Compression Check: Testing and Inspection

Compression Check

1. Start and run engine until normal operating temperatures are reached (thermostat open).
2. Remove all spark plugs.
3. Disconnect both coil negative (WB) leads.
4. Insert compression gauge into spark plug hole and turn engine over until compression stabilizes.
5. Expected readings, throttle fully open, battery fully charged:

^ 11.5 - 12.2 bar (170 - 180 psi).

6. If compression is appreciably less than specification, 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.