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Fuel pump drainback check valve? (16 14 9 068 988)

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    #16
    Originally posted by AndrewBird View Post
    I put mine next to the tank just after the pump, not right at the pump. The short distance from it to the pump isn't enough to cause an issue.
    Next to the tank? By the fuel filter?
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    1991 325i Sport - Calypsorot Metallic - DAILY DRIVEN

    WTB in SoCal: 8"/10" Lukebox, leather Sport steering wheel, 60L MotoMeter fuel gauge, Thule/Yakima roof rack

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      #17
      I would think that no matter your pump setup you'd want the check valve as close to the pick up point for the tank as possible. For me, with an M42, and an in tank single pump it meant putting it less than .75" from the outlet nipple.

      After all, the farther you put it from the feed point (with the bad check valve) the more drain back you will get, the longer your time to pressure at the rail will be on startup, and the longer your initial cranking will be.

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        #18
        If the fuel delivery system is stock and functioning properly, what keeps the fuel from draining back? Is this retrofit being done to avoid replacing an expensive part that functions otherwise (fuel pump, sending unit), but is allowing drain back?

        Thanks, Cory
        1992 325i Cabrio
        1988 320i Touring
        2000 M5
        1977 530i
        2015 328i - Euro Delivery/Performance Center Delivery
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          #19
          A good check valve should work anywhere along the fuel line and it's not a bad idea...but I thought there was one in one or both fuel pumps ?

          Note that check valve says "positive seal at low back pressure or slight vacuum" so it does not matter where you install it
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            #20
            Originally posted by Vincent Brick View Post
            Next to the tank? By the fuel filter?
            Literally on the side of the tank before the filter. There was probably 8" of line from the pump to the check valve.

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              #21
              Originally posted by cory58 View Post
              If the fuel delivery system is stock and functioning properly, what keeps the fuel from draining back? Is this retrofit being done to avoid replacing an expensive part that functions otherwise (fuel pump, sending unit), but is allowing drain back?

              Thanks, Cory
              Pretty sure there is a check valve built into the pump assembly, but that it commonly fails before the pump itself, so these are added to avoid replacing an expensive pump that still mostly works. At least that is what I have gathered, tank side of the fuel system is one of the only things in these cars I haven't messed with much.


              Originally posted by AndrewBird View Post
              Literally on the side of the tank before the filter. There was probably 8" of line from the pump to the check valve.
              I'll have to get underneath and look, about to right now. On my car there is a lot more than 8" of fuel line from the pump to the side of the tank where the fuel filter resides.
              sigpic
              1991 325i Sport - Calypsorot Metallic - DAILY DRIVEN

              WTB in SoCal: 8"/10" Lukebox, leather Sport steering wheel, 60L MotoMeter fuel gauge, Thule/Yakima roof rack

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                #22
                Just following up to add that I finally got the check valve installed yesterday, and it seemed to solve both the revving/stalling issue at cold start and the long warm starts (usually requiring two tries). The only place I could find where this particular valve+fittings would fit easily was immediately after the fuel filter, but it does the job despite what would seem like a less-than-optimal position within the fuel system.

                Thanks again for the help everyone, no more telling people "nah it's ok, it does this."



                UPDATE EDIT:

                The check valve actually did not cure my very cold start (only after sitting overnight) revving/missing/stalling, but did fix the warm start issue. Just wanted to state this for any future troubleshooters reading this.
                Last edited by Vincent Brick; 01-23-2018, 11:17 PM.
                sigpic
                1991 325i Sport - Calypsorot Metallic - DAILY DRIVEN

                WTB in SoCal: 8"/10" Lukebox, leather Sport steering wheel, 60L MotoMeter fuel gauge, Thule/Yakima roof rack

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                  #23
                  I also added a fuel check valve recently, although at first it seemed to solve my long cranking time when I let my car sit for a while it doesn't help anymore and it seems like my fuel pressure regulator is leaking.

                  I was able to put the check valve right after the pump in between the two metal fuel lines.
                  1990 325iX Touring - November 2018 R3V Car Of The Month

                  1980 Volkswagen Golf mk1 1.1
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