Cylinder Compression Pressure Test
• The result of a cylinder compression pressure test can be utilized to diagnose several engine malfunctions.
• Ensure the battery is completely charged and the engine starter motor is in good operating condition. Otherwise
the indicated compression pressures may not be valid for diagnostic purposes.
− Check engine oil level and add oil if necessary.
− Disconnect the spark plug wires.
− Remove all spark plugs from engine (as spark plugs are being removed, check electrodes for abnormal
firing indicators fouled, hot, oily, etc.).
− Record cylinder number of each spark plug for future reference.
− Disconnect fuel injector electrical connectors.
− Be sure throttle blade is fully open during the compression check.
− Insert compression pressure adaptor or the equivalent into each spark plug hole in cylinder head.
− Crank engine until maximum pressure is reached on gauge. Record each cylinder pressure.
− Compression should not be less than 1000 kPa and not vary more than 25 percent from cylinder to cylinder.
− If one or more cylinders have abnormally low compression pressures, repeat the compression test.
− If the same cylinder or cylinders repeat an abnormally low reading on the second compression test, it could
indicate the existence of a problem with the cylinder in question.
NOTE :
The recommended compression pressures are to be used only as a guide to diagnosing engine problems. An engine
should not be disassembled to determine the cause of low compression unless some malfunction is present.
Cylinder Head Gasket Test
• A cylinder head gasket leak can be located between adjacent cylinders, between a cylinder and the adjacent
water jacket or from an oil passage to the exterior of the engine.
• Possible indications of the cylinder head gasket leaking between adjacent cylinders are:
− Loss of engine power
− Engine misfiring
− Poor fuel economy
• Possible indications of the cylinder head gasket leaking between a cylinder and an adjacent water jacket are:
− Engine overheating
− Loss of coolant
− Excessive steam (white smoke) emitting from exhaust
− Coolant foaming
DIAGNOSIS & TESTING