Compression Check: Testing and Inspection
Engine Compression Test1. Ensure that the vehicle batteries are in good condition, and fully charged.
2. Operate the vehicle until the engine is at normal operating temperature.
3. Disconnect the positive ignition Coil wire plug from the ignition Coil.
4. Disconnect the fuel injector electrical connector.
5. Remove all of the spark-plugs.
Notice: Do not insert objects into the throttle plate opening. Damage to the throttle body can result, requiring replacement of the throttle body assembly.
6. Block the throttle linkage wide-open.
7. Install the engine cylinder compression gage to the cylinder being tested.
8. Using the vehicle starter motor, rotate, or crank the engine for 4 compression strokes, or puffs, for the cylinder being tested. If the engine rotates for more than 4 compression strokes, test the cylinder again.
9. Record the compression reading.
10. Remove the engine cylinder compression gage from the cylinder being tested.
11. Repeat steps 8-11 for each additional cylinder. All cylinders must be tested to obtain valid test results.
12. Check the compression readings.
^ Normal
The compression builds up quickly and evenly to the specified compression.
^ Leaking
The compression is low on the first compression stroke. The compression builds up with the following strokes, but does not reach the specified compression.
13. If any cylinders have low compression, inject approximately 15 ml (1 oz) of engine oil into the cylinder through the spark plug hole.
14. Repeat steps 8-11 for all low compression cylinders.
15. Check the compression readings.
^ Piston rings leaking
Compression is low on the first compression stroke. The compression builds up on the following strokes, but does not reach normal. Compression improves considerably when you add oil.
^ Valves leaking
Compression is low on the first compression stroke. The compression does not build up on the following strokes, and does not reach normal. Compression does not improve much, if at all, when you add oil.
^ Head gasket leaking
Compression is low on the first stroke. The compression does not build up on the following strokes, and does not reach normal. Compression does not improve much, if at all, when you add oil. Adjacent cylinders have the same, or similar, low compression readings.
16. If one or more cylinders fails to meet the minimum specified compression, repair or replace all damaged or worn components and test the engine again.