- Charge the battery if the battery is not fully charged.
- Disable the ignition system.
- Disable the fuel injection system.
- Remove all spark plugs.
- Turn the ignition to the ON position.
- Depress the accelerator pedal to position the throttle plate wide open.
- Start with the compression gauge at zero and while observing the gauge,
crank the engine through 4 compression strokes. Record the reading and repeat
for the remaining cylinders.
Important: 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 1035 kPa (150 psi), the lowest allowable
pressure for any other cylinder is 725 kPa (105 psi). (1035 x 70% = 725)
(150 x 70% = 105).
- 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.
| • | 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. |
