Tools Required
J 39313
Spark Plug Port
Adapter
A compression pressure test of the engine cylinders determines the condition
of the rings, the valves and the head gasket.
- Run the engine until it reaches normal operating temperature.
The battery must be at or near full charge.
- Turn the engine OFF.
Important: Remove the Powertrain Control Module (PCM) and the ignition fuse from
the IP fuse block.
- Disable the ignition.
- Disable the fuel systems.
- Remove the spark plugs from all cylinders.
- Remove the air duct from the throttle body.
- Block the throttle plate in open position.
- Measure the engine compression, using the following procedure:
8.1. | Thread the
J 39313
into the spark plug hole. |
8.2. | Thread the compression gage into the
J 39313
. |
8.3. | Have an assistant crank the engine through, at least four compression
strokes, in the testing cylinder. |
8.4. | Check and record the readings on the gage at each stroke. |
8.5. | Remove the compression gage from the
J 39313
. |
8.6. | Remove the
J 39313
from the spark plug hole. |
8.7. | Repeat the compression test for each cylinder. |
- Record the compression readings from all of the cylinders.
• | The lowest reading should not be less than 70 percent of
the highest reading. |
• | No cylinder reading should be less than 965 kPa (140 psi). |
- The following are examples of measurement problems:
• | When the compression measurement is normal, the compression builds
up quickly and evenly to specified compression on each cylinder |
• | When low compression is caused by the piston rings, compression
is low on the first stroke and tends to build up on the following strokes,
but does not reach normal. Compression improves considerably with the addition
of oil. Use approximately three squirts of oil from a plunger-type
oiler. |
• | When low compression is caused by the valves, the measurement
is low on the first stroke and does not build up even with the addition of
oil. |
• | Leaking head gaskets will provide the same results as worn valves
but engine coolant may be identified in the crankcase. In addition, a leaking
head gasket will give low readings on paired cylinders. |
- Remove the block from the throttle plate.
- Install the air duct to the throttle body.
- Install the spark plugs.
- Install the Powertrain Control Module (PCM).
- Install the ignition fuses to the IP fuse block.