Results 1 to 18 of 18

Thread: Low Voltage at terminal 30 for Fuel Pump Relay

  1. #1
    Join Date
    Feb 2012
    Location
    Irvine, CA
    Posts
    8
    My Cars
    1993 BMW 325ic

    Unhappy Low Voltage at terminal 30 for Fuel Pump Relay

    I'm experiencing a really odd problem. I'm a fairly new owner of a 92 E30 325ic and the car just died on my wife while on the road. I've checked for fuel pump issues and ignition issues as well as ECU issues. Here's what I know. There is only a reading of 4 - 5 volts at terminal 30 for the fuel pump relay. If I jump another 12V source to terminal 87 of the fuel pump relay, the pump starts up and the car runs fine, so I believe the pump is fine. If I try jumping terminals 30 and 87 to bypass the fuel pump relay, the fuel pump doesn't start up, I'm assuming due to the low voltage. I've also separately tested the fuel pump relay and it tests out fine.

    Does anyone know what could be the possible cause for the low voltage reading at terminal 30 for the fuel pump relay?

    Thanks,
    Andre

  2. #2
    Join Date
    Sep 2011
    Location
    chicago
    Posts
    271
    My Cars
    85 325e
    The fuel pump is a computer controlled ground if I recall properly, check the grounds. Also the DME Relay control is in front of that circuit, check that relay make sure that control coil isn't over consuming (or low voltage itself). Dont forget to check the basics :P clean terminals, solid grounds, etc.
    I like to test stuff before I replace it, it makes me feel better about expensive parts.

    idle thread

    Most recent discovery on my pre-owned e30: car has the ability to alter my lifestyle indirectly through use of my wallet.

  3. #3
    Join Date
    Feb 2012
    Location
    Irvine, CA
    Posts
    8
    My Cars
    1993 BMW 325ic
    Does't the BME relay control terminals 85 and 86 on the fuel pump relay? Those terminals seem to be working fine. I'm getting 12V on 85. It's just the 5V from terminal 30 that is puzzling me. If I jumper 12V into terminal 87, the fuel pump starts right up, and if I start the car that way, it runs.

  4. #4
    Join Date
    Sep 2011
    Location
    chicago
    Posts
    271
    My Cars
    85 325e
    Dme Grounds out fuel pump relay to make it work. Power for that relay goes through the DME relay's 30-87.

    Junction > DME Relay switched side > Fuel pump relay control side.

    That is the series tidbits, in parallel there is the purge valve and idle speed actuator.

    Right off the junction goes to the fuel pump relays switched side, then through a fuse at the front distribution block, then the pump.

    Junction > Fuel pumps switched side > Fuse > pump
    I like to test stuff before I replace it, it makes me feel better about expensive parts.

    idle thread

    Most recent discovery on my pre-owned e30: car has the ability to alter my lifestyle indirectly through use of my wallet.

  5. #5
    Join Date
    Feb 2012
    Location
    Irvine, CA
    Posts
    8
    My Cars
    1993 BMW 325ic
    But my problem isn't on the switch side on the fuel pump relay. I get 12 v from 86 when the car is turned on. Am I missing something? It's terminal 30 that's messed up. Shouldn't it always read about 12v? I'm just wondering what's upstream from 30 that could be causing the voltage drop.

    I've just found a wiring diagram that shows that terminal 30 of the fuel pump relay is directly connected to the battery. However, does anyone know if there are any spliced/ connectors in between?

    At this point I'm tempted to splice in a 12v source into terminal 30, but I'm concerned that I'm not addressing the root problem which may lead to a short circuit somewhere or a battery drain.

    Any thoughts?
    Last edited by tokky28; 02-18-2012 at 12:31 AM. Reason: Automerged Doublepost

  6. #6
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
    Moderator
    Join Date
    Nov 2008
    Location
    Lakewood, CO
    Posts
    9,942
    My Cars
    20 440ix cab, 12 X3 35ix
    You are correct that the power comes directly from the battery. It also has its own wire to feed it. Measure voltage at the battery by touching the battery posts. This is your baseline voltage. Now measure again using the (+) clamp and (-) post. If there is any change, clean the (+) post and clamp. Similarly test the (+) post and (-) clamp and clean as needed. Next, measure between the (+) post and chassis ground. I you see a drop here, clean the connection between the ground cable and chassis. The measurement between (+) and chassis ground will be your baseline for the rest of your measurements.

