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Thread: No spark. Trouble shooting ?s

  1. #1
    Join Date
    Dec 2017
    Location
    Chicago Illinois
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    410
    My Cars
    2003.5 E46 M3, 1992 e34

    No spark. Trouble shooting ?s

    Hey all, I just recently picked up a 1986 635csi with m30b34 motor. I have been driving around with no issues. Took her out last friday night and came home and parked it. Let her sit on charger overnight and when I went to start Sunday, after sitting all saturday , she cranked and cranked but no start. I jumped fuel pump relay and heard the pump and hears the injectors firing so fuel system is in order. Checked for spark and got nothing. Ive been reading through so many guides for no start but just can’t seem to get definitive answers.

    Im replacing the crank reference sensor because I know thats a major culprit. Im leaving the speed sensor for now because apparently car will still start if thats faulty. I tried two different millimeters and couldn’t get a sound resistance measurement off of these, I have no idea why.

    Now ive been testing the main relay and with ignition off I get no voltage at pin 30, but when ignition is on I get 12 volts at pin 87. Id like to replace the main relay as a precautionary measure but cant seem to understand, everyone says its 5 prong but mine is orange and only has 4 prongs. Do I have wrong one ?? See pictures. Can anyone link me the proper replacement.

    I also tried testing the ignition coil and could not measure any voltage off it with ignition on. I disconnected it and tested resistance and between pin 1 and 15 got .9 ohms, supposed to be .5 and between the main plug and 15 got 6. But it’s supposed to be 6k. My DMM was set to max ohm readings.

    Im pretty lost and am hoping I can get some insight. Could I have a bad ignition switch? Even though main relay reads 12volts when ignition is on? But coil doesnt? IMG_1683.jpg
    Main relay location per manual.

    IMG_1684.jpg
    4 prong orange main relay.
    Last edited by jmile46; 02-26-2019 at 12:40 AM.

  2. #2
    Join Date
    Sep 2007
    Location
    Redwood City, ca, USA
    Posts
    347
    My Cars
    2015 428i Coupe
    Check CW6er's response in this thread: https://www.bimmerforums.com/forum/s...ump+main+relay

    As I recall, the fuel pump relay has 3 prongs and the main relay has 4 prongs. I just sold my 6, a 1986, so I can't confirm.

  3. #3
    Join Date
    Dec 2017
    Location
    Chicago Illinois
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    410
    My Cars
    2003.5 E46 M3, 1992 e34
    Quote Originally Posted by ldk View Post
    Check CW6er's response in this thread: https://www.bimmerforums.com/forum/s...ump+main+relay

    As I recall, the fuel pump relay has 3 prongs and the main relay has 4 prongs. I just sold my 6, a 1986, so I can't confirm.
    I have read that post before! As for main relay I since checked again and realized my main relay is in different location. Its a 5 pin and silver. My main relay was mistaken for what is actually the oxygen sensor relay. Can confirm main relay gets voltage at pin 30 and 86. Proving obc relay and ignition switch? Is good? However I don’t get voltage at ignition coils. But with ignition on I get voltage at injectors. So maybe part of main relay is good, part isn’t?

  4. #4
    Join Date
    Sep 2007
    Location
    Redwood City, ca, USA
    Posts
    347
    My Cars
    2015 428i Coupe
    Check this post by CW6er for a description of all relays:

    https://www.bimmerforums.com/forum/s...ump+main+relay

    The fuel pump relay has 4 prongs, and the main relay has 5.

    The Electronic Troubleshooting Manual can be helpful: http://wedophones.com/Manuals/BMW/

  5. #5
    Join Date
    Feb 2009
    Location
    Pittsburgh, PA
    Posts
    1,718
    My Cars
    '86 635CSi, '08 128i
    Let me check out my trusty ETM...main relay gets battery power at terminal 30. Terminal 86 gets power from the OBC. Term 85 should be grounded.

    As for the coil, you should see power on terminal 15 from the ignition switch in run or start powsitions. DME pin 1 grounds coil terminal 1 to switch the coil.
    Save the manuals!
    '08 128i 6MT, '86 635CSi 5MT (B32, Motronic 1.3, WBO2, G265, 18# FW, 3.46 torsen)
    Past projects:
    '96 318iS, sold 4/23 '90 535iM, RIP 1/23 '90 535iA RIP 6/22 '91 318i, sold 7/19 '97 M3 sedan, sold 11/18 '85 735i, RIP 2/18 '92 325iC, sold 7/16 '91 318iS, sold 6/16 '84 745i, sold 10/14 '82 633CSi, traded 9/12 '90 325i, RIP '87 325 sold '89 525i, traded '87 325iS, RIP

  6. #6
    Join Date
    Dec 2017
    Location
    Chicago Illinois
    Posts
    410
    My Cars
    2003.5 E46 M3, 1992 e34
    Thanks for the help guys! Turned out to be the crank reference sensor! She’s back up and running!

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