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.
1987 GMC Forward Control 6.2 J, StandardFACTORY OEM SERVICE PROCEDURE
Engine Compression
NOTE:
Do not add oil to cylinders during compression check as extensive engine damage will result.
Remove air cleaner. Disconnect 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 | 21.3:1 |
| Compression Pressure | 300 psi (21 kg/cm2 ) |
| Max. Pressure Variation | 20% |
Factory Service Tools
Use the Manual With the Right Hardware
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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.