    I'm not sure how the rest of your system is wired as my iX has the battery in the trunk. Either your fuel pump wire goes directly to the battery clamp or it goes to a binding post on the firewall. Trace the wire that feeds the fuel pump and see where you get the drop at. It should be a 1.5 mm2 (~14-16 gauge) red wire. Common causes for voltage drops are bad connections, internal wire corrosion (usually at the connectors), worn insulation. It should be fairly easy to trace since the wire should be completely under the hood.
    "Howdy, Folks!"

    1986 Delphin 528e - Roof rack equipped lumber hauler.
    1989 Zinnoberrot 325iX Sedan - I miss this car. (Deceased)
    1998 Avus Blau 328iC - Someone else's project now
    2008 Platinum-Beige X3 3.0si - Current project
    2012 Alpine White X3 xDrive35i - My new snowmobile.
    2020 Estoril Blue 440i xDrive cabrio - This car is a blast to drive.

  7. #7
    Join Date
    Feb 2012
    Location
    Irvine, CA
    Posts
    8
    My Cars
    1993 BMW 325ic

    Red face

    Thanks for your response. My battery is located in the engine compartment. I don't think it's a ground issue since the voltage was tested across 30 and chasis. The hot terminal from the main relay socket showed 12v, so I guessing the issue has to be isolated to the wiring between 30 and the battery. I'm only seeing a couple of think cables to the battery itself. Could there be another connection that I'm missing?

  8. #8
    Join Date
    Dec 2004
    Location
    Huntsville, AL
    Posts
    25,923
    My Cars
    87 325is
    It sounds like there is a high resistance in the power supply line to the fuel pump relay. My docs show that connection to be from the ignition switch via C101 pin 6. Placing a jumper between 30 & 87 and tracing back to find the point that has system voltage will tell where the problem is.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

  9. #9
    Join Date
    Feb 2012
    Location
    Irvine, CA
    Posts
    8
    My Cars
    1993 BMW 325ic
    Thanks for your input Jim. I see that c101 is downstream from 87 towards the pump. But I'm pretty sure that my problem is upstream from 30 towards the battery. The pump runs fine if I jumper a 12v source to 87.

  10. #10
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
    Moderator
    Join Date
    Nov 2008
    Location
    Lakewood, CO
    Posts
    9,942
    My Cars
    20 440ix cab, 12 X3 35ix
    Quote Originally Posted by tokky28 View Post
    Thanks for your response. My battery is located in the engine compartment. I don't think it's a ground issue since the voltage was tested across 30 and chasis. The hot terminal from the main relay socket showed 12v, so I guessing the issue has to be isolated to the wiring between 30 and the battery. I'm only seeing a couple of think cables to the battery itself. Could there be another connection that I'm missing?
    If you don't find the red wire at the battery terminal, see if there is a junction terminal on the firewall near the battery. One or more of the (+) battery connections will lead there.
    "Howdy, Folks!"

    1986 Delphin 528e - Roof rack equipped lumber hauler.
    1989 Zinnoberrot 325iX Sedan - I miss this car. (Deceased)
    1998 Avus Blau 328iC - Someone else's project now
    2008 Platinum-Beige X3 3.0si - Current project
    2012 Alpine White X3 xDrive35i - My new snowmobile.
    2020 Estoril Blue 440i xDrive cabrio - This car is a blast to drive.

  11. #11
    Join Date
    Feb 2012
    Location
    Irvine, CA
    Posts
    8
    My Cars
    1993 BMW 325ic
    Guess what? I found the wire to the battery terminal and it was barely crimped in with a group of other wires. I pulled it off and sure enough, I lost the 12v to 30 on the fuel pump relay and an electrical connectivity test confirmed it. I'll be repairing the connection later today! Thanks for you help!

  12. #12
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
    Moderator
    Join Date
    Nov 2008
    Location
    Lakewood, CO
    Posts
    9,942
    My Cars
    20 440ix cab, 12 X3 35ix
    Awesome! I know that many people say a crimp connection is better than solder. However that all depends on the quality of the crimp. For myself, I always use solder and heat shrink tubing.
    "Howdy, Folks!"

    1986 Delphin 528e - Roof rack equipped lumber hauler.
    1989 Zinnoberrot 325iX Sedan - I miss this car. (Deceased)
    1998 Avus Blau 328iC - Someone else's project now
    2008 Platinum-Beige X3 3.0si - Current project
    2012 Alpine White X3 xDrive35i - My new snowmobile.
    2020 Estoril Blue 440i xDrive cabrio - This car is a blast to drive.

