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Thread: 1985 BMW 745i No Start

  1. #1
    Join Date
    Jul 2018
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    1985 BMW 745i

    1985 BMW 745i No Start

    Symptoms:
    1) Turns over fine
    2)Has fuel at the rail and spark but no start
    3)Tach bounces all over the place randomly when key is in start position. Doesn't do this while engine is turning over.

    Done so far:
    1) Spark plugs replaced
    2) New crank sensor
    3) New fuel pumps (In tank and in-line)
    4) Main relay replaced

    I don't know where to look next
    Last edited by AJTBMW; 07-28-2018 at 01:38 AM. Reason: First version was a mess

  2. #2
    Join Date
    Jan 2005
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    Japan
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    54,655
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    11/88 E32 750iL+98 E36M3
    Moved to E23 forum
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
    Join Date
    Jun 2010
    Location
    TX
    Posts
    4,487
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    1983/84/85 745i
    How long has this been sitting?

    Also, you have one massive paragraph. Break it up for us, it is entirely too difficult to read.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  4. #4
    Join Date
    Jul 2018
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    Wisconsin, USA
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    6
    My Cars
    1985 BMW 745i
    Its been sitting for somewhere around five years now. Ive been tinkering with it fixing what I have found that doesn't work and trying to track down the last issues.

  5. #5
    Join Date
    Jul 2018
    Location
    Wisconsin, USA
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    My Cars
    1985 BMW 745i
    In summary: Its a 1985 e23 that doesn't run. It definitely has spark and has fuel at the rail. It turns over just fine when I turn the key but wont start or sputter. Ive replaced the crank sensor and done fuel pump and line replace/repairs. I suspect the ECU but don't really have evidence to back it up so I'm not going after it yet. I don't know what else to check. More symptoms and information ^^^

  6. #6
    Join Date
    Jun 2010
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    TX
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    4,487
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    1983/84/85 745i

    Thumbs up

    Thanks.

    Hit each injector with 12V. Seen it many times, they could be stuck shut internally. ECUs die and pretty much always stop providing spark. You have this. Hell, spray in starting fluid.

    Car will NOT run without both reference sensors functioning on the bellhousing. One is a TDC marker and one is for engine speed. Make sure you have a good CTS.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  7. #7
    Join Date
    Oct 2007
    Location
    Valley Village, CA
    Posts
    624
    My Cars
    1985 745i
    Have a friend crank it for you while you hold a screwdriver up to each injector (with your ear at the butt end) to see if they click.

    I’m willing to bet the injectors are gummed up or not firing.

    Outside of that, make sure you don’t have any massive air leaks. Worst case get a compression test done.
    When your enemy is making a mistake, do not interrupt him.

  8. #8
    Join Date
    Jul 2018
    Location
    Wisconsin, USA
    Posts
    6
    My Cars
    1985 BMW 745i
    Update: Ive run 12v through each injector and got a nice click from each of them. Trying again a few times to start it, nothing seems to have changed. I double checked the live wires to the main relay and the fuel pump relay and both were good for both relays.
    Last edited by AJTBMW; 07-29-2018 at 05:34 PM.

  9. #9
    Join Date
    Jun 2010
    Location
    TX
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    My Cars
    1983/84/85 745i

    Thumbs up

    You sure the main relay is good and has correct dual 87 outputs? The green wire is the switched 12V trigger from the ignition switch and the outputs are the dual 87s which are red/blue and red/white. Can always jump the center three pins to verify the wiring is good.

    If you are sure you have spark, shoot starting fluid in the throttle body and see if it lights.

    Why did you replace one of the two sensors on the bellhousing? If you have them in the

    Battery terminals tight AND CLEAN? Is it fully charged and newer?
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  10. #10
    Join Date
    Jul 2018
    Location
    Wisconsin, USA
    Posts
    6
    My Cars
    1985 BMW 745i
    Ill test the main relay wiring again in the morning. It activates the new relay when I plug it in and everything down the line from it (**that I have checked) has the correct power etc..

    I replaced the sensor because I read that it was a common failure point in these cars and the one that was in there seemed to have been abused when someone tried to take it out and eventually gave up.

    I bought a new battery for the car right about a year ago and the connections are all solid and clean to it. Ive had it charged and tested a couple times over the last month most recently was the day I posted this original request for help.

    After verifying the main relay wiring is doing what it should Ill use some starter fluid. Ill update after that.

  11. #11
    Join Date
    Jul 2018
    Location
    Wisconsin, USA
    Posts
    6
    My Cars
    1985 BMW 745i
    I've found an issue. First of all, I removed the front right speaker and found the relay there to the motronic control was all nasty and rattles. I went to the auto parts store to find a replacement (it seems to be the same exact relay as the main relay). The only ones I found have the same diagram, but the 30pin and the 86 pin are flipped.

    I went back to the main relay that I replaced and found that it is flipped as well with the same diagram.

    Could anyone with this vehicle tell me the locations of the pins on their main relay?
    Last edited by AJTBMW; 07-30-2018 at 06:30 PM.

  12. #12
    Join Date
    Jun 2010
    Location
    TX
    Posts
    4,487
    My Cars
    1983/84/85 745i

    Thumbs up

    PM me with your cel number and I will text you a few pics.

    Center three pins on the main relay are the 30 and dual 87s. Just jump these and see if the car starts.

    Kickpanel relay is for the EH trans.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



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