Mechanical Inspection: Compression
WARNING:
DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system.
Ensure battery is fully charged and starter motor is in good operating condition. Clean spark plug recesses with compressed air and remove spark plugs. Lock throttle in Wide Open Throttle (WOT) position and Remove Auto Shutdown (ASD) relay. Install compression gauge. Using a remote starter switch, rotate engine 3 revolutions. Record compression pressure from third revolution. Continue test for remaining cylinders. See COMPRESSION SPECIFICATIONS table for correct engine compression pressures. A 50-70 percent reduction in compression between adjacent cylinders indicates a head gasket leak.
COMPRESSION SPECIFICATIONS
| Application | Specification | |||
|---|---|---|---|---|
| Compression Ratio | ||||
| 2.5L | 9.1:1 | |||
| 4.0L | 8.8:1 | |||
| 4.7L | 9.0:1 | |||
| Compression Pressure | (1) | |||
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