fuel pump not turning on

Discussion in 'Fox 5.0 Mustang Tech' started by Mustang Ricky, Dec 11, 2003.

  1. ok, fuel pump is not priming so i got stranded. luckly i found a ride. the fuel pump itself was replace last spring and i did not have any issue with it since then. i figure i first need to confirm that the pump is getting power.

    if it's getting power, then it must be the fuel pump itself.

    if it's not getting power, then i guess is could be the fuel pump relay? could it be something else? if it's the relay, should i replace with the stock part or are the ones from Autozone, Pep Boys, ect a good replacement too?
  2. Try resetting the inertia switch. Its in the trunk, mine is on the drivers side in front of the tail light. Push the reset button and try it. Then make sure power is coming in and out of it. Then I would check out the relay. Some are under the drivers seat and some are under the MAF tube in the engine comp. I would check for power at the pump last, cause its the hardest thing to check. It could even be and ignition switch prob, jiggle it. Just gotta do some searching, you have the right idea, good luck.
  3. Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. http://www.mustangworks.com/article...c-iv_codes.html for a description of the test connector. If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure – remove the cap from the schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

    No fuel pressure, possible failed items in order of their probability:
    A.) Tripped inertia switch – press reset button on the inertia switch. The coupe & hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
    B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter.
    C.) Clogged fuel filter
    D.) Failed fuel pump
    E.) Blown fuse link in wiring harness.
    F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect for fuel escaping while pump is running.

    The electrical circuit for the fuel pump has two paths, a control path and a power path.

    The control path consists of the inertia switch, the computer, and the fuel pump relay coil. It turns the fuel pump relay on or off under computer control. The switched power (red wire) from the ECC relay goes to the inertia switch (red wire) then from the inertia switch to the relay coil and then from the relay coil to the computer (green wire). The computer provides the ground path to complete the circuit. This ground causes the relay coil to energize and close the contacts for the power path. Keep in mind that you can have voltage to all the right places, but the computer must provide a ground. If there is no ground, the relay will not close the power contacts.

    The power path picks up from a fuse link near the starter relay. Fuse links are like fuses, except they are pieces of wire and are made right into the wiring harness. The feed wire from the fuse link (orange/ light brown wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the contacts to the fuel pump (light pink/black wire). The fuel pump has a black wire that supplies the ground to complete the circuit.

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)



  4. well, the fuel pump stopped working on Thurs afternoon, stranding me at a parking lot. I go back up there on Sat to figure out where the problem is and wouldn't you know, the fuel pump turned on and the Stang started.

    I'm not sure if I should be relieved. Finding what went wrong is impossible and I'm now just waiting for the car to strand me again somewhere.