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Thread: Bmw 750il 1990 V12 half the engine running

  1. #1
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    Bmw 750il 1990 V12 half the engine running

    I have this bmw 750il 1990 since three years now and the last probleme is at the cold start check engine is flashing and just one side(bank) of the engine is running badly. if i disconnect the left mass air flow or the right coil wire the engine keep running badly if i disconnect the right mass air flow or the left coil wire the engine stop dead. when the engine get warm and at the time red check engine diapear the engine run smooth normal right away. i had it check at a garage with the obd1 and no code appear and all the parameters seem to be normal. After having read many post here it look like a cam sensor trouble or may be crank sensor? i'm not shure and if possible don't want to change things for nothing. I already change spark plug and wire , check cap and rotor and fuel line. I lost the post telling the resistence to have on the terminal of the cam sensor 500 ohms or so? And i'm wondering what is the way the 12 volts come before the cam sensor and is way after to the coil? I did look at many diagrams but it not to clear for me. Thanks and excuse my english, i'm better in french!!! André

  2. #2
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    11/88 E32 750iL+98 E36M3
    M30/M70 ignition system data accdg to Bentley
    Coil primary, coil code # 2051118335 terminals 1 (-) and 15 (+) resistance 0.50 ohm, Coil primary, coil code # 20510171101 terminals 1 (-) and 15 (+) resistance 0.37 ohm
    Coil secondary, coil code # 2051118335 terminals 15 (+) and 4 (ctr. resistance 6.0 kohm, Coil secondary, coil code # 20510171101 terminals 15 (+) and 4 (ctr. resistance 9.0 kohm
    spark plug ends 5.0+/- 10% kohm, shielded plugs 1.0 +/- 20% kohm, spark plug wires 0 ohm (approx.), rotor 1.1 +/- 10% kohm

    M70 firing order: 1-7-5-11-3-9-6-12-2-8-4-10, crankshaft position/rpm sensor: 540+/- 10% ohm

    http://www.bimmerboard.com/forums/posts/1072189/

    from workshop manual
    distributor rotor 1+/-20% kohm, angled/shielded connectors 1+/- 20% kohm, spark plug connectors 5+/- 20% kohm, cylinder identification sender coil resistance at 20 degree C (68F) <1 ohm, pulse sender/crankshaft position sensor coil resistance 540 +/- 0% ohm, temperature switch for e-box cooling E32 750: switch on at 44 +/- 3 degree C, switch off at 36 +/- 3 degree C.

    https://www.bimmerforums.com/forum/s...&highlight=cps

    are both fuel pumps running and producing enough pressure?
    You can also swop the ignition coils from one side to the other, bracket does not fit, but for a test o.k. One of my wrenching buddies had this last week, turned out that the old ignition coil sent too weak spark signals.
    same do with the MAFs, swop.
    The good thing on the M70 is that you can swop a lot of parts crosswise and find out the bad part.
    Is the EML light coming on first when you switch ignition on and then goes out?
    Ever cleaned the throttle valves? http://www.mwrench.com/Whitepapers/DKMotorcleanup.pdf
    Last edited by shogun; 12-02-2019 at 10:57 PM.
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  3. #3
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    Thanks for the informations i was looking for.
    I did not check fuel pump yet cause when the check engine is on i dont have spark comming out of one coil and when i disconect one camsensor the engine dont stop but keep running roughly than i think i dont have power on it . and when the engine get warm the check engine go out and the engine run just fine. And with no check engine on and the engine warm if i disconect a coil or a mass airflow or a camsensor on one side or th other the engine run badly.
    With the cold weather here in Quebec Canada now when i turn the key on the check engine come on even when i start the engine. In september the engine had a hard time to keep running with the check engine light on while it was getting warm and run fine after now the temperature here is under 32 degrees so the engine dont even keep running. i will make some test on a sunny day soon. Thanks again and give some news back.
    Last edited by shogun; 12-04-2019 at 11:41 PM. Reason: unnecessary quete remove, please use reply instead of reply with quote button

  4. #4
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    Check spark plugs 6 and 12, they are important, as the leads have the donuts, if these spark plugs do not spark, that makes trouble, because they are for the cylinder identification. Of course, # 12 is the most difficult to remove ;-)
    http://bmwe32.masscom.net/sean750/sp...arkPlug_12.htm
    or use a spark plug tester https://www.youtube.com/watch?v=UymD_i_9Q9Y
    This video demonstrates how to use a simple spark tester with an adjustable air gap to determine if the ignition spark is missing, weak, or intermittent. https://www.youtube.com/watch?v=IbzhxgD3ZUI

    For example the - popular among some M70 owners - MSD Blaster SS Coil PART# 8207 is advertised: "...when used with an MSD 6 Series Ignition, the Blaster SS produces 300 milliamps of current and a maximum voltage output of 40,000 volts! "
    The original Bosch coils are rated at 10,000 volts and best suited to firing copper plugs.

