Tools Required

J 39313 Spark Plug Port Adapter.

A compression pressure test of the engine cylinders determines the condition of the rings, the valves and the head gasket.

1. Run the engine until it reaches normal operating temperature. The battery must be at or near full charge.
2. Charge the battery if the battery is not fully charged.
3. Turn the engine to the OFF position.




Important: Remove the ignition relay (1) from the under hood body electrical centre (2).

4. Disable the ignition system.




Important: Pull the instrument panel fuse block cover (1) rearward to disengage it from the left hand hinge pillar trim (2).

5. Remove the instrument panel fuse block cover (1).




Important: Remove the fuel pump relay (1) from the instrument panel fuse block (2).

6. Disable the fuel injection system.
7. Remove the spark plugs from all cylinders. Refer to Spark Plug Replacement .
8. Measure the engine compression, using the following procedure:

8.1.	Thread the J 39313 into the spark plug hole.

8.2.	Thread the compression gauge onto the J 39313 .

8.3.	Have an assistant depress the accelerator to the wide open throttle position and crank the engine through, at least 4 compression strokes, in the testing cylinder.

8.4.	Check and record the readings on the gauge at each stroke.

8.5.	Remove the compression gauge from the J 39313 .

8.6.	Remove the J 39313 from the spark plug hole.

8.7.	Repeat the compression test for each cylinder.

9. Record the compression readings from all of the cylinders.

•	The lowest reading should not be less than 70 percent of the highest reading.

•	No cylinder reading should be less than 965 kPa (140 psi).

10. If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole. Measure the compression again and record the reading.

•	Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder.

•	Piston Rings Leaking -- Compression is low on the first stroke. Compression builds up with the following strokes, but does not reach normal. Compression improves considerably when you add oil.

•	Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.

•	If 2 adjacent cylinders have lower than normal compression, and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.





Important: Install the fuel pump fuse to the rear fuse and relay centre fuse block.

11. Enable the fuel injection system.




Important: Push the fuse block access cover (1) forward to engage it to the left hand hinge pillar trim (2).

12. Install the left hand hinge pillar trim fuse block access cover (1).




Important: Install the ignition relay (1) to the under bonnet fuse block (2).

13. Enable the ignition system.
14. Install the spark plugs to all cylinders. Refer to Spark Plug Replacement .