  13. #13
    Join Date
    Feb 2010
    Location
    MYRTLE BCH SC
    Posts
    1,045
    My Cars
    86 porsche 930, 88 325is
    Quote Originally Posted by richardodn View Post
    Awesome! I know that many people say a crimp connection is better than solder. However that all depends on the quality of the crimp. For myself, I always use solder and heat shrink tubing.
    i usually crimp and solder my connections. i have seen way too many bad crimp jobs, and with these cheap connectors, yes AMP, they need to be soldered.

    i have been round and round with guys on pelican about this. their big argument is " but aircraft only crimp their connectors"(not true). but aircraft connectors are much much better connectors and way more expensive.
    their other argument is that the wires can wiggle and break at the connector from the "stiff wire" caused by soldering. (then they are using way too much solder).
    nothing is 100%. but a crimp alone may only be 50 % reliable, add soldering and now you may have 75% reliability.

    sorry, had to vent.

    always give your crimped wires a good tug to see if it can pull out.
    [__] RUNNING: [__] NOT RUNNING: 86 PORSCHE 930
    [__] RUNNING: [__] NOT RUNNING: 88 BMW 325is 200K+
    [__] RUNNING: [__] NOT RUNNING: 2000 MERCEDES E320 WAGON
    [__] RUNNING: [__] NOT RUNNING:99 GRAND CHEROKEE 160K::
    [_:_] RUNNING: [__] NOT RUNNING: mazda B2200

  14. #14
    Join Date
    Jan 2013
    Location
    Ontario, Canada
    Posts
    3
    My Cars
    2004 325Ci
    Is anyone have fuel pump connector diagram or fuel supplying system? Mine are 4 wires (E46, 325Ci)

    If you have 12V at pin 30 and working fuel pump relay (tested off-line), shall you see 12V at fuel pump connector, just 3 to 5 sec. then voltage drop to Zero when switch keyON?

    If you have a bad connection (crimped) at fuel pump connector, how do remove and fix it?

    Hi ti36gold,
    When you posted Junction > DME Relay switched side > Fuel pump relay control side.

    Does it mean DME relay only in effect after the engine start and wired to pin 87 of fuel pump relay?
    or DME relay control voltage feed to pin 86?
    Last edited by tue22; 01-27-2013 at 09:51 PM. Reason: Automerged Doublepost

  15. #15
    Join Date
    Dec 2008
    Location
    Las Vegas NV
    Posts
    2,255
    My Cars
    91 318i 04 325i
    ^^ You'd have better luck posting in the E46 forum.
    On Christ the solid Rock I stand, all other ground is sinking sand. (Edward Mote 1797-1874)

  16. #16
    Join Date
    Jan 2013
    Location
    Ontario, Canada
    Posts
    3
    My Cars
    2004 325Ci
    Sorry for my previous question.
    Now I understand what ti36gold meant:

    Dme Grounds out fuel pump relay to make it work. Power for that relay goes through the DME relay's 30-87.

    Junction > DME Relay switched side > Fuel pump relay control side.

    That is the series tidbits, in parallel there is the purge valve and idle speed actuator.

    Right off the junction goes to the fuel pump relays switched side, then through a fuse at the front distribution block, then the pump.

    Junction > Fuel pumps switched side > Fuse > pump

    That could apply in my case when I do not have 12V at fuel pump connector. I may have to check voltage at pin 30, pin 85 of the fuel pump relay, and test DME relay as well.

    Just curious that where I can find the junction box of DME circuit and fuel pump circuit?
    Thanks.

    typo: should read pin 30 and pin 86
    Last edited by tue22; 01-29-2013 at 02:40 PM. Reason: Automerged Doublepost

  17. #17
    Join Date
    Nov 2023
    Location
    New Braunfels, TX
    Posts
    1
    My Cars
    1991 325i (my son’s)
    Hello. New to this forum and know this one is OLD, but sounds similar to issue my son is having w his 91 325i. He's getting no voltage at pin 30 of the fuel pump relay. We hadn't tested the DME relay yet - is it the first relay (closest to front of the car) in that same block? He does have pwr to the last relay (closest to driver).

  18. #18
    Join Date
    Sep 2007
    Location
    Regina, Sask, Canada
    Posts
    2,156
    My Cars
    82 320i 89 325i
    Quote Originally Posted by Bwiens73 View Post
    Hello. New to this forum and know this one is OLD, but sounds similar to issue my son is having w his 91 325i. He's getting no voltage at pin 30 of the fuel pump relay. We hadn't tested the DME relay yet - is it the first relay (closest to front of the car) in that same block? He does have pwr to the last relay (closest to driver).
    front to back is main / fuel / 02 sensor.

    also check the red wire on the battery and the fusible link it leads to.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •