Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1985 GMC Forward Control 6.2 J, StandardFACTORY OEM SERVICE PROCEDURE
Engine Compression: 6.2L
- Remove air cleaner. Disconnect electrical wire from fuel injection pump solenoid terminal.
- Disconnect glow plug wiring, and remove all glow plugs. Use compression gauge (J-26999-10) to test individual cylinders.
COMPRESSION SPECIFICATIONS
| Application | Specification | ||||
|---|---|---|---|---|---|
| Compression Ratio | |||||
| 2.2L | 21.0:1 | ||||
| 6.2L | 21.3:1 | ||||
| Compression Pressure | |||||
| 2.2L | |||||
| Standard | 441 psi (31 kg/cm2 ) (1) | ||||
| Minimum | 398 psi (28 kg/cm2 ) (1) | ||||
| 6.2L | 300 psi (21 kg/cm2 ) | ||||
| Max Pressure Variation - 6.2L | 20% | ||||
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Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.