Compression Check: Testing and Inspection

1. Start and run engine until it reaches operating temperature.
2. Turn ignition switch off.
3. Release fuel pressure as outlined under Technician Safety Information.
4. Disconnect ignition coil with power transistor harness connectors, then remove ignition coils.
5. Remove all spark plugs.
6. Disconnect all injector harness connectors.
7. Attach a compression tester to cylinder No.1.
8. Depress accelerator pedal fully to keep throttle valve wide open.
9. Crank engine and record highest gauge indication.
10. Repeat measurement on each cylinder.
11. At 300 RPM, standard compression is 185 psi and minimum pressure is 142 psi, maximum difference between cylinders is 14 psi.
12. If compression in one or more cylinders is low, pour a small amount of engine oil into cylinders through spark plug holes, then retest compression.
13. If adding oil helps compression, then piston rings may be at fault. If adding oil does not help compression, then valves may be at fault.
14. If compression stays low in two cylinders that are next to each other, then cylinder head gasket may be leaking or both cylinders have valve component damage.
15. Repair as necessary.