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    Fuel Pressure Questions

    1990 325i Sedan (M20)

    Generally when cold starting my idle is rough and around 550 rpm

    When I blip the throttle the car rpm drops and the engine sputters before gaining rpm

    Overall lack of power

    old compression test results here: https://www.r3vlimited.com/board/sho...d.php?t=399036

    I have replaced the fuel filter and the lines before and after the filter with R9 hose (was leaking fuel, the lines were dry rot)

    I replaced the fuel line to the fuel pressure regulator and the vacuum line to the fuel pressure regulator

    I installed an inline T to a gauge on the fuel line below the fuel pressure regulator. Setup as seen in this pic:https://drive.google.com/file/d/0B34...ew?usp=sharing using this gauge: http://a.co/6PNywuD

    At idle (idling around 900) the gauge read ~38 psi stable

    When the throttle was blipped the gauge would shoot up to 50+ and with rpm gain the pressure would drop back to ~38 in seconds (hard to see while inside vehicle)

    When pinching the vacuum line to the fuel pressure regulator the pressure was a stable 45 psi, when released it returned to 38

    After the car was turned off, the pressure remained at 38 for 15+ minutes.

    The car was filled with 89 octane fuel and was approximately 75% full during the test

    Have I properly tested my fuel pressure and FPR? What do these results indicate if they have been taken correctly? If they were not taken correctly, or I have missed something please let me know.
    Last edited by Blobsters; 07-24-2017, 10:05 PM.

    #2
    Best practice is to confirm 100% that you do not have any intake leaks. A smoke test is the best way to accomplish that.
    Seat Shocks....I have passed the baton to John Christy from Ninestitch. Email John or Garrett at ninestitch1@gmail.com

    https://www.r3vlimited.com/board/sho...86#post4944786
    Alice the Time Capsule
    http://www.r3vlimited.com/board/showthread.php?t=360504
    87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

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      #3
      Fuel pressure at idle should be about 38psi. At higher engine speeds it should be about 43psi. Tie wrap the gauge to a windshield wiper and see what happens as you drive.
      The car makes it possible, but the driver makes it happen.
      Jim Levie, Huntsville, AL

      Comment


        #4
        My suspect would be clogging injectors or old cracking injector O rings. You didn't state mileage and injector condition.
        Any fuel in the vacuum line to the FPR?

        Comment


          #5
          Originally posted by ahlem View Post
          My suspect would be clogging injectors or old cracking injector O rings. You didn't state mileage and injector condition.
          Any fuel in the vacuum line to the FPR?
          230k+ miles , no fuel in vacuum line to FPR, unknown condition of injectors. Will pull injectors and flow test/ clean / replace clips/seals.

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            #6
            Have you checked the fuel return?

            [IMG]https://cimg4.ibsrv.net/gimg/my350z.com-vbulletin/550x225/80-parkerbsig_5096690e71d912ec1addc4a84e99c374685fc03 8.jpg[/IMG

            Comment


              #7
              sub'd - I'm suspect of mine as well. If I find anything with mine ill report back here, similar situation except for lack of power.

              Comment


                #8
                my caused ended up being the injectors, i have a stroker motor with a few bolt ons and such, so your cause is probably different then mine.

                I was using the ford injectors, maybe one or two were bad, and when I swapped in my oe injectors it was fine.

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