Compression Check: Testing and Inspection

In order to diagnose poor engine operation, perform a compression test. A compression test will help determine valve, piston, or piston ring failure. If checking the cylinder compression, the following conditions must apply:
^ The throttle must be wide-open.
^ All of the spark plugs must be removed.
^ The battery must be at full charge or near full charge.
Test each cylinder four times.

^ Tool Required
- J 22794 Spark Plug Port Adapter





1. Turn the ignition switch to LOCK.

Important: Clean any debris from around the spark plug holes prior to removal of the spark plugs.

2. Remove all of the spark plugs, and disconnect the distributor electrical connector. Refer to Spark Plug Replacement in Powertrain Management.
3. Remove the F1 fuse (1) from the fuse and relay box.





4. Install a J 22794 and a compression gauge into a spark plug hole (1).
5. Disengage the clutch in order to lighten the starting load on the engine. Depress the accelerator pedal to the wide-open throttle position.
6. With the battery in the completely charged state, crank the engine through four cycles, in order to take four pressure readings.
7. Measure the highest pressure reading on the compression gauge.
^ Standard compression pressure is 1400 kPa (199 psi) at 250 RPM.
^ Minimum allowable compression pressure is 1100 kPa (156 psi) at 250 RPM.

Important: The maximum allowable difference in compression pressure between any two cylinders is 100 kPa (14.2 psi) at 250 RPM.

8. Repeat the compression test procedures for the remaining cylinders.
9. Remove the J 22794 and the compression gauge from the engine.
10. Install all three spark plugs, and connect the distributor electrical connector. Refer to Spark Plug Replacement in Powertrain Management.





11. Install the FI fuse (1) to the fuse and relay box (2).
12. Evaluate the compression tests:
^ During normal operation, cylinder pressure increases quickly and evenly to the compression standard of 1400 kPa (199 psi) at 250 RPM. The pistons, piston rings, and the valves are operating correctly.
^ The piston rings are faulty if the cylinder compression is low on the first stroke and tends to increase on the following strokes. The compression does not attain the standard. The addition of oil should improve the compression pressure considerably.
^ The valves are faulty if the cylinder compression is low on the first stroke and does not increase on following strokes. The addition of oil does not significantly improve the compression pressure.