1993 Pontiac Trans Sport 3.8L - Code P042 Issue: Intermittent Engine Death & Diagnosis Steps

My 1993 Pontiac Trans Sport with a 3.8L engine is experiencing intermittent stalling—after running for a mile or two, the vehicle suddenly dies and restarts only to stall again shortly after. The Engine Control Module (ECM) consistently reports Diagnostic Trouble Code (DTC) P042, which corresponds to an Electronic Spark Timing (EST) Circuit fault. I have already replaced the Ignition Control Module (ICM), crankshaft position sensor, camshaft position sensor, and the ECM itself. I've also installed new spark plugs and ignition wires with no improvement. The issue persists. The DTC P042 is known to be related to an EST circuit problem—often stemming from wiring faults such as open circuits, shorted connections, or faulty components in the ignition system. Based on the trouble tree, I need to systematically test the EST and bypass circuits to isolate whether the issue lies in wiring, the ignition module, or the ECM itself. Steps for diagnosis: 1. Clear any existing codes and idle the engine for about one minute until DTC P042 appears. If it does not set, the problem may be intermittent. 2. Turn off the ignition, then disconnect the ECM connectors. 3. Turn the ignition back on and use an ohmmeter (set to 1000–2000 Ω range) to test resistance between the EST circuit in the ECM harness and ground—the reading should be under 1000 Ω. 4. If resistance is high, inspect for loose connections, open circuits, or a faulty ignition module. 5. If the circuit checks out, use a test light connected to battery voltage to probe the bypass circuit. 6. If the test light illuminates, disconnect the distributor's 4-way connector and observe: - If the light goes off → faulty ignition module - If it stays on → bypass circuit is shorted to ground 7. If the test light remains off, retest the bypass circuit with both the test light and ohmmeter: as the test light touches the bypass circuit, resistance should rise from under 1000 Ω to over 2000 Ω. - If it does → reconnect ECM and idle; if DTC P042 returns, the ECM is faulty - If not → intermittent issue 8. If resistance doesn’t increase when the distributor connector is disconnected → EST circuit is shorted to ground 9. If all tests pass but stalling continues → bypass circuit may be open or have a faulty connection. Note: After resolving the issue, clear codes and verify closed-loop operation with no 'Service Engine Soon' warning light. I am currently at a loss—any additional guidance on locating the EST and bypass circuits would be greatly appreciated.