gasoline into the intake manifold in the vicinity of
the intake valve. In the diesel engine fuel is injected directly into the cylinder. In
a Continuous Injection System (CIS), the injectors atomize the continuous flow
of fuel injected under pressure into the intake ports of the engine; a valve in the
injector nozzle stops the flow of fuel when fuel pressure drops below a certain
point; in a CIS, the quantity of fuel is regulated by the fuel distributor's metering
unit; in other fuel injection systems, the fuel system delivers a constant supply of
fuel at a constant pressure to the injector, and an electronic sensing and control
system produces electrical current pulses of appropriate duration to hold open
the injector solenoid valves; as fuel pressure is held constant, varying the pulse
duration increases or decreases the amount of fuel passed through the
injectors.

Injector nozzle:
The tip of the injector, either of multi-hole design for direct injection or pintle
design for indirect injection.

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Nozzle:
A thin hollow tube; a jet or hole at the end of a pipe.

Pneumatics:
The study of pressure and flow in gases. A pneumatic drill is operated by
compressed air; a pneumatic tire contains compressed air.

Timing:
One of the essential factors in a internal combustion engine (Fuel, Air, Proper
proportion of mixture, compression Timing, spark). When the piston is in the
compression stroke both valves must be closed. If one or more is open, the
valve timing is out. Perhaps a timing belt or timing chain has jumped a tooth. If
the spark does not arrive at the correct moment, the engine is out of time. If this
ignition timing is only slightly off, the engine may run with less efficiency.

Timing marks:
[1] Marks or notches, usually located on the vibration damper used to
synchronize the ignition system so that the plugs will fire at the precise time.
[2] One tooth on either the camshaft or crankshaft gear will be marked with an
indentation or some other mark. Another mark will be found on the other gear
between two of the teeth. The two gears must be meshed so that the marked
tooth meshes with the marked spot on the other gear.

Vacuum pump:
A diaphragm type of pump used to produce a vacuum.
A special high efficiency device used for creating high vacuums for testing or
drying purposes.
A mechanical device used to evacuate an air conditioning system to rid it of
moisture, air, and contaminants.

Viscosity:
[1] A measure of an oil's ability to pour or be thick. Every container of oil is
marked with the viscosity of the oil. Straight weight (also called "single viscosity"
or "single weight") oil has a single number like 30 weight. A lower number
means the oil is thinner and is particularly good for lower temperatures. A higher
number is better for hotter temperatures. Multigrade (also called "multiviscosity"
or "multiweight") oil has two numbers like 10W40. When the temperature is low,
a multigrade oil like 10W40 will act like a 10 weight oil; but when the
temperature increases, it will act like a 40 weight. In this way, a multigrade oil is
excellent for all-around driving.
[2] Comparative fluidity or stiffness of liquid adhesives, coatings, and sealers.
[3] Measurement of thickness of oil or its resistance to flow. Also see spraying
viscosity

Volatility:
The property of gasoline, alcohol, etc., to evaporate quickly and at relatively low
temperatures. For instance, gasoline is more volatile (has higher volatility) than
kerosene because it evaporates at a lower temperature.

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