Intermittent "Check Engine" Light Or Stored Codes

Most intermittent problems are caused by faulty electrical connectors or wiring. Diagnosis must include a careful visual and physical inspection of the indicated circuit wiring and connectors. Check the following:

• Check for poor mating of the connector halves or terminals not fully seated in connector body.
• Check for improperly formed or damaged terminals. All connector terminals in the affected circuit should be re-formed to increase contact tension.
• Check that all HEI distributor EST wires are routed away from distributor, ignition coil, secondary wires and alternator.
• Check circuit No. 419 ("CHECK ENGINE" light circuit) for a short to ground.
• Check circuit No. 451 (diagnostic connector to ECM) for a short to ground.
• Check circuits No. 450 and 450R for an ECM ground at engine block attachment.
• Check for electrical interference caused by a defective relay, ECM driven solenoid, or a switch causing a sharp electrical surge. The problem will occur when the defective component is operated.
• Check for improper installation of electrical options.
• Check for open A/C clutch diode.

1. 2) If the complaint is stalling, rough or improper idle speed, see Chart 11, Fig. 27.
2. 3) If the engine cranks, but will not run, see Chart 4 or 4A, Fig. 7 or 8.
3. 4) If the complaint is hard starting, poor performance, driveability or poor fuel economy, see CHART 7, POOR PERFORMANCE (NO STORED CODES) in this article.
4. 5) If the complaint is detonation (spark knock), see Chart 10 ESC Performance (if applicable), Fig. 26, or chart 8, Fig. 17.
5. 6) If driver complains of poor performance with A/C on, problem is with the A/C system. Refer to appropriate article in the AIR CONDITIONING section.

Following any repairs or adjustments, always clear codes and confirm closed loop operation and "CHECK ENGINE" light.