Seven Wiki Available

Please check out our wiki available at:
See more
See less

Fuel flow issue

  • Filter
  • Time
  • Show
Clear All
new posts

  • Fuel flow issue

    At the dyno day, it was noticed that I had a fuel flow issue at higher rpm. At the gas station the other day, I had a different fuel flow issue where it was trickling out underneath the car. It seems that the short, large diameter hose between the fuel filler-up-a-lyzer and the fuel tank has developed a "vent" - a crack along the seam. The rubber feels kind of old too, if that makes sense. Anyway, I will obviously be replacing the hose a.s.a.p., but was wondering if any here might know if this could have been the cause of the original issue: fuel pressure dropping off at mid- to high-rpm?
    | | Sean

  • #2

    Am I correct that your fuel pump is inside the tank?

    If the leak is in the filler neck I don't see how it would effect the pressure to the engine.

    These hoses shouldn't be failing so soon. Mines 10 years old and never an issue. I just might check it now.



    • #3
      Yes, I couldn't see how it could be related, but it sure did seem like a coincidence. I have replaced it this evening, and went ahead and re-did the vent per the grads race series as found here.

      Next time I am somewhere I feel noise will not be an issue, and I have somebody with me, I'll rev it up and see if the fuel pressure drop is still there. I may have to see about making a Gert-style mega-muffler so I can rev as needed at home in the future.
      | | Sean


      • #4
        I put a fuel pressure gauge on my regulator that you could see while driving the car.

        Or if your computer does datalogging put in a fuel pressure transducer and record the pressure.

        It needs to be under load to give it a good test.

        Just reving the engine while parked won't do it.



        • #5
          The two things *may* be a bad way. If the filler hose has rotted and shed little bits of black crud into your tank, those bits may have partially blocked your fuel delivery system somewhere (hopefully in a filter, not just in the line itself) so that you get enough flow at lower demand but not enough for WOT.


          • #6
            Good point.

            Change the filter or clean it if you have the cleanable type.

            If a throw away, cut it open and check for blockage.


            • #7
              I don't think that rubber would clog the pump or the filter since there is a a sock on the pickup in the tank that will take care of any debris large-scale debris.

              During the dyno runs Sean's pressure dropped to 35psi (down from 55 or so) at the top end. I compensated for this with longer injector duty cycles, but at that pressure fuel atomization does take a fairly major hit.

              The stock in-tank pump usually poops out trying to feed engines above 200HP; I had to replace mine when I supercharged my old Zetec to around 210HP. (There's a thread somewhere with pics describing the plumping I did).

              I still think a pump upgrade is the right thing to do, which does not have to be expensive, although a remap will be needed since there will be way too much fuel at the top end with a beefed up pump.

              /Magnus F.


              • #8
                The car was spec'd from the beginning to have the uprated fuel pump from the R500, which should be adequate. It is possible that what was spec'd and what was supplied are different - anybody know how to tell externally?
                | | Sean


                • #9
                  I've never inspected an upgraded pump, thus cannot tell if its presence can be determined from the outside.

                  The upgraded one:

                  The standard one:

                  They look more or less identical, which is a surprise. The sock I mentioned earlier is clearly visible in these pictures.

                  If you have an upgraded pump (which I doubt), you probably have a clogged filter. Easily replaced.

                  /Magnus F.