Tools Required
J 38722 Compression Tester
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 fuses from
the Underhood fuse block. Refer to
Electrical Center Identification Views
in Body and
Accessories.
- Disable the ignition.
- Disable the fuel systems.
- Remove the spark plugs from all the cylinders.
- Remove the air duct from the throttle body.
- Block the throttle plate in the open position.
- Measure the engine compression, using
the following procedure:
| 8.1. | Firmly install J 38722
to
the spark plug hole. |
| 8.2. | Have an assistant crank the engine through at least four compression
strokes in the testing cylinder. |
| 8.3. | Check and record the readings on J 38722
at each stroke. |
| 8.5. | 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 689 kPa (100 psi). |
- The following are examples of the possible measurements:
| • | When the compression measurement is normal, the compression builds
up quickly and evenly to the specified compression on each cylinder. |
| • | When the compression is low on the first stroke and tends to build
up on the following strokes, but does not reach the normal compression, or
if the compression improves considerably with the addition of three squirts
of oil, the piston rings may be the cause. |
| • | When the compression is low on the first stroke and does not build
up in the following strokes, or the addition of oil does not affect the compression,
the valves may be the cause. |
| • | When the compression is low on two adjacent cylinders, or coolant
is present in the crankcase, the head gasket may be the cause. |
- 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) fuse.
- Install the ignition fuse to the Underhood fuse block.
