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Thread: Need help on fuel pump/pressure diagnosis - new member

  1. #1
    Join Date
    Dec 2011
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    Hebron, IN
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    1997 Z3 Roadster 2.8l

    Need help on fuel pump/pressure diagnosis - new member

    Hello:

    I am new to the forum and have a question about fuel delivery on a 1997 Z3 2.8l 6 cylinder. Short story - I picked this Z3 up very cheap as my nephew ran into a deep water puddle and sucked in some water. Ended up that I pulled the engine and replaced two connecting rods. While doing this, I went throught the entire fuel and engine system,etc - took over two months. I have the engine back in and just got the injectors cleaned professionally. I have Bentley's book on the Z3. Also, fuel pump was replaced (aftermarket) as well as fuel filter and all lines (to and return) were flushed.

    Here is the problem - when I turn the key, the fuel pumps run for about 2 seconds. When I check the fuel pressure - its zero. When the fuel pump runs for the two seconds, fuel will come out of the test port (shoots out actually), but when the pump stops, there is no pressure. From what I read in the Bently book, there should be some 51 pounds after the key is turned and before the engine starts?? If so, what is causing the fuel to run back to the tank? Here are no leaks. I looked at the fuel control valve that has the fuel pressure regulator - all visually looks ok?

    On my GM truck, once the key is turned and left, the fuel pressure remains at 60, on the BMW, there is none.

    I did jumper the fuel relay under the dash and the fuel pump remains running - as it should be.

    Is there supposed to be 50+ pounds of pressure once the system is pressurized? If so, is that such thing as a check valve in the fuel line somewhere? If so, where is it located? I cannot find anything on a check valve for the 1997 Z3.

    I suspect it could be the fuel control valve, but dont know how to test.

    Man, I spent two hours working on this, and all I got was fuel all over.


    Any help could be appreciated.

    Thanks
    Mark

  2. #2
    Join Date
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    E36/7 E36/8x2 E46 F25
    The check valve is built into the pump.

    Does yours have the 3-2 valve? I'm assuming so from your description. When you have this, the fuel pressure regulator is on the block under the drivers feet. The job of this valve is to route how the fuel gets to the pressure regulator. Closed, all fuel goes to the rail, through and back to the block, then regulated and dumped to the tank. With it open, the fuel is regulated straight away, excess dumped, and both lines to the rail are pressurized... dead head. Either way, the regulator has the final say in the pressure.

    The first test I would do is to pinch off the return line to the tank, and trigger the 2 second pump prime. You should pull over 80PSI and it should hold reasonably well.


    /.randy

  3. #3
    Join Date
    Dec 2011
    Location
    Hebron, IN
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    1997 Z3 Roadster 2.8l
    Randy:

    I was wondering if the fuel control valve might have something to do with it. I did take a set of grips and pinched off the return line, turned on the key and after the 2 second fuel pump run, no pressure. Its like when the fuel pump turns off, its like there is no check valve to hold the pressure.

    On the fuel pump, I kept the fuel sending unit from BMW, but used a Highflowfuel performace pump as a direct plug in replacement. I have an email to them regarding the check valve issue.

    Mark

  4. #4
    Join Date
    May 2002
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    99-01 M Cpe & Rdts, X5M
    Overstating the obvious, but are you certain that the supply & return lines weren't mixed up when you put the sending unit back in; or at the filter?

    When I connect a fuel injection cleaner to the fuel rail, I usually see right at 50PSI on my gauge. I set my air pressure (to force the cleaner through the running engine's injectors) at 45PSI to not overcome the fuel pump pressure, which would result in putting my solvent into the tank.

    Edit: visual aids...













    Edit II: it would be easy to reconnect this fuel filter incorrectly, swapping supply/return lines...

    Last edited by Randy Forbes; 12-05-2011 at 09:51 AM.

  5. #5
    Join Date
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    Even with no checkvalve in there, it should hold pressure for a bit, with a slow drainback. If you clipped the return line then had nothing, I suspect Randy may have the right idea. Might want to check flow and direction-of-flow at the filter.

    Tank -> pump -> filter -> 3/2 block <-> engine -> regulator -> return
    Last edited by rf900rkw; 12-05-2011 at 12:23 PM.


    /.randy

  6. #6
    Join Date
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    1997 Z3 Roadster 2.8l
    Guys:

    This bothered me quite a bit, so I drained the fuel out today and pulled the sending unit out. Found that the small hose between the fuel pump and the housing had a small split in it. Replaced it (it was also new too) with a new one, and its holding pressure now.

    Still working out kinks trying to get this running. Found my Idle Speed Control Valve was locked up (it was humming last night) due to sitting for 4 years. Ordered up a replacement today.

  7. #7
    Join Date
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    Quote Originally Posted by markbritt View Post
    Guys:

    This bothered me quite a bit, so I drained the fuel out today and pulled the sending unit out. Found that the small hose between the fuel pump and the housing had a small split in it. Replaced it (it was also new too) with a new one, and its holding pressure now.

    Still working out kinks trying to get this running. Found my Idle Speed Control Valve was locked up (it was humming last night) due to sitting for 4 years. Ordered up a replacement today.
    Parrallel lives: I replaced one of those 2 days ago...







    Glad you're working your way through the problems.

  8. #8
    Join Date
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    The two Randy's hard at work. Good to see guys!
    "Dezmar, your hood has an airfoil. The scoop is raised and it forms an airplanes airfoil. This knocks out the top atoms and allows the bottom atoms to Lift!! You will loose your hood on the highway and hit another car, causing it to crash and someone will Die! (I took it off)"

  9. #9
    Join Date
    Dec 2011
    Location
    Hebron, IN
    Posts
    45
    My Cars
    1997 Z3 Roadster 2.8l
    Randy:

    Would like to chat off line with you about diagnosing some problems with my car, but I cannot PM you directly. Could you contact me at the following address?

    Thanks
    Mark

    markbritt at hotmail dot com

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