Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Fuel Supply System
An electric fuel pump (located inside fuel tank as an integral part of the fuel gauge sending unit) supplies fuel under pressure to the throttle body assembly. On most engines, a fuel pump relay controls fuel pump operation. When the ignition is on, the fuel pump relay activates the fuel pump for 2 seconds to prime the injector(s). On some 5.7L and 7.4L engines, a fuel module circuit is installed so that the fuel pump will run for 20 seconds when ignition is turned on.
On all engines, if the ECM does not receive reference pulses (engine cranking) from the distributor after this priming period, the ECM deactivates the fuel pump relay. The fuel pump relay will be activated again when the ECM receives distributor reference pulses.
As a back-up system to the fuel pump relay, the fuel pump can also be activated by oil pressure sending unit. The sending unit has 2 internal circuits. One circuit operates the oil pressure indicator in the instrument panel.
The second circuit is normally an open switch which closes when the oil pressure reaches about 4 psi (.3 kg/cm2 ). If fuel pump relay fails, oil pressure sending unit will close, and supply voltage to fuel pump.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.