Fuel issue? 86 F250 302 windsor

Discussion in '1980 - 1986 Ford F150, F250 and F350 Truck Forum' started by Dkmadd56, Dec 28, 2020.

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  1. Dkmadd56

    I have an 86 F250 with a fuel issue. It has a 302 windsor and my external fuel pump is fine. The truck drives and idles great for about 15 minutes of driving then starts to spit and sputter when throttle is applied. I did a fuel injection test and it idles at about 26-27 psi. I'm wondering if it could be vapor lock or bad in tank fuel pump.
     
    Dkmadd56, Dec 28, 2020
    #1
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  2. FTZ HAIC Staff Member Oregon Chapter Founding Member

    Its probably not vapor lock, that is pretty rare thing with fuel injection. You should be seeing 35-40 PSI fuel pressure when running. You should see it rise by 5 psi or more if you disconnect the vacuum line from the regulator. If not, then it's the regulator (probably). If it's low all the time, it's probably the pump.

    You should be able to hear both the frame rail and in tank pumps when you first key-on. And check the fuel filter too.
     
    FTZ HAIC, Dec 28, 2020
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  3. Dkmadd56

    I'm not sure which vacuum line you are referring to. Mine doesn't have a vacuum line on the valve cover due to a previous owner that removed the oem air filter and replaced it with 2 cone air filters. The air diverter valve is also completely disconnected. If that adds any necessary information. It runs fine idling. But for some reason when throttle is applied and when going uphill, it sputters to the point it almost dies.
     
    Dkmadd56, Dec 28, 2020
    #3

  4. Dkmadd56

    Also when it gets fully warmed up the injection tester loses almost all fuel pressure and it sputters out and dies
     
    Dkmadd56, Dec 28, 2020
    #4

  5. FTZ HAIC Staff Member Oregon Chapter Founding Member

    The pressure regulator should have a vacuum line. Heavier throttle has higher vacuum, and the regulator uses this to increase fuel pressure.

    Vacuum does not come from the valve cover, it's from the intake manifold. If you didn't have a vacuum line from there to a vacuum system the transmission would not shift right, you wouldn't have power braking assist, or spark advance. Part of the system even goes into the cab because there things in there that are vacuum operated, like the heating and ac system.

    If you can hear the two fuel pumps, the pressure regulator is the next thing to check. It looks like this:

    PR15_Front__ra_p.jpg #ad
     
    FTZ HAIC, Dec 28, 2020
    #5

  6. Dkmadd56

    I put new fuel pressure regulator in and it almost seems worse. It sounded great when I fired it up but it started sputtering after about 30 seconds of driving. I also found the vacuum line had been melted apart so I reconnected it to where the other hose looked like it came from. And there is vacuum on the hose coming from the pressure regulator. My fuel pressure is also fluctuating between 20-30psi at idle
     
    Dkmadd56, Jan 7, 2021
    #6
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