* Fuel System Problems:
* Clogged Fuel Filter: Restricts fuel flow to the engine.
* Fuel Pump Failure: Unable to deliver sufficient fuel pressure.
* Bad Fuel Injectors: Clogged or failing injectors prevent proper fuel delivery.
* Fuel Pressure Regulator Issues: Incorrect fuel pressure in the system.
* Low Fuel Level: Seems obvious, but sometimes overlooked!
* Ignition System Problems:
* Distributor Cap and Rotor Wear: Leads to poor spark distribution.
* Spark Plugs and Wires: Worn or damaged spark plugs and wires can prevent proper ignition.
* Ignition Coil Failure: Doesn't generate sufficient spark voltage.
* Crankshaft Position Sensor (CKP) Problems: The engine computer relies on this sensor to time the ignition. A faulty sensor can cause misfires and stalling.
* Vacuum Leaks: A leak in the vacuum system can disrupt the operation of various engine components, including the brakes and fuel system.
* Throttle Position Sensor (TPS) Issues: The TPS tells the computer the throttle position. A faulty sensor can cause incorrect fuel delivery.
* Mass Airflow Sensor (MAF) Problems: Measures the amount of air entering the engine. A dirty or faulty MAF can lead to a lean fuel mixture and stalling.
* Computer Issues (ECM): Though less common, a faulty engine control module (ECM) can cause a variety of problems, including stalling.
* Transmission Issues (Automatic): Problems within the transmission itself can cause the engine to stall, especially during shifting.
* Alternator Problems: While not directly causing a stall, a failing alternator can lead to low voltage, causing erratic operation and eventual stalling.
Troubleshooting Steps:
1. Check the obvious: Fuel level, and listen for unusual sounds from the fuel pump.
2. Check the basics: Inspect the spark plugs and wires for damage.
3. Get a diagnostic code read: An OBD-I scanner (appropriate for a 1991 Caprice) can help identify trouble codes that point to specific problems.
4. Visual inspection: Look for visible damage, loose connections, or vacuum leaks.
Without more specific information about the circumstances of the stalling (when it happens, any warning signs, etc.), it's impossible to pinpoint the exact cause. Taking it to a mechanic experienced with older vehicles is highly recommended for proper diagnosis and repair.
