Engine Compression Test

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

Perform a compression test in order to determine the cylinder compression pressure. Use a compression test in order to diagnose lack of power, excessive oil consumption, or poor fuel economy.

NOTE: This engine is equipped with an aluminum cylinder head. Allow the engine to cool before removing spark plugs. Removing the spark plugs from an engine at operating temperature may damage the spark plug threads in the cylinder head. Also be sure to clean any dirt or debris from around spark plug holes prior to removing spark plugs.

Important: The engine should be at room temperature.

Verify that the battery is fully charged.
Remove the engine cover (1) from the engine.

Fig 1: Removing Engine Cover
Courtesy of GENERAL MOTORS CORP.
Remove the four ignition coils (1-4) from the cylinder head cover.

Fig 2: Removing Ignition Coils
Courtesy of GENERAL MOTORS CORP.
Remove the spark plugs from the cylinder head.
Remove the EFI Main Relay (2) from the Fuse/Relay Block 1.

Fig 3: Removing EFI Main Relay
Courtesy of GENERAL MOTORS CORP.
Install a compression gage into a spark plug hole.

Fig 4: Installing Compression Gage
Courtesy of GENERAL MOTORS CORP.
Depress the clutch pedal on vehicles that are equipped with a manual transmission.
Depress the accelerator pedal to the floor for a wide open throttle.
Crank the engine through 4 compression strokes for each cylinder being tested.
Important: The maximum allowable compression pressure difference between any 2 cylinders is 100 kPa (15 psi).
Measure the highest pressure reading on the compression gage.
- The standard compression pressure is 1,500 kPa (218 psi).
- The minimum allowable compression pressure is 1,000 kPa (145 psi).
Repeat the compression test procedures for the remaining three cylinders.
Remove the compression gage from the engine.
Install the 4 spark plugs.
Install the 4 ignition coils (1-4) to the cylinder head cover.

Fig 5: Installing Ignition Coils
Courtesy of GENERAL MOTORS CORP.
Install the engine cover (1).

Fig 6: Installing Engine Cover
Courtesy of GENERAL MOTORS CORP.
Reconnect the EFI Main Relay (2) to the Fuse/Relay Block 1.

Fig 7: Connecting EFI Main Relay
Courtesy of GENERAL MOTORS CORP.
Inspect for the following conditions:
- Normal operation
  The pistons, piston rings and valves are operating normally if the cylinder compression pressure increases quickly and evenly to the compression standard (1,500 kPa [218 psi]).
- Faulty piston rings
  The following actions indicate that the piston rings are faulty:
  - The cylinder compression is low on the first stroke.
  - The cylinder compression increases on the following strokes but does not reach the compression standard.
- Faulty valves
  The following actions indicate that the valves are faulty:
  - The cylinder compression is low on the first stroke.
  - The cylinder compression does not increase on the following strokes.