1. Ignition Switch: This is a very common culprit. The ignition switch provides power to the fuel pump circuit, but only when the key is in the "on" or "start" position. A faulty ignition switch might not be sending power to the fuel pump circuit at all, or only intermittently.
2. Wiring Issues:
* Broken or Corroded Wires: Check the wiring harness leading to the fuse and relay. Look for any signs of damage, breaks, or corrosion, especially at connection points. Pay close attention to the wires near the engine, as they're exposed to heat and vibration.
* Loose Connections: Ensure all connections at the fuse, relay, and any related connectors are secure and making good contact. A simple loose connection can interrupt the circuit.
* Short Circuit: A short circuit elsewhere in the system could blow a fuse or trip a safety mechanism, preventing power from reaching the fuel pump. This requires careful inspection of the wiring harness.
3. Inertia Switch: Some vehicles (though not all) have an inertia switch that cuts power to the fuel pump in the event of a collision. Check your owner's manual to see if your Cutlass Supreme has one and if so, locate it and reset it. It's usually a small button or switch, often located under the dash.
4. Fuel Pump Relay itself: While you mention it, a faulty relay is entirely possible. You can test the relay (check online for how to test a fuel pump relay specifically for your vehicle's year and make) or simply swap it with another relay of the same amperage to see if that resolves the issue (make sure to note which relay you remove and replace in the correct location).
5. PCM (Powertrain Control Module): The PCM controls many aspects of the fuel system. A faulty PCM could prevent power from reaching the fuel pump, though this is less likely than the other problems listed.
6. Fuse (Obvious but important!): Double-check the fuse itself. Even if you think you've checked it, visually inspect it for a blown element. Use a multimeter to verify continuity if you're unsure.
Troubleshooting Steps:
1. Start with the simple stuff: Check the fuse first. Replace it if it's blown.
2. Test the relay: Test the relay or swap it with a known good one.
3. Inspect the wiring: Carefully examine the wiring harness for any damage, breaks, or loose connections from the ignition switch to the fuse and relay.
4. Check the inertia switch (if applicable): Reset the inertia switch if your car has one.
5. Use a multimeter: A multimeter is invaluable for testing voltage and continuity in the circuit. You can check for voltage at the fuse and relay terminals to trace where the power is dropping out.
6. Consult a wiring diagram: Obtain a wiring diagram specific to your 1993 Cutlass Supreme 3.1L. This will help you trace the circuit and identify components.
If you're not comfortable working with car electrical systems, it's best to take your vehicle to a qualified mechanic. Incorrect troubleshooting can lead to further damage.
