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. On 2.5L, disconnect ignition coil connector. On 4.0L, remove coil rail assembly to access spark plugs. On all models, clean spark plug recesses with compressed air. Remove spark plugs. Remove fuel pump relay from power distribution center. See Fig 1, Fig 2 or Fig 3 . Install compression gauge. Hold throttle in Wide Open Throttle (WOT) position. 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.
COMPRESSION SPECIFICATIONS
| Application | psi (kg/cm2 ) | |||
|---|---|---|---|---|
| Normal Compression Pressure | ||||
| 2.5L & 4.0L | 120-150 (8.3-10.5) | |||
| 4.7L | 140-180 (9.8-12.7) | |||
| Maximum Variation Between Cylinders | ||||
| 2.5L & 4.0L | 30 (2.1) | |||
| 4.7L | (1) | |||
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