Compression Check: Testing and Inspection

TOOL REQUIRED
^ J 38722 Compression Tester

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. Turn the engine OFF.
3. Disable the ignition system. See Powertrain Management.
4. Disable the fuel system. See Powertrain Management.

CAUTION: Remove the Powertrain Control Module (PCM) and ignition fuse from the I/P fuse block.

5. Remove the spark plugs from all cylinders. See Powertrain Management.
6. Remove the air duct from the throttle body. See Powertrain Management.
7. Block the throttle plate in open position.
8. Measure the engine compression using the following procedure:
a. Install the Compression Tester firmly to the spark plug hole.
b. Have an assistant crank the engine through, at least four compression strokes, in the testing cylinder.
c. Check and record the readings on the gauge at each stroke.
d. Disconnect the gauge.
e. 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% of the highest reading.
^ No cylinder reading should be less than 965 kPa (140 psi).
10. The following are examples of measurement problems:
^ When the compression measurement is normal, the compression builds up quickly and evenly to the specified compression on each cylinder.
^ When low compression is caused by piston rings, compression is low on the first stroke and it does not tend to build up in following strokes, but does not reach normal. Compression does not improve much with the addition of oil. Use approximately three squirts from a plunger type oiler.
^ When low compression is caused by the valves, the measurement is low on the first stroke and does not build up even with the addition of oil.
^ Leaking head gaskets give nearly the same results as valve problems, but may be identified by engine coolant in the crankcase. Head gasket leakage between two cylinders will give low readings on both cylinders.
11. Remove the block from the throttle plate.
12. Install the air duct to the throttle body. See Powertrain Management.
13. Install the spark plugs. See Powertrain Management.
14. Install the PCM.
15. Install the ignition fuse to the I/P fuse block.