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Thread: Fuel pump getting no voltage

  1. #1
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    Fuel pump getting no voltage

    I've got a 97 540 that is having issues. I can't seem to get the fuel pump to turn on. The car cranks and makes spark but no fuel. I checked the pump with a 12v source and it hums but doesn't produce any fuel pressure. The fuel pump harness is also not providing a 12v signal when the key is at position 2 OR when i crank. I have already checked the fuses in the glove box and the trunk.

    I am getting error code 108 Permanent supply when I scan it with INPA. I had an EWS wiring fault error as well but I had my EWS module repaired by an electronics repair shop. They changed several capacitors and I no longer have that fault. The car cranks and I get spark at the ignition coils but no voltage at the fuel pump.


    I'm suspecting it might be an ews fault? Could the ews cause a no fuel problem? What should I test next?

    Thanks

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    Last edited by ltpickles; 11-20-2017 at 06:08 PM.
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  2. #2
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    From the info you gave it sounds like a bad pump. Humming w/o pressure would likely have blow the fuel pump fuse(you didn't mention checking fuse-I'd start with that), hence no voltage.

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  3. #3
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    the fuel pump itself might be bad but i am also not getting a 12v signal at the fuel pump connector. The fuel pump connector has 4 pins, 2 for the fuel level sender and 2 for the fuel pump's 12v and GND. I am getting 0 volts even when the key is in position 2 or when I am cranking the car. Any ideas?
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  4. #4
    JimLev's Avatar
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    Sounds like the fuel pump is bad. If the pump runs when you applied 12 volts and you had no pressure are you sure the fuel filter isn't clogged?
    With the key in position 2 you'll only have 12 volts at the connector for 2 second. When you crank the engine you should have 12 volts for as long as it's cranking and obviously with the engine running.
    There are 2 fuses that go to the fuel pump relay, have you checked them?

  5. #5
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    I've checked both fuses and they are not fused. I can manually activate the fuel pump relay through inpa so it's working properly. The fuel pump connector does not provide 12v at position 2 even for 2 seconds. It also doesn't provide 12v at cranking. I have a new fuel pump on the way, I'm just trying to figure out the lack of 12v at the connector.

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  6. #6
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    I haven't traced out all of the circuits on the ignition switch, maybe a bad contact in it?????
    The DME controls the fuel pump relay and you are able to turn the pump on with INPA so the wiring from the DME to the fuel pump is good.
    Maybe try syncing the EWS again???

  7. #7
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    I hadn't thought of the ignition switch. I will try that tomorrow and post back

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  8. #8
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    I once had an odd problem where the fuel pump fuse appeared intact, but was actually cracked.

    The symptom was the same as a blown fuse, but when the fuel pump connector was removed to check the voltage it read +12V. I finally figured it out by applying power from a jump start box, which resulted in fuel pressure.

  9. #9
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    they are not fused What do you mean?


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  10. #10
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    They aren't burnt- same as not fused

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  11. #11
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    Did you measure them with an ohmmeter?

    A voltmeter will measure 12 V across the fuse if it's blown (we Old-timers use this term).
    Last edited by edjack; 11-21-2017 at 10:43 PM.


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  12. #12
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    Quote Originally Posted by ltpickles View Post
    They aren't burnt- same as not fused

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    Never heard that one before either, even from our customers in Montreal, Ottawa, Bromount, etc.
    Its either good or blown.

    Have you got the fuel pressure problem figured out yet? Clogged filter?

  13. #13
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    Fuel filter is brand new so don't think that's causing a problem. Never had a fuel pressure issue before , this car sat for a while and now it's doing this.

    The "fused" terminology is used in Asian English. The Brits also like to say it

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    Ill test the fuses with a multimeter to make sure they're not blown.

    Jim hows should I test the ignition switch? Should I Just check for 12v switched when in position 2?
    Last edited by ltpickles; 11-22-2017 at 10:39 AM.
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  14. #14
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    Never had to work on an ign saw problem. There are (IIRC) 9 sets of contacts in it. Good luck.

  15. #15
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    I would expect a fuel filter to clog enough so there's no pressure (plus you'd have drivablity issues long be fore it got clogged) unless the car had sat for a long time and the last fill up was with gasahol. If there was ethanol in the tank there's a good chance there's clogs. Are you sure there's actually enough gas in the tank? I'm assuming the gage indicates some level but I've seen gages be off for various reason and if the car was sitting with a low tank and a loose or missing gas cap the level could be too low.

