inconssitant fuel pressure

Discussion in '4.0 Engine' started by buckfever, May 14, 2012.

  1. buckfever

    buckfever New Member

    I am having trouble with my fuel pressure and I am not sure which I have. I do not know if the FPR is on the rail or in the tank. I had a buddy change my fuel pump when I was away on vacation and he didn't remember seeing the regulator in there with the pump. So I am going to post a picture and see if anyone could tell me if it is a regulator or a damper in the photo. Thanks in advance. 98 Ranger 4.0 4x4 auto
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  3. rwenzing

    rwenzing Bob

    98 and later Ranger has the fuel pressure regulator inside the fuel tank on the pump assembly. The part on the 98+ rail is the fuel pulse damper.
  4. OP

    buckfever New Member

    Does the damper cause the fuel pressure to go up and down?
  5. rwenzing

    rwenzing Bob

    Your 98 pressure should be a constant pressure of about 64 PSI +/- 8 PSI. The damper does not affect overall system pressure but helps to minimize pressure waves within the rail.
  6. ZRanger28

    ZRanger28 Got boost?

    could it be the fuel filter is clogged causing funny fuel psi readings?
  7. OP

    buckfever New Member

    No I put a new fuel filter in it. I think I will just take out the pump and change the regulator and see if that fixes it. I don't have a problem driving unless I stay at a constant speed then I can feel it sputter, but if I get all over it she will still up and go. I also will stop at a red light or something and it will sputter and will do so until I can get going usually by third gear it will stop.
  8. rwenzing

    rwenzing Bob

    Have you actually measured it during the problem or are you assuming that the fuel pressure is the cause?
  9. OP

    buckfever New Member

    Actually measured went from 50 psi down to 25 psi.
  10. OP

    buckfever New Member

    The weird thing is it runs better with about two gallons left then if I have a full tank it doesn't run good at all?????
  11. OP

    buckfever New Member

    Anyone else have ideas?
  12. rwenzing

    rwenzing Bob

    To summarize:

    New fuel pump.
    New fuel filter.
    Measured fuel pressure drops to 25 PSI during the problem.
    Swapped regulator?? You didn't report back on that one.

    I'd also pull a vacuum on the pulse damper and see if it holds - it should if the diaphragm is OK

    If all of the mechanicals seem OK, I'd look at electrical next.

    For starters, I'd monitor voltage across the pump when the pressure drops to see if it is following a drop in voltage. Possible electrical problem areas could be the Fuel Pump Relay, the Fuel Inertia Switch, the pump ground or a poor connection in any connector in the fuel pump circuitry. The pump ground is bolted to the radiator core support near the battery. The relay is in the underhood Distribution Box. The Inertia Switch is in the passenger footwell.
    Last edited: May 20, 2012

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