Compression Test

Test Description
To diagnose valve or piston faults and poor engine operation, a compression test must be performed to determine the cylinder compression pressure. When checking cylinder compression, the throttle must be wide-open, all three spark plugs removed and the battery at or near full charge. Test each cylinder four times.

Testing Procedures

- Tool Required:
- J 22794 Spark Plug Port Adapter, Or Equivalent

NOTE: Be certain to clean any debris from around spark plug holes prior to removing spark plugs.

1. Turn ignition switch to LOCK.
2. Remove all three spark plugs and disconnect distributor electrical connector. Refer to Ignition System.





3. Remove FI fuse from fuse and relay box.

Compression Gage Installation:

4. Install a J 22794 and a compression gage into a spark plug hole.
5. Disengage the clutch (manual transaxle equipped vehicles) to lighten starting load on the engine and depress the accelerator pedal to the floor (wide-open throttle).
6. Crank engine (with a fully charged battery) to take four pressure readings,

Measure
- The highest pressure reading on the compression gage.
- Standard compression pressure is 1,400 kPa (199 psi) at 250 rpm.
- Minimum allowable compression pressure is 1,100 kPa (156.4 psi) at 250 rpm.

7. Repeat compression test procedures for remaining two cylinders.

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

8. Remove the J 22794 and compression gage from the engine.
9. Install all three spark plugs and connect the distributor electrical connector. Refer to Ignition System.
10. Install FI fuse to fuse and relay box.

Evaluation
- Normal operation-If the cylinder compression pressure increases quickly and evenly to the compression standard (1,400 kPa/199 psi at 250 rpm), the pistons, piston rings and valves are operating normally.
- Piston rings faulty-If the cylinder compression is low on the first stroke and tends to increase on following strokes (but does not reach the compression standard), the probable cause is the piston rings are faulty. The addition of on should improve the compression pressure considerably.
- Valves faulty-If the cylinder compression is low on the first smoke and does not increase on following strokes, the probable cause is that the valves are faulty. Lee addition of oil does not significantly improve the compression pressure.