- Charge the battery if the battery is not fully charged.
- Remove the coil pack from each cylinder head.
- Remove all of the spark plugs.
- Disable the ignition system, fuel injection, and open the throttle
plates wide open, using a Tech 2 under the Compression Test screen.
- Start with the compression gage at zero.
- Turn the key to start position and release. The engine will automatically
crank.
- Make a compression check for each cylinder. Record the reading.
- If a cylinder has low compression, inject approximately 15 ml,
(1 tbsp) of engine oil into the combustion chamber through the spark
plug hole. Recheck the compression and record the reading.
- The minimum compression in any one 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 one cylinder were 1035 kPa (150 psi) the lowest allowable
pressure for any other cylinder would be 725 kPa (105 psi).
1035 x 70 percent, 150 x 70 percent = 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 then 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 two 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. |
