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Thread: No Power to Fuel Pump, Relay & Fuse OK

  1. #1
    Join Date
    Sep 2007
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    Hamilton, OH, USA
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    16
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    1991 525i

    No Power to Fuel Pump, Relay & Fuse OK

    This is my first post so if I left off info please let me know.

    The car died as I was driving it, luckily as I was turning left into the driveway.

    I have a 91 525i, just bought a new fuel pump and installed it because the troubleshooting guide put the blame on the pump if the fuse and relay were ok. Both checked out fine.

    After the replacement, still no hum from the trunk. Naturally after buying the pump and installing, I saw where to check for voltage at the fuse. I did, the voltmeter shows no voltage to the fuse but OK at the relay.

    No evidence of a problem with the wiring harness or connections.

    When the key is turned a very small amount of voltage measures at the fuse and the pump harness, but no where near battery voltage, just a couple of tenths for an almost impossibly small instant then hits zero.

    Any ideas?

    Thanks

  2. #2
    Join Date
    Mar 2006
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    Huntersville, NC
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    1995 BMW 530i
    i had the same problem in my car. i replaced fuel pump, and still nothing happened. it turned out to be the crank sensor.

  3. #3
    Join Date
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    Quote Originally Posted by bimmerboy530i View Post
    i had the same problem in my car. i replaced fuel pump, and still nothing happened. it turned out to be the crank sensor.
    +1 Had the same thing happen.

    95 540i6 M Sport - 95 525it S52/OBD2 - 433k E36 328i5 - X5D that hit a pothole - IG: @justinmurray95

  4. #4
    Join Date
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    Hamilton, OH, USA
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    1991 525i
    I saw that, did the crank sensor fix it?

    Is there a diagnostic to check the sensor?

    Thanks!

  5. #5
    Join Date
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    It fixed my car. Check it with a multimeter on the ohm setting. It should read around 1250 ohms or 550 ohms. Some people have metered it at 550 ohms too.

    95 540i6 M Sport - 95 525it S52/OBD2 - 433k E36 328i5 - X5D that hit a pothole - IG: @justinmurray95

  6. #6
    Join Date
    Sep 2007
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    1991 525i
    Finally got the sensor out, it checks on tab 1 & 2 at around 1250 ohms, but not consistently.

    If I touch the magnetic end with something steel, it changes but sometimes sticks.

    Do you know if the ohms read constant on pins 1&2?

    I hate to replace another part if its good, ?

    Could anything else do this?

  7. #7
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    i replaced the sensor and it worked. i tryed reading with a voltmeter but i wasnt sure if it was good or not, so went ahead and bought a new one. if your sensor has a metal cap, its most likely to be original, and it might be burned out. i believe the new sensors are plastic all around.

  8. #8
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    Quote Originally Posted by triviaman View Post
    Finally got the sensor out, it checks on tab 1 & 2 at around 1250 ohms, but not consistently.

    If I touch the magnetic end with something steel, it changes but sometimes sticks.

    Do you know if the ohms read constant on pins 1&2?

    I hate to replace another part if its good, ?

    Could anything else do this?
    That is right then. It should be around 1250 ohms +/- 50 ohms. When you test it does it stay around 1250 ohms or is it all over the map?

    95 540i6 M Sport - 95 525it S52/OBD2 - 433k E36 328i5 - X5D that hit a pothole - IG: @justinmurray95

  9. #9
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    1991 525i
    There are times when the resistance measures zero, other times measures 1250. Changes when I pass something that the magnet can pickup. I cannot measure resistance predictably, where the pickup measurement varies by distance to a steel part, etc.

    Seems like it should have a bottom value.

    The switch is one of the old metal housing models.

  10. #10
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    I'd change it then. The worst thing that can happen is the car not run. Autohuaz AZ has them for $45 + shipping. Order $5 more in parts and shipping is on them When I metered mine the value was all over the map.

    95 540i6 M Sport - 95 525it S52/OBD2 - 433k E36 328i5 - X5D that hit a pothole - IG: @justinmurray95

  11. #11
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    BTW, motronic wont give the FP power until the engine starts to turn.

  12. #12
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    Quote Originally Posted by Goathumper View Post
    BTW, motronic wont give the FP power until the engine starts to turn.
    True. I was told by a friend that the pump will prime but if the CPS (a bad CPS or something much bigger) does not sense rotation the pump will not turn on.

    95 540i6 M Sport - 95 525it S52/OBD2 - 433k E36 328i5 - X5D that hit a pothole - IG: @justinmurray95

  13. #13
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    1991 525i
    Thanks again. I thought the fuel pump ran a little once the key was turned on but not in cranking position.

    I used to remember hearing that pump or something before cranking the engine over. My Bronco does that for sure, but it's much louder. I honestly can't recall hearing the fuel pump operate with the key in the on position for a second or two.

  14. #14
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    you will hardly hear a properly working fuel pump but it will prime for 2 seconds when the key is turned to pos. 2

  15. #15
    Join Date
    Sep 2007
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    Hamilton, OH, USA
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    1991 525i
    Priming does not occur now.

    Plan is to replace the crank sensor, but I don't understand how that impacts the priming sequence, just in case that does not work - what's next is a little ground lead off of the ignition wiring near the fuel rail.

    Any other ideas?

  16. #16
    Join Date
    Sep 2007
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    Hamilton, OH, USA
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    1991 525i

    New Information on problem!!!

