Mechanical Inspection: Compression
Check engine mechanical condition with a compression gauge, vacuum gauge or engine analyzer. See engine analyzer manual for specific instructions.
WARNING:
DO NOT
use ignition switch during compression tests on fuel injected vehicles. Crank engine with a remote starter. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system.
COMPRESSION SPECIFICATIONS
| Application | Specification | |
|---|---|---|
| 4.0L | 8.7:1 | |
| 5.2L | 9.1:1 | |
| Compression Pressure | ||
| Normal | 120-150 psi (827-1034 kPa) | |
| Minimum | 100 psi (689 kPa) | |
| Maximum Variation Between Cylinders | 30 psi (207 kPa) | |