1. Fuel Pump Relay: This is the most common culprit. The relay acts as a switch, sending power to the fuel pump.
* Check the relay: Locate the fuel pump relay (consult your owner's manual or a wiring diagram). Visually inspect it for damage. A simple test is to swap it with another relay of the same amperage rating (a different, similar relay in the fuse box, *never* swap a random relay unless you're sure). If the problem moves, the relay is faulty.
* Listen for clicking: When you turn the ignition key to the "ON" position (not cranking), you should hear a brief click from the relay. No click usually indicates a bad relay or a problem in the relay circuit.
2. Fuel Pump Inertia Switch: This safety device cuts power to the fuel pump in a collision to prevent fire.
* Locate and check: Find the inertia switch (often under the dash or in the engine compartment—consult your owner's manual). It usually has a button that you can push to reset it. If it's tripped, pushing the button should restore power.
3. Wiring and Connections: A break, short, or corroded connection in the wiring between the relay, inertia switch, and fuel pump can interrupt power.
* Visual inspection: Carefully examine all wiring related to the fuel pump for damage, chafing, or corrosion. Pay close attention to connectors.
* Continuity test: Using a multimeter, check for continuity (a complete electrical circuit) in the wiring. This requires some electrical knowledge.
4. Fuel Pump Fuse: Though less common, a blown fuse can cut power. Check the fuse box for a fuse related to the fuel pump.
5. Computer/ECU Issues: In some cases, a problem with the car's computer (Powertrain Control Module or PCM) could prevent it from sending the signal to activate the fuel pump relay. This is less likely but possible. A diagnostic scan tool is needed to check for computer codes.
6. Fuel Pump itself: The fuel pump could be faulty. Testing it directly (checking voltage at the pump with a multimeter when the key is on) or listening for the pump's hum when the ignition is switched on will help determine if it is the culprit. This often requires dropping the fuel tank, which is a more involved job.
Troubleshooting Steps:
1. Start with the easiest: Check the fuel pump relay and the inertia switch first.
2. Visual inspection: Thoroughly inspect all wiring and connections.
3. Use a multimeter: Check for continuity in the wiring and voltage at the fuel pump.
4. Consult a wiring diagram: A wiring diagram specific to your 1990 Ford Mustang 2.3L is essential for accurate troubleshooting.
5. Consider professional help: If you're not comfortable working with car electrical systems, it's best to take your car to a mechanic.
Remember safety first! Disconnect the negative battery terminal before working on any electrical components. Gasoline is flammable, so take precautions when working near the fuel tank.
