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Short Summary
Main recommendation: Before replacing a fuel pump, test for simpler causes such as a blown fuel pump fuse, an tripped inertia switch, or a faulty fuel pump relay, then confirm with a fuel pressure gauge; if the pump is getting power but produces no fuel pressure, replace the pump (and the fuel filter) as the host did on his 1998 Mustang GT. The video is a step-by-step diagnosis and replacement walkthrough that applies, according to the host, to most cars with an in-tank fuel pump.
Key Points
- Turn the key to Run and listen for the pump to prime for about two to three seconds; silence does not automatically mean the pump has failed.
- Check the fuse first, then confirm about 12 volts reaches the fuel pump harness at the rear of the car.
- Test the inertia switch in the trunk, which cuts fuel pump power after an impact and can trip from a pothole or heavy object.
- Swap the fuel pump relay (located in the passenger-side footwell on this Mustang) if it does not click when the key is turned to Run; the host notes they are inexpensive.
- Use a fuel pressure gauge at the fuel rail: a pump that receives power but shows zero pressure points to the pump itself rather than a clogged filter, which would cause slow or partial pressure rise.
Details Worth Noting
- Concrete instructions:
- Turn the key to Run, listen for the prime, and confirm the sound; if none, proceed with checks.
- Remove the fuse listed as "fuel pump" in the owner's manual fuse diagram (under the hood, behind the battery on this Mustang), inspect it, and measure with a multimeter across both sides of the holder; expect about 12 volts.
- At the rear harness by the tank, disconnect the pump connector, ground the black lead to bare metal (the host used the exhaust), turn the key to Run, and probe each prong with the red lead; expect about 12 volts on each.
- Press the red button on the inertia switch in the trunk; if it pops up, press it back down until it clicks to reset.
- Remove the Schrader valve cap at the fuel rail and attach a gauge; with the key on, pressure should rise to at least about 30 PSI and hold.
- Before dropping the tank, remove as much fuel as possible, disconnect the filler neck screws, disconnect the battery's negative terminal, and have a fire extinguisher nearby.
- Replace the fuel filter at the same time as the pump so the new pump runs efficiently.
- To prime after installation, cycle the key to Run and off three times to pressurize fuel and fill the lines, then start the engine.
- Check for fuel leaks at the quick-disconnect fittings after the repair, especially when refueling.
- The host dropped the tank with a jack and used a special tool to release the quick-disconnect fuel lines; he tightened the tank strap bolts to 38 ft-lb while pressing upward as he screwed them in.
- Access to the pump may be possible through the trunk or rear seats in some cars, so check before dropping the tank.
- The host replaced only the pump inside the fuel pump assembly, noting you could instead replace the entire assembly, but chose to replace just the pump since it was the only bad part.
Bottom Line
Systematic electrical and pressure testing can separate a simple fuse, switch, or relay fault from a genuinely dead fuel pump, which the host confirmed in this case.
