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Thread: FPRs causing power loss?

  1. #1
    Join Date
    May 2011
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    Brunei
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    My Cars
    1990 BMW 850i

    FPRs causing power loss?

    The good:

    -No problems starting,
    -idles fine,
    -Engine not stalling

    The bad:
    -revving up is slow. you can tell that its low on power. forget going up a hill
    -one FPR leaking into vacuum line
    -No CELs on the dash

    Fixes done:
    -Spark plugs replaced (copper), noticed that all the plug tips on the the right bank is pitch black. before installing checked both sides and have strong spark so can rule out Dist, Rotors Coils I think.


    The Problem:
    -Will a faulty FPR cause one bank from not firing optimally? The vacuum line routes to the bank that has the black plug tips. Im thinking too much fuel not burning. New set of fprs are on the way now but just wondering if theres anything to look for? Fuel pump seems ok, have not tested pressure yet though.
    91 BMW 850i LAGUNENGRUEN METALLIC

  2. #2
    Join Date
    Jun 2014
    Location
    So. Cal, USA
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    216
    My Cars
    1995 740iL, 1995 850ciA
    Possibilities,
    A. MAF feeding the black bank giving ECU bad value.
    B. DK on the black bank not opening properly.
    C. Air filter that feeds the black bank clogged with wet cement dust/oatmeal/wet leaves/wet feathers/fine sand...

    Basically the black bank can't breathe.

    Had a Calypso 1991 with clear vacuum lines to FPRs. Used to watch droplets of fuel travel to intakes.
    Car ran fine. Droplets of fuel weren't enough to matter.

    D. Rubber connector on bottom of air filter that feeds black bank collapsed inward into air filter input.
    Last edited by CDO5OO1A; 03-31-2018 at 03:29 AM.

  3. #3
    Join Date
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    11/88 E32 750iL+98 E36M3
    Pull the vacuum hoses from the fuel pressure regulators, if you see drops of fuel coming out, diaphragm of FPR broken.
    SHOGUN'S TRICKS AND TIPS FOR THE SEVEN SERIES
    http://twrite.org/shogunnew/topmenu.html

  4. #4
    Join Date
    May 2011
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    1990 BMW 850i
    Quote Originally Posted by CDO5OO1A View Post
    Possibilities,
    A. MAF feeding the black bank giving ECU bad value.
    B. DK on the black bank not opening properly.
    C. Air filter that feeds the black bank clogged with wet cement dust/oatmeal/wet leaves/wet feathers/fine sand...

    Basically the black bank can't breathe.

    Had a Calypso 1991 with clear vacuum lines to FPRs. Used to watch droplets of fuel travel to intakes.
    Car ran fine. Droplets of fuel weren't enough to matter.

    D. Rubber connector on bottom of air filter that feeds black bank collapsed inward into air filter input.
    I think the MAF should be working as intended, Switching sides does not cause any changes.

    I have inspected only visually but the DK motors seem to be moving as intended when Accelerator pedal is pressed. No dirt or gunk or whatnot internally that will impact its operation either.

    Air Filter has been cleaned and inspected.

    I have not checked rubber connectors, will do so. Thank you.

    Quote Originally Posted by shogun View Post
    Pull the vacuum hoses from the fuel pressure regulators, if you see drops of fuel coming out, diaphragm of FPR broken.
    Hi Shogun, yes the FPR is leaking as I mentioned. Not just drops but pouring out quite a bit at the vacuum hose end of the FPR. The question is would a leaky FPR cause an entire banks worth of plugs go black and impede performance? I am worried that there are other issues that might be causing the loss in power.

    FPRs are on the way and will be replaced as a set.
    91 BMW 850i LAGUNENGRUEN METALLIC

  5. #5
    Join Date
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    11/88 E32 750iL+98 E36M3
    Yes. a broken FPR can cause this trouble. Normally it let's thru just enough fuel needed and at 3 bar, if the FPR is broken, more volume is fed by the 2 fuel pumps and the fuel pumps usually have a higher pressure than 3 bar, so more volume and more pressure = the fuel injector opening time is controlled by the Motronic based on 3 bar, if the pressure is higher, more volume goes thru the injectors within the same injector opening time.
    The Top 7 of Bad Symptoms https://cartreatments.com/fuel-pressure-regulator-info/
    SHOGUN'S TRICKS AND TIPS FOR THE SEVEN SERIES
    http://twrite.org/shogunnew/topmenu.html

  6. #6
    Join Date
    Jun 2014
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    1995 740iL, 1995 850ciA

    Shugun gets right to the point, I check the possibilities ....

    Quote Originally Posted by Fiiz View Post
    I think the MAF should be working as intended, Switching sides does not cause any changes.

    I have inspected only visually but the DK motors seem to be moving as intended when Accelerator pedal is pressed. No dirt or gunk or whatnot internally that will impact its operation either.

    Air Filter has been cleaned and inspected.

    I have not checked rubber connectors, will do so. Thank you.



    Hi Shogun, yes the FPR is leaking as I mentioned. Not just drops but pouring out quite a bit ...
    ... other issues that might be causing the loss in power.

    FPRs are on the way and will be replaced as a set.

    Ok so,
    Not MAF,
    Not DK's,
    Not Air filters.
    You have greatly reduced the possibilities.

    If it is the case that the FPRs are allowing full fuel pump pressure at the injectors
    then this is the other side of the coin, too much fuel instead of not enough air.

    Replace 1 FPR on black bank then continue. If this clears the problem then go ahead and replace second FPR as a preventative measure.

  7. #7
    Join Date
    May 2011
    Location
    Brunei
    Posts
    49
    My Cars
    1990 BMW 850i
    Just an update;

    FPRs were replaced and no noticeable difference.

    But we found the problem! One of the internal hoses in the fuel pump assembly 'looked' as if it is snugly fitted but just popped out of its fitting when fiddling with it. Replaced all the internal rubber hoses (2nd pump hose looked ok but since already out might as well change it all) and power is back on!

    Thinking of doing a single pump method and putting a connector. I think shogun did this in one of his threads?

    Many thanks for the input here guys.
    91 BMW 850i LAGUNENGRUEN METALLIC

  8. #8
    Join Date
    Aug 2007
    Location
    Canada
    Posts
    199
    My Cars
    745Li, 850i, LR3 HSE
    Fuel pump, also replace fuel filters.

    Mark.


    Quote Originally Posted by Fiiz View Post
    The good:

    -No problems starting,
    -idles fine,
    -Engine not stalling

    The bad:
    -revving up is slow. you can tell that its low on power. forget going up a hill
    -one FPR leaking into vacuum line
    -No CELs on the dash

    Fixes done:
    -Spark plugs replaced (copper), noticed that all the plug tips on the the right bank is pitch black. before installing checked both sides and have strong spark so can rule out Dist, Rotors Coils I think.


    The Problem:
    -Will a faulty FPR cause one bank from not firing optimally? The vacuum line routes to the bank that has the black plug tips. Im thinking too much fuel not burning. New set of fprs are on the way now but just wondering if theres anything to look for? Fuel pump seems ok, have not tested pressure yet though.
    Last edited by mandd; 04-14-2018 at 08:57 AM.

  9. #9
    Join Date
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    6.5 second 69 Camaro
    Thanks for the update!

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