Here's a systematic troubleshooting approach:
1. Reconnect the BCM:
* Carefully plug the BCM back in. Make sure the connector is fully seated. A loose connection is a common cause of intermittent electrical problems.
* Try to start the car. If it starts, you were lucky – a simple loose connection was the culprit.
2. Check for BCM Faults (If it still doesn't start):
* Visual Inspection: Examine the BCM connector for any bent pins, corrosion, or damage. Repair or replace as needed. Look for any signs of water intrusion or damage to the BCM itself.
* Scan for Codes: You'll need an OBD-I code reader (specifically for a 1992 Buick) to check for any diagnostic trouble codes (DTCs) stored in the car's computer. These codes can pinpoint the problem.
* Consider BCM Replacement: If you find physical damage to the BCM or persistent codes pointing to it, replacement is likely necessary. This is a more advanced repair and may require professional help.
3. Check Ignition System Components (Beyond BCM Influence):
Even if the BCM is the initial culprit, other components could have been affected by the interruption or have pre-existing problems.
* Ignition Coil: Test the ignition coil for proper resistance using a multimeter. A bad coil won't produce spark.
* Ignition Module (or Control Module): In some GM vehicles of this era, there's a separate ignition module. Its function is closely tied to the BCM and might need testing or replacement. Consult a wiring diagram to locate it.
* Crankshaft Position Sensor (CKP Sensor): This sensor tells the computer the engine's rotational position, essential for timing the spark. A faulty CKP sensor will prevent spark. Test it with a multimeter, again referring to a wiring diagram or repair manual for proper testing procedure.
* Camshaft Position Sensor (CMP Sensor): Similar to the CKP sensor, a faulty CMP can prevent spark.
* Distributor (if equipped): If your Riviera has a distributor, check the cap, rotor, and ignition wires for cracks, burns, or corrosion. Replace any faulty parts.
* Ignition Switch: A faulty ignition switch may not properly supply power to the ignition system.
4. Wiring Harness:
* Inspect Wiring: Look for any frayed, broken, or damaged wires in the ignition system harness, especially around the BCM connector. Repair or replace any damaged wiring.
Important Notes:
* Wiring Diagram: A factory wiring diagram is crucial for this type of troubleshooting. It'll show you the path of the ignition system's electrical flow and help you locate components. These are available online or through repair manuals.
* Safety: Disconnect the negative battery cable before working on any electrical components to avoid injury.
* Professional Help: If you're not comfortable working with automotive electrical systems, it's best to take your car to a qualified mechanic. Improper troubleshooting can lead to further damage.
The no-spark condition after unplugging the BCM strongly suggests a problem related to the BCM itself or its interaction with other ignition system components. Thorough and systematic testing is essential to pinpoint the exact cause.
