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: 2.2L
- Start engine and bring coolant temperature to 176°F (80°C). Remove sensing resistor, glow plug connector and fuel cut solenoid connector. Disconnect fusible link wire of glow plug system. Remove all glow plugs.
- Install adapter (J-26999-20) and compression gauge. Turn starter motor and read compression for individual cylinders.
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.