- Charge the battery if the battery is not fully charged.
- Disable the ignition system.
- Disable the fuel injection system.
- Remove all the spark plugs.
- Turn the ignition to the ON position.
- Depress the accelerator pedal to position the throttle plate wide open.
- Start with the compression gage at zero and crank the engine through 4 compression strokes, 4 puffs.
- Measure the compression for each cylinder. Record the readings.
- If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole. Measure the compression again and record the reading.
- The minimum compression in any 1 cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any 1 cylinder is
1 035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1 035 x 70% = 725) (150 x 70% = 105).
| • | Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder. |
| • | Piston Rings Leaking -- Compression is low on the first stroke. Compression builds up with the following strokes, but does not reach normal. Compression improves considerably when you add oil. |
| • | Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil. |
| • | If 2 adjacent cylinders have lower than normal compression, and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders. |
