Dual Fuel Tanks - Problem

Discussion in 'General Discussions' started by Black Pearl, Jul 15, 2011.

  1. Jul 15, 2011 at 1:15 AM #1
    Black Pearl

    Black Pearl Full Access Member

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    1995 F-150 5.8

    I have dual fuel tanks on the truck I just picked up. Runs great off the front tank. The aft tank will run at idle and even if you step on the gas while in park, runs pretty smooth, however..... When I am drive, and when any pressure at all is placed on the gas pedal (while in AFT) it starts running rough and the check engine light comes on. (but not everytime)

    Looking for tips

    Also looking for a diagram of both the fuel line routing and electrical routing for the system. The electrical seems to work, it does switch between tanks, think I might have a clog somewhere. Previous owner changed the fuel pumps in the fuel cells, still didn't fix it, they didn't look any further.

    I can get to all the plumbing under the truck, just need to make sure that what I'm seeing is correct

    Picked up a Hayes book, helps, but doesn't answer all the questions

    Thanks in advance

    Jeff
     
    Last edited: Jul 15, 2011
  2. Jul 15, 2011 at 1:31 AM #2
    The Batman

    The Batman Rest In Piece

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    there is another smaller pump on the frame rail...check that...after that check for clogging in the aft tank or lines...after that we'll get into more detail...simplicity first...that is often the most adept solution the problems at hand....
     
  3. Jul 15, 2011 at 8:45 AM #3
    cowboy

    cowboy Sheriff

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    is there a separate fuel filter for the back one?
     
  4. Jul 15, 2011 at 8:49 AM #4
    iowaredneck

    iowaredneck Administrator

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    ^x2
     
  5. Jul 16, 2011 at 4:17 AM #5
    ksingltn

    ksingltn Full Access Member

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    The frame mounted booster pump was only used from 84 to 90. 91-96's use a single in tank pump per tank.

    Sounds like you may have a faulty fuel pump in the back tank, though that being swapped out somewhat eliminates that option. (Though I have seen new ones go bad fast)

    The "valve" that selects tanks is nothing but a flap that changes the flow based on which pump is energized, so that may be sticking. I have never taken one off or apart, but you may be able to clean it. Does the problem occur at all fuel levels?

    If you are still having issues, I would do a fuel pressure check, rent a gauge from autozone or oreilly's if you don't have one, and hook it up to the small schraeder valve on the fuel rail. (It looks just like a tire valve stem) I can't remember off the top of my head, but I think the fuel pressure is supposed to be 35psi at idle and 40-55 under throttle (Don't quote me, if you need it I can find the actual figures)

    There is only one filter, and it is between the selector "valve" and the engine, so probably not the culprit since it works on the front tank.

    Lol, I guess I jumped right into the more detail
     
    Last edited: Jul 16, 2011

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