    Is your DME the M1.7 versions? Then read this, O2-Sensor Thermal Shock recall M70 engines https://www.bimmerforums.com/forum/s...ll-M70-engines
    Last edited by shogun; 12-05-2019 at 04:15 AM.
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  5. #5
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    Thanks again for the information. I will check to see if i got spark at the spark plug 6 and 12 with my tester. When i start it cold just the half of the engine have fire and after few minutes when the engine get warm both side got fire so it make me think that it look like a problem with camshaft sensor or crankshaft sensor cause it is affected by the heat of the engine. probably the ohms resistence is out of range when it cold and get back in the range whit the heat effect?? And i don't think a spark plug is affected by the heat, it work or not, right?
    Now i'm trying to follow with the electric diagram to see sequence of the power from the batterie to the spark plug, just to see from where the voltage come from before the camsensor and where it goes after...

  6. #6
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    Checking the 2 crankshaft sensors and the donuts/cylinder identification on ignition wire 6 and 12 should be the first thing to do. Then check the rest of the ignition system such as ignition coils, wires from ignition coils to distributors, distributors to distributor and so on.
    Do not forget to test the 2 fuel pumps. Maybe one is on the way out and starts slowly or has not enough pressure or volume.
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  7. #7
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    Today i did check the ohms resistence on the four connector and i have .490 ohms on just one connector the one at top left so i was shure that the other one at top right was
    the other crankshaft sensor and was dead but tonight on somes diagrams i realise that the two top connector are not the two crankshaft sensor automaticly . so tomorrow i will follow the wire of each connector to identify the cams and the cranks sensors. I got 12 volts on both coil but spark come out of just one. i disconnect the sparkplug wire no 12 cause it is on this side that the coil is not sparking and connect my spark test light at the end of it and there was no spark at the spark tester . no spark on the coil and no spark on the wire. i did that just to chek the fact that you did tell me that if the spark plug no 12 with the donnut on the wire is not sparking the signal will be not send.
    And yes the day i will have spark on both side of the engine i will check go to local garage to have both fuelpump pressure check cause matter fact is the problem with the check engine and fire on just one side did happen some day after i did fix a fuel hose leaking?? but as far as i know fuel problem can not cut the fire on one side of the engine?

  8. #8
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    Take these pics and the diagram for positions of CPS and CI https://www.bimmerforums.com/forum/s...6#post27839606
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  9. #9
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    Thanks again Shogun for all the goods informations. I replace the crank sensor no. 2 that i receive a week ago and the engine is running now!! The other problem i have now is the electriclock doors and trunk stop to work sudenly a few month ago. ear nothing when i use the key in any door and manualy the door locker is not moving at all. but the trick to raise all the windows when holding the door knob at the half and turning the key door is working so i imagine the electricity is in the doors? i did not look inside any door yet i was waiting to get some clue to know where to start first. the fuses seem tobe ok. my first idea is that the problem woukd be in the doorlock of the driving door, but why the thers door are not working independentely?i did not fond post for the 750 1990?

  10. #10
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    did you already check the fuses under rear seat left side? Locking is done by the GM general module and the relay module under rear seat left side, there are also fuses.
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  11. #11
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    I had a look at all those fuses and modules but i will check it more specificaly. what i know is that last winter i found some little pieces of shit of little mouses under that left right rear seat and in the glove box. And there was some wires that i did can see the copper of it so i did put some tape on these one i saw but i will go back to look at it. i did look at the electrical diagram but there is many fuses and many power comming from different device; ir remote, anthithief, electric lock and so on. but with your clue and the electrical diagram i will start with it. Thaks again

  12. #12
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    Locking is done by the central chassis module, we call it GM = general module and the RM = relay module, both under rear seat left side. The general module is the brain and the RM with the relays just executes the orders of the RM.
    Pics http://bmwe32.masscom.net/johan/elec.../rearseat.html
    Function diagram of the GM, in German language, but you can see the diagrams, easy to understand, ZKE E32 , #10 is central locking http://www.e32-schrauber.de/bmw/s-zke.htm

    Also the wire loom sometimes breaks between A-pillar and door, usually the driver door
    Attached Images Attached Images
    Last edited by shogun; 12-29-2019 at 02:13 AM.
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  13. #13
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    I did try to remove the general module and the relay module to have a look at it but i am not able to remove it.i did try to pull it they don't want to move . i did broke one screw they look like stuck in glue!!!??

  14. #14
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    GM and RM you can pull out , wiggle and pull, there are no screws/bolts or glue holding them, sometimes a bit difficult, so remove the modules/relays around the GM+RM to have a better grip and pull
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