Compression Check: Testing and Inspection

Compression Check

1. Start and run engine until normal engine operating temperature is achieved (thermostat open).
2. Remove all spark plugs.
3. Disconnect both coil negative leads
4. Insert compression gauge, crank engine until reading stabilizes.
5. Expected readings, throttle fully open, battery fully charged:

8.31:1 = 10.2-10.9 bar (148-158 psi)
9.35:1 = 11.5-12.2 bar (166.75-176.9 psi)

6. If compression is appreciably less than correct figure, or varies by more than 10%, piston rings or valves may be faulty.
7. Low pressure in adjoining cylinders may indicate a faulty head gasket.