Engine Compression
Check engine compression pressure with engine at normal operating temperature and all spark plugs removed. Ensure throttle plates are wide open and battery is fully charged.
On fuel injected engines, remove fuel pump or ECM fuse. On engines equipped with Direct Ignition System (DIS), disconnect battery connector from coil. On engines equipped with Integrated Direct Ignition (IDI) system, remove cover and 11-pin IDI harness connector. On all other engines, disconnect battery terminal from HEI distributor.
The lowest cylinder reading should not be less than 70 percent of the highest cylinder reading. No cylinder reading should be less than 100 psi (7 kg/cm2 .
COMPRESSION SPECIFICATIONS
| Application | Compression Ratio |
|---|---|
| 4.5L (VIN 3) | 9.5:1 |
| 5.0L (VIN E & F) | 9.3:1 |
| 5.0L (VIN Y) | 8.0:1 |
| 5.7L (VIN 7 & 8) | 9.3:1 |
| Min. Compression Pressure | 100 psi (7 kg/cm2 |
| Max. Variation Between Cylinders | Less than 30% |