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85 mustang fuel pump not primeing

Have done the eec test and fuel pump works and also checked relay and was fine getting 12v from the yellow but when you turn the key on no 12v on pink black wire unless i do the eec test and red is 12v with key on which is from the inertia switch but then the tanish brown one is the problem with the eec test it gets no voltage and without it gets 12v whhich i found out only is suppost to come on when the pump stops pumping as i found out on my 89 f150. when i turn the key on the fuel pump, pumps 0V until it stops itself which is when the tan/brown gets 12V I think there is a relay somewere in the dash that has gone bad. because when i turn it off it stays on for a couple of secs (12v at brown/tan) and then you hear a small click coming from the passenger side dash (0v brown/tan)i already went threw this check list

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  • Jay Whittlesey
    Jay Whittlesey Apr 02, 2014

    the part of the checklist i went through was the no fuel pressure

  • Jay Whittlesey
    Jay Whittlesey Apr 02, 2014

    1985 3.8 v6 lx


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See if the oil pressure switch has 3 prongs. If so and it's leaking oil, that may be the problem. I can't recall what year they stopped doing that switch but my '89 had it. Aside from that, check the fuel pump relay. It can click and still not supply power to the pump.

Posted on Apr 02, 2014

Testimonial: "well i already checked the fuel relay which is under the drivers seat in 1985 lx mustang v6. The click im hearing though is not the problem its just when that happens thats when the pump shuts off or the voltage changes in my f150 which is working correctly but i know its not the relay because I swapped the relay into my truck, in the mustang the fuel pump is not working correctly its like what I was saying above the pump is suppost to prime when you first turn key on and the tan/brown wire is suppost stay off for a couple of seconds (12v black/pink at this time) and then tanish/brown wire gets 12v (0v Black/pink wire at this time)so what ever is triggering that brown or tanish (im not sure of the color on this wire) wire is what makes the black/pink get 12V when its at 0V with the key on. and when that happens the fuel pump comes on beacuse that wire goes all the way to the fuel pump and if i do the eec test it makes the tanish/brown wire 0v and the pump will come on unless the inertia switch has been tripped. Also how would the oil leak cause it to make the fuel pump not to come on, also this all happened when I used the fuel pump test on the eec to ground and pump the old gas out the tank but after i was done the pump will not prime or pump while started unless you use the eec test and you will be able to make the pump run to start but that is the only way it will work now."

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  • James Blair
    James Blair Apr 02, 2014

    Do you know where the inertia switch is? I recently had to bypass the one in my '89 Ford Ranger because it kept quitting on the highway and I wanted to sell it.

  • James Blair
    James Blair Apr 02, 2014

    The oil pressure switch fed ground to the relay to make it engage. If the motor had low oil pressure, it shut off the pump to "save" the motor.

  • Jay Whittlesey
    Jay Whittlesey Apr 02, 2014

    the inertia switch is fine i have already tried bypassing the switch it does nothing. So how do i know oil pressure is the problem the check engine light has not come on at all.

  • Jay Whittlesey
    Jay Whittlesey Apr 02, 2014

    it pump wont work with the eec test if the inertia switch is not working. but it did so that for sure is not the problem or the relay, and the fusible link is good also. the inertia switch is in the back by the trunk hatch in the mustang.

  • James Blair
    James Blair Apr 02, 2014

    So it runs if you bypass with the EEC test?

  • Jay Whittlesey
    Jay Whittlesey Apr 02, 2014

    yes i found out just now that when i start it black stuff comes out the tail pipe and the idle is rough before when i first did the eec test it ran smooth.

  • Jay Whittlesey
    Jay Whittlesey Apr 02, 2014

    the black stuff being on the ground and a big wet spot on the ground from the tail pipe


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