Fuel System:
* Fuel pump failure: The most common culprit. The pump may have died completely, or it might be intermittently failing. Listen carefully for the whine of the fuel pump when you turn the key to the "on" position (before cranking). No whine suggests a failed pump.
* Fuel filter clog: A clogged fuel filter restricts fuel flow, leading to engine stalling.
* Fuel pressure regulator issues: A malfunctioning regulator can cause incorrect fuel pressure, preventing proper combustion.
* Clogged fuel injectors: Dirty injectors can prevent adequate fuel delivery.
* Low fuel: Sounds obvious, but worth checking!
Ignition System:
* Crankshaft position sensor (CKP) failure: This sensor tells the ECU the crankshaft's position, essential for ignition timing. A faulty CKP prevents the engine from firing.
* Cam position sensor (CMP) failure: Similar to the CKP, a bad CMP prevents proper ignition timing.
* Ignition coil failure: A weak or failed ignition coil won't produce the high voltage needed for spark plugs to ignite the fuel-air mixture.
* Distributor cap and rotor problems (if applicable): While less likely on a 1991 model with electronic ignition, worn components could still be an issue.
* Wiring issues: Corroded or damaged wiring in the ignition system can interrupt the spark.
Other Possibilities:
* Battery: A weak battery might crank the engine but not provide enough power to start it. Test the battery voltage.
* Alternator: While less likely to cause an immediate shutdown, a failing alternator could have already drained the battery to the point of no-start.
* ECU (Engine Control Unit) issues: A problem with the ECU itself, though less common, is possible. This usually requires a professional diagnosis.
* Immobilizer system (if equipped): An anti-theft system could be preventing the car from starting.
* Neutral safety switch: Prevents starting unless the transmission is in Park or Neutral.
* Security system: Some aftermarket security systems can be problematic.
Troubleshooting Steps:
1. Check the obvious: Fuel level, battery voltage, and all fuses.
2. Listen for the fuel pump: Turn the key to "on" (but don't crank) and listen for the fuel pump whine.
3. Check for error codes: Many 1991 models have diagnostic ports that can provide error codes.
4. Check spark: Test the spark plugs to see if they're getting spark. (Caution: high voltage!)
5. Have it professionally diagnosed: If you're not comfortable troubleshooting automotive systems, take it to a mechanic specializing in older vehicles or Japanese cars. They have the tools and expertise to diagnose the problem accurately.
The age of the vehicle makes many of these issues more probable. The twin-turbocharged nature of the VR4 adds another layer of complexity. Start with the simpler checks (fuel, battery, fuses) and proceed from there, but professional help may be necessary.
