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Cylinder Compression Test

NOTE:

Do not attempt to use a remote starter switch when testing a MULTI-AIR equipped engine, the ignition MUST remain in the "key on" position. If the ignition is in the "off" position, the intake valves will not actuate and the result will be no compression. 

NOTE:

The results of a cylinder compression pressure test can be utilized to diagnose several engine malfunctions.

NOTE:

Be certain 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 diagnosis purposes.

  1. If possible, for best results, the compression test should be performed on a warm engine.
  2. Remove the Fuel Pump Motor fuse from the power distribution center. Refer to FUSE - RELAY LOCATIONS AND TYPES, SPECIFICATIONS .
  3. Start and run the engine until it stalls.
  4. Attempt to restart the engine a few times until the engine will no longer start.
  5. Remove the spark plugs and record the cylinder number of each spark plug for future reference. Refer to SPARK PLUG, REMOVAL AND INSTALLATION .
  6. Inspect the spark plug electrodes for abnormal firing indicators such as fouled, hot, oily, etc.
  7. Install a compression pressure gauge following the manufacturer's instruction.
  8. Crank the engine using the ignition key or by pressing the start button.
  9. The pressure should build quickly for the first three revolutions and reach a maximum after about 5 to 7 revolutions, record the maximum compression gauge pressure. Continue the test for the remaining cylinders.
    NOTE:

    The Compression Pressure specification should only be used as a guide to diagnose engine problems. Refer to TECHNICAL SPECIFICATIONS . An engine should not be disassembled to determine the cause of low compression unless some malfunction is present.

  10. If one or more cylinders have abnormally low compression pressures, repeat the compression test.
    NOTE:

    If the same cylinder or cylinders repeat an abnormally low reading on the second compression test, it could indicate the existence of a problem in the cylinder in question.

  11. If one or more cylinders continue to have abnormally low compression pressures, perform the cylinder combustion pressure leakage test. Refer to DIAGNOSIS AND TESTING .
  12. Install the spark plugs and ignition coils. Refer to SPARK PLUG, REMOVAL AND INSTALLATION .
  13. Install the Fuel Pump Motor fuse to the power distribution center. Refer to FUSE - RELAY LOCATIONS AND TYPES, SPECIFICATIONS .
    NOTE:

    After performing the Cylinder Compression Test, one or more Diagnostic Trouble Codes (DTC's) may have been stored in Powertrain Control Module (PCM) memory due to removal of the ignition coils and the Fuel Pump Motor fuse. A diagnostic scan tool must be used to erase a DTC.

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