Cylinder Compression Pressure
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Pontiac Grand Prix, 2003 Pontiac Bonneville, 2003 Chevrolet Monte Carlo, 2003 Chevrolet Impala, and 2003 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
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.
- Disable the ignition by removing the Powertrain Control Module (PCM) and the ignition fuses from the appropriate fuse block. See PCM/ICM FUSE LOCATION table.
- Disable the fuel system. Remove fuel pump fuse. See FUEL PUMP FUSE LOCATION table.
- 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:
- Firmly install Compression Tester (J 38722), or equivalent, to the spark plug hole.
- Have an assistant crank the engine through at least 4 compression strokes in the testing cylinder.
- Check and record the readings on the compression tester at each stroke.
- Disconnect the compression tester.
- 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 100 psi (689 kPa).
- 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 3 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 2 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 PCM/ICM fuses removed.
- Install the fuel pump fuse removed.
PCM/ICM FUSE LOCATION
| Model |
PCM |
ICM |
Location |
| Bonneville |
PCM BATT Fuse No. 8 (10-Amp) |
DIS Fuse No. 15 (20-Amp) |
Underhood Fuse Block |
| Grand Prix |
ECM SENSE Fuse No. 33 (10-Amp) |
ELEK IGN Fuse No. 25 (15-Amp) |
Underhood Fuse Block |
| Impala |
PCM Fuse No. 19 (15-Amp) |
ICM DFI MDL Fuse No. 15 (15-Amp) |
Underhood Fuse Block |
| LeSabre |
PCM IGN 1 Fuse No. 19 (10-Amp) |
DIS Fuse No. 14 (20-Amp) |
Underhood Fuse Block |
| Monte Carlo |
PCM Fuse (15-Amp) |
ICM DFI MDL Fuse No. 15 (15-Amp) |
Underhood Fuse Block |
| Park Avenue |
PCM Fuse (10-Amp) |
C31 Fuse (10-Amp) |
Left Underhood Fuse Block |
| Regal |
PCM BCM IGN RELAY Fuse (10-Amp) |
ELEK IGN Fuse No. 26 (15-Amp) |
|
FUEL PUMP FUSE LOCATION
| Model |
Fuse Identification |
Location |
| Bonneville |
F/PMP Fuse No. 1 (20-Amp) |
Rear Fuse Block |
| Grand Prix |
FUEL PUMP Fuse No. 32 (15-Amp) |
Underhood Fuse Block |
| Impala & Monte Carlo |
F/PMP RLY Fuse (15-Amp) |
Underhood Junction Block |
| LeSabre |
F/PMP Fuse No. 1 (20-Amp) |
Rear Fuse Block |
| Park Avenue |
F/PMP Fuse No. 1 (20-Amp) |
Left Underhood Fuse Block |
| Regal |
F/PMP Fuse No. 35 (15-Amp) |
Underhood Fuse Block |