Engine Compression Test
Engine Compression Test |
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Charge the battery if the battery is not fully charged.
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2. |
Disable the ignition system.
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3. |
Disable the fuel injection system.
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4. |
Remove all spark plugs.
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5. |
Turn the ignition to the ON position.
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6. |
Depress the accelerator pedal to position the throttle plate wide open.
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7. |
Start with the compression gauge at zero and crank the engine through 4 compression strokes, 4 puffs.
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8. |
Measure the compression for each cylinder. Record the readings.
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9. |
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.
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10. |
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).
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Normal - Compression builds up quickly and evenly to the specified compression for each cylinder.
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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.
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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.
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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.
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