1. Fuel Pump Relay: This is the most frequent cause. The relay acts as a switch, turning the pump on and off. A failing relay can cause intermittent power to the pump. Testing and replacing the relay is usually inexpensive and relatively easy.
2. Wiring Issues: Corrosion, damaged insulation, loose connections, or broken wires in the circuit leading to the fuel pump can interrupt power. Inspect the wiring harness, particularly near the tank and connections to the relay and pump. Look for chafing, rodent damage, or corrosion.
3. Inertia Switch: This safety device shuts off the fuel pump in a collision to prevent fire. If it's tripped (usually a small, usually red button under the dash or in the engine bay), it needs to be reset. Check your owner's manual for its location.
4. Fuel Pump Module (In-Tank Pump): The fuel pump itself might be failing. Internal components can wear out or get clogged, leading to inconsistent operation. This often requires replacing the entire fuel pump module, which is a more involved repair. Symptoms might include weaker-than-normal pump sounds during operation as well.
5. Low Fuel Level: While not strictly "intermittent," a very low fuel level can sometimes cause the pump to struggle to draw fuel, leading to sporadic operation.
6. Power Supply Issues: Problems with the battery, alternator, or other components in the vehicle's electrical system can also affect the fuel pump's power supply.
7. PCM (Powertrain Control Module): In rare cases, a faulty PCM can cause intermittent fuel pump issues. This is less likely but should be considered if other components have been checked and ruled out.
Troubleshooting Steps:
1. Check the fuel level: Ensure the tank isn't nearly empty.
2. Listen for the fuel pump: Turn the ignition key to the "on" position (don't start the engine). You should hear a brief whirring sound from the fuel pump area (usually near the rear of the vehicle). If you don't hear it, or it's weak or intermittent, the problem is likely with the pump, relay, or wiring.
3. Check the inertia switch: Locate and reset the inertia switch if present.
4. Inspect the wiring: Carefully examine the wiring harness leading to the fuel pump for any signs of damage.
5. Replace the fuel pump relay: This is a cheap and easy fix, and often solves the problem. A new relay is inexpensive from an auto parts store.
6. Test the fuel pump (advanced): This usually requires specialized tools, but you can test the pump’s voltage and current to confirm its function. This may require professional assistance.
Important Note: Working with fuel systems can be dangerous due to the flammability of gasoline. If you're not comfortable performing these checks yourself, it's best to take your truck to a qualified mechanic.
