1. Relay Itself:
* Failed Relay: The relay may have simply burned out. This is a common and relatively inexpensive fix. Try swapping it with a known good relay of the same amperage and configuration (check the relay's markings).
2. Wiring Issues:
* Blown Fuse: Check the fuse(s) related to the fuel pump circuit in the fuse box (under the hood and possibly inside the car, depending on your specific model). A blown fuse is often the simplest explanation.
* Damaged Wiring: Look for broken, corroded, or chafed wires anywhere along the path from the power source (usually the battery, via the ignition switch) to the relay. This includes the wires leading to and from the relay itself. A visual inspection is crucial, but a multimeter can help confirm continuity.
* Loose Connections: Poor connections at any point in the circuit (fuse, relay, wire harness) can interrupt power flow. Tighten any loose connectors you find.
3. Ignition System Problems:
* Ignition Switch Malfunction: The fuel pump relay is often activated through the ignition system. A faulty ignition switch might not be sending the necessary signal to energize the relay.
* Ignition Control Module (ICM) Issues: The ICM controls various aspects of the ignition, and a malfunction could prevent the relay from receiving the correct signal. This is less likely but possible.
* Inertia Switch: Some vehicles have an inertia switch (a safety device that cuts power to the fuel pump in a collision) that might have tripped. Locate it (often under the dash) and reset it if needed.
4. Other Control Modules:
* Computer (PCM/ECM): In some cases, a problem with the car's Powertrain Control Module (PCM) or Engine Control Module (ECM) can prevent it from sending the signal to activate the fuel pump relay. This is less common but requires a diagnostic scan tool to investigate.
Troubleshooting Steps:
1. Check the fuses. This is the easiest and cheapest first step.
2. Visually inspect the wiring harness and connections. Look for obvious damage.
3. Swap the relay with a known good one. This quickly isolates the relay as a possible cause.
4. Use a multimeter to test for power at the relay's terminals. This will help pinpoint where the circuit is broken. You'll need a wiring diagram to know which terminals should have power under what conditions.
5. Check the inertia switch (if equipped).
If you're not comfortable working with automotive electrical systems, it's best to take your Firebird to a qualified mechanic for diagnosis and repair. Improper handling of electrical components can be dangerous. A wiring diagram specific to your 1991 Pontiac Firebird will be essential for proper troubleshooting. These are often available online or through auto parts stores.