    I checked the wiring based on the color codes, and found the ignition relay out of position. I was checking the wrong one...Jumpering 30 to 87 allowed the pump to run this time.
    I attempted to start the car with the fuel pump jumpered and it behaves like no spark. You can hear the fuel enter the engine thru the injectors.
    Tried to probe 85 to ground, got no continuity with the key in the start/run positions.
    With a relay in place the fuel pump does not prime when the key is first switched on before attempting to crank.
    Is there a permissive in the system that prevents 85 from working, can this wire be bad, or is the DME shot?
    Thanks for your help
    Jay

  17. #17
    Join Date
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    89 535i, 02 x5s, 03 530i
    CRANK SENSOR basically tells the computer everything is turning right and start sending signal to fuel pump, fuel injectors, ignition (spark)and such. I have fought, probed,checked every wire coming out of the DME this many times with the M20, M30 and M88 engines. sometimes they just had a bad spot in the wiring at the plug on the back of the engine. it doesn't matter on where you scrounge one either. just make sure that they are plugged into the proper plug (one has a white ziptie) the only difference between the different models of cars in the 80's and 90's is the length of the wire between the sensor and the plug, the E30's are shorter, so that gives you quite a few at junkyards to pull from E30:325,325e,E28 and E34:525,528e,533,535,E23 and E32:733,735,E24:633,635,M6,E28:M5. Since these are in the back of the motor, by the hood seam you might want to clean out the contacts and coat them with dielectric grease. what you are describing in your last post was always happening but you were focused on the pump issue. the injectors may flow some fuel but you will not go into the pulse pattern untill the pickup registers the flywheel turning so to not flood the engine. change the crank sensor

  18. #18
    Join Date
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    Hamilton, OH, USA
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    1991 525i
    My plan is to replace the crank sensor and a couple relays just to be safe regardless of other issues.

    From a troubleshooting standpoint, does the crank sensor impact the priming sequence? I have not heard or read anywhere if that requires a good crank sensor. Currently there is no priming at all. Does that protective circuit detect a problem with the sensor and hold out the relay even when the key is in position 2?

  19. #19
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    I have never had any luck getting the fuel pumps to run when the CPS was bad. Or maybe all the hacking I did on the wiring . Still, on the relays, make sure you use the exact replacement. it's pretty easy to drop in the wrong one and chase your tail for a couple of days when you do.

  20. #20
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    Quote Originally Posted by uberkarldrei View Post
    I have never had any luck getting the fuel pumps to run when the CPS was bad. Or maybe all the hacking I did on the wiring . Still, on the relays, make sure you use the exact replacement. it's pretty easy to drop in the wrong one and chase your tail for a couple of days when you do.
    I had the same issue. When I jumped the terminals it did not work right, lol. Sometimes it can get confusing.

    95 540i6 M Sport - 95 525it S52/OBD2 - 433k E36 328i5 - X5D that hit a pothole - IG: @justinmurray95

  21. #21
    Join Date
    Sep 2007
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    Hamilton, OH, USA
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    1991 525i

    New information

    I replaced the CPS and relays. No start.

    Checking for spark...

  22. #22
    Join Date
    Oct 2007
    Location
    Cincinnati, Oh
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    M5
    Mine is doing the same thing. Where is the crank sensor located on the motor???

  23. #23
    Join Date
    Oct 2007
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    Cincinnati, Oh
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    M5
    can you tell me where cps is located and what the part # is????
    Quote Originally Posted by atl530i View Post
    It fixed my car. Check it with a multimeter on the ohm setting. It should read around 1250 ohms or 550 ohms. Some people have metered it at 550 ohms too.

  24. #24
    Join Date
    Oct 2007
    Location
    Cincinnati, Oh
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    M5

    part #

    I contacted Autohauz and they couln't find part. Do you still have Part # ?????[quote=atl530i;10684603]I'd change it then. The worst thing that can happen is the car not run. Autohuaz AZ has them for $45 + shipping. Order $5 more in parts and shipping is on them When I metered mine the value was all over the map.[/quote]

  25. #25
    Join Date
    Jul 2005
    Location
    Newton, MA
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    91 318is, 98 318ti M CA
    Guys, when you go to your car, turn the key to "ON" position, dont crank it and listen for the fuel pump. I guarantee you the fuel pump will run.

    Unless you know for a fact that the fuel pump runs off of DME, dont post info. It runs on a separate loop, although the relays might be on the harness.
    I used to have to parallel park myself

    1991 318is: 95 M42 Motor + serpentine belt change, HR Sport Spring set + Bilstein sport shocks, E30 M3 CABs, misc TBD (lots of refreshing to do), Garaged (for now)

    1998 318ti: California + Sport factory packages, S52/3.2L w. OBD II OEM Retrofit, Supersprint European Exhaust modified for the TI, ZF 320 Transmission, Aluminum Flywheel with M5 clutch, 328i driveshaft, 2.93 Med Case E30 LSD w. E30 half shafts, Front M3 OEM suspension w. E36 M3 front brakes and stock front M3 sway bar/Rear E34 calipers w. stock 318ti rotors. OEM Bosch Aim Adjustable Projector Headlights, Pioneer DEH 80PRS, A/D/S PH15.2 Amp, Infiniti Cappa Perfect Speakers + X-overs + A/D/S 320is speakers + X-overs, Custom Molded Sub Enclosure in the trunk with a Nakamichi Sub

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