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.
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HOMESERVICE MANUALSCHEVROLET1985FORWARD CONTROL 6.2 J, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCEIGNITION SYSTEMIGNITION SYSTEM - HEI (FEDERAL)TESTING - ESCDETONATION PROBLEMS
1985 Chevrolet Forward Control 6.2 J, Standard
Detonation Problems
1985 Chevrolet Forward Control 6.2 J, StandardSECTION Detonation Problems
NOTE:
Before diagnosis, check connection at sensor and ensure that all connections are clean and tight. Occasional detonation is acceptable.
- Adjust engine to about 1000 RPM. With transmission in Neutral or Park, lightly tap exhaust manifold repeatedly. Check for timing retard with a timing light. If retard is noted, detonation sensor is functional.
- If no retard occurs, backprobe 10-pin connector at ESC controller located in passenger compartment. Connect voltmeter leads between pins "B" and "K" of connector. With engine operating at 2000 RPM, voltage should read 80 millivolts (.08). If voltage is correct, go to step 5).
- If meter reading was incorrect, disconnect detonation sensor wire. Measure resistance from sensor terminal to ground. Reading should be about 99 ohms. If ohmmeter reading is incorrect, replace sensor. If okay, repair wiring circuit from pin "B" to sensor.
- If ohmmeter reading in step 2) was okay, try to start engine with 4-pin connector disconnected. If it starts, stop engine and attach high resistance test lamp from "TACH" terminal to ground. If lamp lights, and flickers during engine cranking, system is okay. If lamp does not light/flicker, replace ignition module or pole piece.
- If engine will not start, reconnect 4-pin connector. Disconnect sensor wire from sensor, and insert a jumper wire into sensor wire connector. With engine running at fast idle speed, lay wire on top of distributor over ignition coil. If spark timing retard occurs, replace sensor.
- If no spark retard occurs, connect voltmeter positive lead to pin "H" of 10-pin connector and negative lead to pin "K". With ignition switch on, voltage should read more than 0.2 volt. If voltage is over 0.2 volt, replace ESC controller. If less than 0.2 volt, repair open wire from pin "H" in ESC harness.
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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.