Mechanical Inspection: Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions. Release fuel system pressure before checking engine compression. See FUEL SYSTEM .

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 the ignition switch during cranking mode, which can cause a fire hazard, or contaminate the engine's oiling system.

COMPRESSION SPECIFICATIONS

Application

Specification

Compression Ratio

4.0L

9.5:1

6.0L

11.0:1

Compression Pressure ⁽¹⁾

4.0L

160-170 psi (11.2-12.0 kg/cm² )

6.0L

200-240 psi (14.1-16.9 kg/cm² )

Maximum Variation Between Cylinders

10 psi (.70 kg/cm² )

⁽¹⁾	Minimum cranking speed is 300 RPM with all spark plugs removed and throttle held wide open.