Performing Diesel Engine Tuneup

Job Sheet 4.1.1: Perform the procedures in bleeding injection system components

6. At this time, tighten the air bleed plug on the filter.
7. Slowly loosen the air bleed plug on the injector pump, letting air escape until an air free

flow of fuel is evident. Units with a self bleed return valve, open for a short period then
start engine, as soon as engine runs smooth close valve. Model-12 has continuous fuel
bleeding.
8. At this time, tighten the air bleed plug or knurled knob on the injector pump.
9. The fuel system should now be properly bled and ready for operation.

Refer to starting instructions before attempting to start the engine after bleeding the fuel
system.
CAUTION: Excessive cranking with seal cock valve open can cause water accumulation in
the muffler and possibly back up into the engine. Drain muffler as needed.

FUEL INJECTORS:
Fuel injectors should be removed and taken to a qualified diesel engine repair center to be
tested for leakage and spray pattern, if poor engine performance such as loss of power,
rough or uneven running, sudden notice of dark exhaust, or engine becomes hard to start.

REMOVING INJECTORS:
1. Clean the area around the injectors before removing.
2. Loosen nuts holding fuel lines to injector pump and injector nozzle and remove fuel

lines.
3. Loosen nuts on return line adapters and remove adapters.
4. Loosen injectors and remove injectors.

REPLACING INJECTORS:

1 Check to be sure contact surfaces and area around injectors is clean.

2. Replace injectors in the same cylinder from which they were removed.

3. Torque required to properly seat the injectors will be between 43 and 58 ft./lbs.

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

Job Sheet 4.1.1: Perform the procedures in bleeding injection system components

4. Replace fuel return lines and secure nuts.

5. Replace all fuel lines and secure all nuts.

6. After all injectors, fuel lines and hoses have been replaced and are secured; the fuel
system will have to be bled.

The fuel injection pump has been set at the factory and should need no adjustment. Any
apparent problem with the pump should be referred to a qualified diesel mechanic or to a
Universal Diesel dealer as advised.
NOTE: NO WARRANTY COVERAGE WILL BE GRANTED IF ANY OF THE FACTORY
SET AND SEALED FUEL AND MAXIMUM RPM. ADJUSTMENTS ARE ALTERED.

Code No. Perform Diesel Engine Tune Up Date: Developed Date: Revised Page #
ALT723301
Nov. 28, 2003 Sept. 20,2010 4

Job Sheet 5.1.1 : Perform procedures in conducting compression testing of diesel
engine
Learning outcomes:

9. Conduct compression test

Learning Activity:

9.1 Performing procedures in conducting compression testing of diesel engine

The cylinder compression tester (figure 5.0) measures the ability of the cylinders
to hold compression while the starting motor cranks the engine. The 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.

Fig. 5.0 Compression tester

HINT: If there is a lack of power, excessive oil consumption, or poor fuel economy,
measure the compression pressure.

Procedures (Steps)

1. Prepare the supplies, materials, tools and equipment
2. Warm up the engine to operating temperature.
3. Stop the engine.
4. Disconnect the wire from the fuel shutoff solenoid terminal of the injection pump.

This prevents the delivery of fuel during the test.

Code No. Date: Developed Date: Revised Page #
ALT723301 PERFORM DIESEL ENGINE TUNE UP Sept. 20, 2010 1

Nov. 28, 2003

Job Sheet 5.1.1 : Perform procedures in conducting compression testing of diesel
engine

Shutoff solenoid
terminal

5. Remove glow plugs
6. Screw the SST attachment into the glow plug hole.
7. Connect the compression gauge SST to the SST attachment.

8. Set the engine speed control to stop position.

9. Turn the engine with the starter until the pressure gauge registers no further rise in
pressure.

Code No. Date: Developed Date: Revised Page #
ALT723301 PERFORM DIESEL ENGINE TUNE UP Sept. 20, 2010 2

Nov. 28, 2003

Job Sheet 5.1.1 : Perform procedures in conducting compression testing of diesel
engine

Note: It is a good practice to count the number of compression strokes, indicated
by movement of the gauge needle, and check each cylinder with the same
number of strokes. The engine must be at full cranking speed or as specified in
appropriate service manual to get a good reading.

10. Check the pressure reading against the engine technical manual.

Note: Low pressure indicates leakage through valves, rings or gaskets.
Variations in cylinder pressures of more than 10% usually indicate a need for
cylinder reconditioning.

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.

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.

Code No. Date: Developed Date: Revised Page #
ALT723301 PERFORM DIESEL ENGINE TUNE UP Sept. 20, 2010 3

Nov. 28, 2003

Job Sheet 5.1.1 : Perform procedures in conducting compression testing of diesel
engine

If the compression pressure increases to a Compression Gauge Possible Engine
more normal value, the low compression
probably is due to leakage past worn Reading Condition
piston rings. Other possible causes are a
worn piston or cylinder wall, and rings that Fails to climb during Valve sticking open
are broken or stuck in their piston-ring all compression
grooves. Refer to table 5.0 strokes

20 PSI (138 kPa) Faulty rings or valve
below normal seating

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

Table 5.0 Compression-gauge readings and
the probable engine conditions.

Possible Causes:

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.

I therefore recommend that if below the minimum specified
compression pressure the Engine, will be subjected to General Engine
Overhaul.

Code No. Date: Developed Date: Revised Page #
ALT723301 PERFORM DIESEL ENGINE TUNE UP Sept. 20, 2010 4

Nov. 28, 2003

Worksheet 5.1.2: Conduct compression testing of a diesel engine

Learning outcomes:
5. Conduct compression testing
Learning Activity:
5.1 Conducting compression testing of a diesel engine

Instruction :
1. Perform compression testing
2. Write down the results for each cylinder

Dry test: Cylinder no. 2 Cylinder no. 3 Cylinder no. 4
Cylinder no. 1

Wet test: Cylinder no. 2 Cylinder no. 3 Cylinder no. 4
Cylinder no. 1

Recommendation:

______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
____________________

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