1. Fuel System:
* Fuel Pump: A weak or failing fuel pump won't deliver enough fuel to the engine. Listen for the pump's whirring sound when you turn the key to the "on" position (before cranking). If you don't hear it, or hear a weak whirring, the pump may be failing. Testing fuel pressure with a gauge is crucial.
* Fuel Filter: A clogged fuel filter restricts fuel flow. Replacing it is relatively inexpensive and easy.
* Fuel Injectors: Clogged or failing injectors can prevent proper fuel delivery. This often requires professional diagnosis and cleaning or replacement.
* Fuel Pressure Regulator: A faulty regulator can cause incorrect fuel pressure. This needs to be tested with a gauge.
2. Ignition System:
* Distributor Cap and Rotor: Cracked or worn components in the distributor can interrupt the spark. Inspect for cracks, corrosion, or worn contacts. Replace if necessary.
* Spark Plugs and Wires: Worn or fouled spark plugs and damaged wires prevent a strong spark. Check for gaps and corrosion. Replace as needed.
* Ignition Coil: A faulty coil won't generate the high voltage needed for sparking. This needs testing with an ohmmeter.
* Ignition Module (Electronic Ignition Control Module - EICM): This controls the ignition timing and can fail, causing stalling. Diagnosis often requires specialized tools.
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational position. A faulty CKP will prevent the engine from starting or running smoothly.
3. Air Intake System:
* Air Filter: A severely clogged air filter restricts airflow, leading to poor engine performance and stalling. Replace it regularly.
* Mass Airflow Sensor (MAF): Measures the amount of air entering the engine. A dirty or faulty MAF sensor provides inaccurate data to the computer, resulting in improper fuel delivery and stalling. Cleaning the MAF sensor (carefully!) can sometimes help.
4. Other Potential Causes:
* Throttle Position Sensor (TPS): Tells the computer the throttle position. A faulty TPS can cause erratic idle and stalling.
* Idle Air Control Valve (IAC): Controls the engine's idle speed. A malfunctioning IAC can cause stalling, especially at idle.
* Vacuum Leaks: Leaks in vacuum lines can disrupt the engine's operation. Inspect all vacuum hoses for cracks or damage.
* Computer Problems (PCM): The Powertrain Control Module can malfunction and cause numerous issues, including stalling. This is often the hardest to diagnose and may require professional help.
* Alternator: A failing alternator can cause the battery voltage to drop, leading to stalling. Test the alternator's output voltage.
* Battery and Cables: A weak battery or corroded battery cables can also prevent starting and cause stalling.
Troubleshooting Steps:
1. Start with the easy and inexpensive checks: Air filter, battery terminals, spark plugs and wires.
2. Listen for unusual sounds: Whining from the fuel pump, clicking from the ignition system, etc.
3. Check engine codes: If the Check Engine light is on, use an OBD-I scanner (appropriate for a 1991 vehicle) to retrieve diagnostic trouble codes (DTCs). This will provide clues about the problem.
4. Visual Inspection: Look for obvious problems like broken wires, loose connections, or leaks.
5. Systematic Testing: Work your way through the potential problems listed above, testing each component as needed. You may need a multimeter and a fuel pressure gauge.
Important Considerations:
* Safety First: Always disconnect the battery's negative terminal before working on the electrical system.
* Professional Help: If you're not comfortable working on your car's electrical or fuel systems, take it to a qualified mechanic. Some of these repairs require specialized tools and knowledge.
This information is for guidance only. The actual cause of your Caprice's stalling problem may require further diagnosis by a qualified technician. Remember to always consult your vehicle's repair manual for specific procedures and specifications.
