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Thread: Bad Reference Voltage

  1. #1
    Join Date
    Jun 2017
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    Denver, CO
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    264
    My Cars
    325xi; 740i

    Bad Reference Voltage

    I have been chasing the same issue for the past two months about the car never idling above 500 acting weird at a specific temp etc. Today I was testing some voltages and sensors when I found what was supposed to be a 5V reference signal is not 5V but is instead 6.4V. How close to 5V is it supposed to be? If I understand my reading correctly then the DME has an internal component failure? I just went through the DME and re-soldered it and it did lighten the issue effect but some component may have given up already..
    New Daily:
    2011 Audi A6 Avant 3.0T prestige. 1 of 368

    ----FOR SALE-----
    04 BMW 325xi 143k


    The Fun car:
    94' BMW 740i 308k miles

    Fresh 72k mile engine with all new seals. True E34 Manual Trans Engine Harness. 6spd Transmission Swap, Getrag 420G. RHD LW Single Mass Flywheel. E39 M5 Clutch. E39 M5 Shifter. Factory Car Phone. Factory 6CD Changer. Factory Electric Sunshade. Not So Factory Factory Electric/Heated Rear Seats. E38 Heater Valves. E43 M5 calipers/brakes

    Sold:
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  2. #2
    Join Date
    Jul 2016
    Location
    Chicago, Illinois
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    3,842
    My Cars
    are slow
    Get another 404 DME, they're dime a dozen.

  3. #3
    Join Date
    Jun 2017
    Location
    Denver, CO
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    264
    My Cars
    325xi; 740i
    I have a feeling that is the cause of all my issues, it is perfectly fine with no adaptations but starts to act up when it adapts. My electrical engineer friend doesn't think the DME is bad but it is the only part that hasn't been replaced or verified working.
    New Daily:
    2011 Audi A6 Avant 3.0T prestige. 1 of 368

    ----FOR SALE-----
    04 BMW 325xi 143k


    The Fun car:
    94' BMW 740i 308k miles

    Fresh 72k mile engine with all new seals. True E34 Manual Trans Engine Harness. 6spd Transmission Swap, Getrag 420G. RHD LW Single Mass Flywheel. E39 M5 Clutch. E39 M5 Shifter. Factory Car Phone. Factory 6CD Changer. Factory Electric Sunshade. Not So Factory Factory Electric/Heated Rear Seats. E38 Heater Valves. E43 M5 calipers/brakes

    Sold:
    1996 Oldsmobile Aurora; 194k miles but with a bad paint job and dented fender resulting in a payout to buy the 740i

  4. #4
    Join Date
    Jan 2005
    Location
    Japan
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    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    Have you tested the air intake temperature sensor or replaced it?
    Not sure how that is on the M60, on the M70 we have one inside the MAF = # 1 http://bmwe32.masscom.net/sean750/MAF_v12/Bosch_MAF[1].gif and one of each side of the intakes near the firewall http://bmwe32.masscom.net/sean750/sp...enumIntake.jpg

    same with coolant sensor, on the M70 we have some, reporting to the cluster gauge, reporting to EML and reporting to the DMEs.

    In case you get a cheap used 404 DME you can test and swap. Always the best to have a spare unit on stock.
    Shogun tricks and tips for the E32 series are HERE!

  5. #5
    Join Date
    Jun 2017
    Location
    Denver, CO
    Posts
    264
    My Cars
    325xi; 740i
    The intake air temp is good. I just replaced the coolant temp sensor too. The 500 only idle I'm thinking is the DME, even the IAC is new and it made no change. There is no vacuum leaks either and the idle is dead steady at 500.

  6. #6
    Join Date
    Jan 2005
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    Japan
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    54,654
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    11/88 E32 750iL+98 E36M3
    Sorry, I only have plenty of spare DMEs and EML for the M70 pre-facelift -156 and facelift -352, but nothing for the M60 with the 404 number.
    Maybe someone here with a 740 has a spare DME and can lend it to you for testing. Also check in the E34 classifieds section if there is one for sale, there are some which always part E34, maybe one has a 540. But make sure it is then a 404, as some built years have a 484 and that does not work on your 404 (EWS/DWA)
    Shogun tricks and tips for the E32 series are HERE!

  7. #7
    Join Date
    Jun 2002
    Location
    Aberdeen, NC (yes, again)
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    My Cars
    E39M5, E500 4WD
    Hi Yukon,
    A very good friend of mine asked me to look in on your thread. I really need to know what sensor's wire is showing the improper voltage, and on what color wire. Furthermore, just to rule out various possibilities, do you have any other electrical issues or codes? What are the specifics of your car's odd behaviour?

    Just so you know, I generally hang out in the General Mechanical forum, so I might miss further posts here. I'd like to help though, so if you care to send me a PM with a link, I'll see if I can offer any thoughts.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  8. #8
    Join Date
    Jun 2002
    Location
    Aberdeen, NC (yes, again)
    Posts
    23,672
    My Cars
    E39M5, E500 4WD
    Hi Yukon,
    I have answered your PM, but for the sake of making this thread meaningful to anyone reading it later, I'm copying and pasting your PM, and my answer, here:

    Quote Originally Posted by yukon101
    Hello, thank you for your willingness to help. All the wires that are supposed to be a 5V reference are reading at 6V so TPS, IAT, CTS, ASC TPS. The issues that I have only occur before operating temp and the severity changes every day. To start it has never idles above 500rpm and I found my old TPS was bad, replaced that and no change but then these random issues started occurring. Some days I will pull up to a stop light before it is full temp and it will lean itself out too much, start bucking and nearly stall with a few cases of it stalling on me but starts right back up. Sometimes I will go from a stop, still before full op temp, and it will from what I can tell misfire like crazy then be fine, I can circumvent the misfiring by hitting the kick down switch and take off. The other thing it will do before op temp, which I am guessing on, the torque converter lockup with shudder which happened once. Before the problem temp the transmission will shift smooth as butter, at full temp it goes back to buttery smooth but at that problem temp (I can send a picture if need be) the downshifts are terribly rough but not dropping out of gears. The torque converter lockup is fine, no noises and I can cruise at 80mph 5th gear at 2k rpm. I used to get an O2 code 1221 (OBD1) but after I re-soldered the DME a week ago I have not seen a CEL. The issue is DME related, I did not pull the battery when I redid my DME to not reset the transmission adaptations without any adaptations on the DME the issue does not occur but starts to occur and slowly builds up in intensity as it starts to adapt. To completely throw a wrench in the works there are some days where it wont act up at all. I have replaced the TPS, CTS, ICV, and the cam position sensor.
    Thanks.

    If the car came to my shop with these issues, I would
    (1) smoke test the intake system. This engine is the leakiest thing BMW ever built, and all your symptoms point to this. Intake leaks affect behavior more when the engine is cold, in open loop, and can't adjust.
    (2) Use a slack-tube manometer, and test crankcase vacuum. Should be 3-6 inches of WATER. Normal vacuum testers measure inches of mercury. You can make your own slack tube manometer.
    page 8, post #183: https://www.bimmerforums.com/forum/s...lacement/page8
    (3) Clean and rebolt all major grounds, especially the one for the computers, and the engine ground .

    Forget the voltages, chase the symptoms you're dealing with.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

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