Description
1. If there is a drop in engine power, or if there is a misfire, and the fault is not related to the ignition or fuel system, a compression test can provide you with information on the probable cause of the fault
2. The engine must be warmed up to operating temperature, the battery must be fully charged, and the spark plugs must be removed. You will also need the help of another person.
3. Turn off the ignition system by disconnecting the low voltage from the ignition coil ("+15"). Install a compression gauge in the spark plug hole of cylinder #1.
4. Lock the throttle in the fully open position, turn the engine over with the starter. Record the highest compression gauge reading.
5. Repeat the test on the remaining cylinders, recording the compression values.
6. The pressure difference between any two cylinders must not exceed 1.0 bar. If any cylinder pressure is low, add engine oil to the spark plug hole and repeat the test.
7. If compression improves temporarily after adding oil (rise), this indicates wear on the cylinder wall or piston ring. If there is no improvement, then the leak is either through burned out valves or a burnt cylinder head gasket.
8. Low compression between two adjacent cylinders is almost certainly due to a blown head gasket between them.
9. At the conclusion of the test, install the spark plugs, connect the low-voltage wire to the ignition coil.
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