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    FPR question

    I have been troubleshooting a fuel pressure bleed down issue for a while now. The rail doesn't hold pressure after the car is shut down. It slowly bleeds down.

    If I clamp the supply line it still bleeds down so I know it's not the check valve. If I clamp the return line it slows it way down and retains pressure longer.

    Bentley says "repeat the above pressure
    test while gradually clamping off the return hose at the fuel
    pressure regulator as shown in Fig. 6-26. The pressure should
    rise to at least 3.2 bar (46.4 psi) or possible higher. If it does,
    then the pressure regulator is faulty and should be replaced"

    When I clamp down on the return line while jumpering the relay it'll shoot up to like 80psi. Tried 3 different FPRs that I have, all 3 same result so it's hard for me to believe they are all faulty. One was on from PO, one is a used one from a local member, one was a new one from Autohaus AZ that I have been running for months now.

    Could it still be the FPR? I don't think it's injectors leaking but not sure how to know for sure. They were rebuilt and flow tested.
    '90 325is

    #2
    No, that's right- if you block the return, the pressure should rise to whatever the maximum
    your pump can put out. In this case, 80 psi. I dunno what Bentley was smoking.
    I mean, think about it- if you clamp the return while the pump is running,
    where the hell else is the fuel going to go? Maybe it's supposed to say "If it does NOT,"

    But clamping the return line and having it not bleed down DOES point toward
    the regulator having a bit of a 'seep' to it. It also absolves your injectors- if they
    were leaking, clamping the return wouldn't make any difference. I think you might have
    3 leaky regulators.... odd as that might seem.

    t
    now, sometimes I just mess with people. It's more entertaining that way. george graves

    Comment


      #3
      Originally posted by TobyB View Post
      But clamping the return line and having it not bleed down DOES point toward
      the regulator having a bit of a 'seep' to it. It also absolves your injectors- if they
      were leaking, clamping the return wouldn't make any difference. I think you might have
      3 leaky regulators.... odd as that might seem.

      t
      How about 4 bad regulators? I hooked up an adjustable FPR I had laying around and it still bled down, slower but still bled down. I'm wondering if it could be some connection in the fuel rail? Where the FPR mounts maybe? The o-ring looks good and seated and I don't see any fuel leaking in that area.

      I just don't want to spend $120 on a new regulator just to have the same problem.
      '90 325is

      Comment


        #4
        Do you have another set of injectors to swap in?
        AWD > RWD

        Comment


          #5
          I don't. Not stock anyway. Just some yellow top 19 lb'ers

          Sent from my SAMSUNG-SM-G930A using Tapatalk
          '90 325is

          Comment


            #6
            Originally posted by Hoffbrohaus View Post
            How about 4 bad regulators? I hooked up an adjustable FPR I had laying around and it still bled down, slower but still bled down. I'm wondering if it could be some connection in the fuel rail? Where the FPR mounts maybe? The o-ring looks good and seated and I don't see any fuel leaking in that area.

            I just don't want to spend $120 on a new regulator just to have the same problem.
            It's not the regulator. I just installed a known working regulator and my pressure still bleeds down. Any ideas? I really don't think it's a leaky injector since I had them ultrasonically cleaned and tested. But maybe one isn't seated in the rail right?
            '90 325is

            Comment


              #7
              ive not had much issue in the past with pressure leakdown as long as the fuel remained in the lines and rail so it primed back upto pressure really quick.
              89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

              new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

              Comment


                #8
                ignore me, i re-read your post and didnt have anything further to add.

                Comment


                  #9
                  How old are the o rings on the injectors?
                  It's not too hard a project to take off the fuel rail and swap the O rings. When you are testing the fuel pressure, do you have the injector wiring harness disconnected? Don't know if that will make a difference but in theory if there was voltage to an injector for some reason, it may cause a leak-down.

                  Comment


                    #10
                    So if not leaky injectors, how about leaky fuel pump check valve, or old hoses above the fuel tank and in the engine bay?

                    Comment


                      #11
                      Originally posted by uturn View Post
                      So if not leaky injectors, how about leaky fuel pump check valve, or old hoses above the fuel tank and in the engine bay?
                      yeah if youve changed the FPR and still leaks down clamp the hose off again and retest or add another check valve. nothing like having two issues at the same time but not knowing it, then solving one of them and still having the issue....
                      89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                      new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                      Comment


                        #12
                        Thanks guys Ill try it this weekend.
                        1. unplug wiring harness
                        2. vice grip line after FPR
                        3. Check lines above tank under rear seat

                        O-rings were recently replaced, injectors were all done professionally by MEPEH
                        '90 325is

                        Comment

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