ENGINE MECHANICAL
SERVICE MANUAL NUMBER 22
Page 3A-30
90-860074--1 FEBRUARY 2002
Compression Testing Procedure
Periodically check engine compression pressure. Lowering of pressure causes loss of
power, greater fuel consumption, smoke at the exhaust, low acceleration, unsteady slow
idle, difficulty in starting and bearing seizure because of engine overheating.
1. Refer to SECTION 5C - Fuel Injectors, and while observing precautions listed, remove
all fuel injectors.
IMPORTANT: To achieve the cranking rpms needed (300 rpm minimum) for a proper
compression test, it will be necessary to remove all of the injectors prior to testing.
2. Clean injector bore and install Compression Tester Adapter Tool 91-881737.
3. Torque the injector clamp to 24 Nm (18 lb-ft).
4. Connect gauge to Compression Adapter Tool and set gauge to zero.
5. Ensure that battery is fully charged.
6. Operate the starter. The engine should be cranking at approximately 300 rpm. Check
compression gauge reading. Compression should be 30-32 bar (435-464 psi).
Maximum pressure difference between cylinders should not exceed 500 kPa (72 psi).
7. Readings lower than specified, or differences between cylinders greater than specified,
indicate engine problems may exist (such as faulty rings, valves, cylinders and pistons).
Repair as needed.
8. If readings are within specifications, refer to SECTION 5C - Fuel Injectors, and install
injectors in heads from which removed previously.
9. Purge air from injectors. Refer to SECTION 5C - Fuel Injectors.
