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Home >> GMC >> 1983 >> Forward Control 7.4 W, Standard >> Repair and Diagnosis >> Engine Performance >> Ignition System - HEI >> Testing >> Electronic Spark Control (ESC) Testing >> Detonation Problems
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Detonation Problems

NOTE: Before diagnosis, check connection at sensor and ensure that all connections are clean and tight. Occasional detonation is acceptable.
  1. 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.
  2. If no retard occurs, disconnect 10-pin connector from ESC controller, located in passenger compartment. Connect ohmmeter leads between pins "B" and "K" of connector. Ohmmeter should read about 99 ohms. If so, proceed to step 5).
  3. 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.
  4. 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.
  5. 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.
  6. 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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