    The fact that you can energize the pump with INPA tells me fuse is probably fine. I only say probably because one time when I was trouble shooting an electrical problem on a customer's machine a fuse tested good but ended up being the issue.



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  16. #16
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    In my case the cracked fuse showed continuity when measured, and +12V on both sides when there was no current draw.
    Swapping the fuse is a much faster and more reliable diagnosis.

    The word "fused" in other contexts means 'joined'. In electrical terminology it means a circuit protected by a fuse. The word 'fused' for the condition of a fuse is, at best, ambiguous.

    (A similar mis-used word is clutch 'engaged'. A clutch is engaged when it's joining the shafts, not when you press the pedal to *disengage* them.)

  17. #17
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    So when you actuate the fuel pump relay manually via inpa, the pump turns on, but there is no fuel pressure? Did I understand that right?
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  18. #18
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    There seems to be some confusion here regarding the fuel pump relay so let me clear it up. I can manually turn on the fuel pump relay via inpa, not the fuel pump. Even if I manually turn it on I still don't have a 12v signal at the fuel pump connection. I also have more than enough gas in the tank, I poured I'm 30 liters.

    I think it's a wiring fault, not an actual mechanical fault. I will retest the fuses and every other electrical connection in the fuel system. Will report back

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  19. #19
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    tested the fuses and found no faults, all of them test fine using a multimeter. Checked the ignition barrel and it seems to be working fine. The car sat with a disconnected battery and EWS for about 5-6 months so maybe my EWS is out of sync. The only problem I'm having right now is that INPA gives me an error the moment I try to sync it. When i try to realign the EWS-DDE it gives me an error and stops working. It tells me that it couldn't find the function and asks if i want to stop the script. any ideas what might be causing INPA to behave like that?
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  20. #20
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    Have you tried to see if INPA will communicate with the other modules in the car?
    If that works OK then it sounds like the EWS is shot.

  21. #21
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    Quote Originally Posted by ltpickles View Post
    .......... I can manually turn on the fuel pump relay via inpa, not the fuel pump. Even if I manually turn it on I still don't have a 12v signal at the fuel pump connection.......
    How do you know the relay turned on?
    If indeed the relay energized, there should be 12v at pump connector, regardless of DME-EWS sync. If there is not, there is a wiring problem or relay contacts are burned.
    JimLev posted a DIY w/photos on how to jump the fuel pump relay. Suggest you install this jumper and search for cause of no power at fuel pump connector. A jumper is the best way to energize fuel pump and trouble shoot FP issues. You remove the relay and install a jumper between pins 30 and 87

    http://www.google.com/url?sa=i&rct=j...12235167086421

    If there is a DME-EWS issue there will be a code for it.

  22. #22
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    When I energized the relay I had fuel pressure at the engine. I have a code for my ews system and I've been trying to realign it but I keep getting inpa errors. Everytime I try to sync I get the error "API error #98 job not found". I looked it up on the forum but can't find a anything conclusive.

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  23. #23
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    OK, I'm really confused........how you can have fuel pressure if you don't have 12v at the fuel pump connection as you said in post 18?

    For the INPA problem, post a question on one of the coding forums http://www.bimmerforums.com/forum/fo...ostic-Software or reinstall INPA.

    This link installs ISTA+ but you will also get INPA, NCSExpert, Tool 32, and WinKFP. It's one of the easiest installs I've ever found. Works on Win7 & 10.
    http://www.bimmerfest.com/forums/sho....php?t=1023698
    Last edited by pshovest; 12-01-2017 at 06:11 PM.

  24. #24
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    Post 18 is before I replaced my fuel pump. I can manually trigger the relay from inpa and get fuel pressure.


    Now the fuel pump is working I'm trying to figure out why the car won't start on it's own. It cranks, and gets spark but no fuel. I jumped the relay and ran the car for a few minutes so I know the injectors are also working fine. I will download that version and try communicating with ews. Thanks for all the help guys


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  25. #25
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    Post all of the codes INPA reports.
    Disconnect one of the fuel injectors. With ignition switch on, verify there is 12v at one of the fuel injector connector terminals when measured to ground.

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