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Thread: 1991 BMW 750il wont start! Mechanic stuck! Been in shop >8 months!

  1. #1
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    1991 BMW 750il wont start! Mechanic stuck! Been in shop >8 months!

    First of all thank you all for taking the time to read through this post and any help/direction you may provide is greatly appreciated. I will try to be as detailed as possible and answer all questions the best I can.
    I am the owner of the vehicle and have had the car in the family for over a decade. Over the years we have done a lot of work to the car blower motor, interior cabin air filter, rear self leveling shock, front suspension, power steering pump and hoses, radiator and expansion tank, thermostat , clutch fan, etc. Car has always been very reliable and never not started right up.
    Since taking over ownership of the car from my father, I decided to do some things to the car as maintenance, since I knew certain things were still original to the car and could use being replaced. One day I was replacing the intake boots and of course the cracked old ones shatter and break as I am taking them out.. I replaced with new and later on the car basically goes into limp mode and misfiring as a piece of the old boot got stuck in the throttle body (which I did not know at the time) . Since I had about $4k in new parts to install in the car and not the time to do all the work (wanting it done sooner than later), I had the car towed to a friend of mines shop here in Dallas tx where the work would be completed by a BMW master mechanic . This was approximately 8 months ago now that I had the car towed there with all the parts to be replaced.

    I was doing the entire ignition system, heater core and hoses, pcv valves,fuel filters and lines, spark plugs, valve cover gaskets, engine valley plate, and some other things as well I cant think of off the top of my head. After my mechanic competed the work and put everything back together he has been unable to get the car to start. I asked him to do a detailed write up of the problem and what he has done to troubleshoot it so far. He sent me an email over this morning with his write up which I will share with you all for any input you may have as to the problem or what he can do next to figure out the issue, I have spent way too much money and let way too much time go by for this car to be sitting this long! Most recently I had both DME's sent off and completely redone, which costed me 832$. I was very surprised that the computers were bad, as they seemed to be fine before and never had issues, but I was not unwilling to count it out. But after getting them back and hearing from my mechanic the car still will not start and he does not know why I am at a loss for words. I thank you all for your useful input. And Thanks Shogun for showing me where to post this! Ill Copy and paste the email from my mechanic below..

    Vehicle was brought in with:
    • Multiple miss fire and EML code present.
    • Inspection showed part of air boot wedge in throttle plate left bank( drivers side ).
    • No other codes noted at this time.



    Vehicle repair was performed as noted:
    1. All spark plugs were replaced along wires ,cap and rotors both banks
    2. Valve covers gaskets were replaced
    3. Engine valley plate was replaced and sealed
    4. Intake risers were replaced both banks
    5. Crankshaft sensors were replaced with aftermarket tpi sensors
    6. Electric loom from positive post engine compartment to alt. was replaced
    7. Rear engine coolant by-pass pipe was resealed and temp. sensors were replaced with new units
    8. All heater and coolant hoses were replaced
    9. Along with heater core and pipes to core
    10. Oil change
    11. At this time vehicle coolant system was pressure tested for leaks none found
    12. Vehicle start was attempted with no results
    13. Inspection of systems showed no crank reading from right bank sensor unit was ohm -ed with passing results
    14. Inspection of DME relay circuit showed no ground at relay 1 on trigger side of relay. Relay was tested and replaced .
    15. Further inspection found continuity of wiring to relay but no signal from DME. Units were sent out and reman. To specs.
    16. At this point further inspection of engine controls is required results to follow.



    Again, any advice is appreciated. I was hoping with the help of this forum we can solve the issue together and I won't have to take the car to someone else or try to do it myself.

    Best,
    Max

  2. #2
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    5 - bad move, go OEM.

    What wire set? Are the spark pick-up donuts installed properly on the proper wires??

    Were the O2 sensors replaced at any point before issues started?

    How about the crank sensor connectors up at the top front of the engine? Same for those just mentioned donuts sensors? While not easy to do, they CAN be crossed over. Honestly, the car needs to be in proper hands. Remember, most of the stuff is reversed. That is the driver side throttle is for the passenger bank, etc. Its not straight forward for anyone unfamiliar with the engine.

    Was timing checked. Easy enough to do really since you can set it to zero and use the distributor rotors as a visual aid. I think pics are online of them at default position.

    And yeah, I have doubts the computers were bad. Sounds like an legit input issue.

    Wish you were closer, I would dive right into that thing.
    ______________________________
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  3. #3
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    when ignition is on, does the EML light come on and then disappears or stays on, or never shows up?
    M70 cps and pulse generator identification http://www.bimmerboard.com/forums/posts/1237505
    Did the shop check the fusable links? First 2 pics = fusible link A http://www.bimmerboard.com/forums/posts/377728/
    especially fusible link a which is an inline fuse from the battery to the engine bay. X6400 is the power post inside the E box = right side engine bay where the DME's and the EML are. It feeds only DME loads.ETM page 1367-00 for M70. Fusible Link A is 50 Amps.
    Fusible B is 80 Amps. It feeds all the Rear Power Box loads.

    Test at the diagnostic port pin 14 , pic here https://www.bimmerforums.com/forum/s...5-OBD-Port-Mod
    pin 14 is signal 30 B+ and should have minimum voltage of 11.75V, wire color RT = red
    Test at the power post inside the DME box.

    What happens to the DKs throttle valves when you switch ignition on? Are they moving a bit and then go back to default? Or no movement at all?
    General info about what to check in my old rough idle - no power thread http://www.bimmerforums.com/forum/sh...idle+now+power

    Maybe the person in charge at the shop can register here on the forum and directly communicate with us.
    Last edited by shogun; 08-23-2018 at 10:02 PM.
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  4. #4
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    thanks for your response! I figured tpi would be fine, do you think I need to switch? The O2 sensors were replaced in yrs past with no issues. I will have him recheck the crank sensor connectors and donut sensors. I don't know if he has checked the timing but can find out as well. How far away are you? LOL at this point its almost worth flying someone in to look at it

  5. #5
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    Shogun I have forwarded him all this info and encouraged him to join the site so he can communicate directly as well. I know he said he checked the fusible links but I will confirm tom with the info you provided. He said the DKs throttle valves are moving when you turn the switch on. I believe they move and then go back to default but can confirm tom. I really appreciate all the help from everyone and will update with more info soon!
    Thanks again!

  6. #6
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    O2 sensors are not that important, they will not stop the engine or cause a no start.
    Timing: here are pics how to reset the timing, I assume the shop has not touched that https://www.bimmerforums.com/forum/s...2-Valve-Timing
    TPI crankshaft position sensors: new to me, never read that someone installed them on his M70. Without proper installed and working CPS the engine will not work.
    Measure the crankshaft position sensors and see once more if they are properly connected, see my above link. crankshaft position/rpm sensor: 540+/- 10% ohm
    CIS sensors aftermarket: https://www.bimmerforums.com/forum/s...er-at-high-RPM
    importance of correct installed donuts https://www.bimmerforums.com/forum/s...5#post29640785

    Let the person in the shop register on the forum, so we can communicate directly with him.
    Last edited by shogun; 08-25-2018 at 11:55 PM.
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  7. #7
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    Waiting to hear back answers from mechanic. Encouraged him to join the site as well to communicate directly with you all. After going back and looking at the order I made from autohauosaz I noticed that the Crankshaft position sensors I purchased were made by facet and I must have accidentally purchased an extra set of camshaft position sensors which are made by TPI (part number CAS1177). The new set of spark plug wires from Karlyn STI came with new sensor as well so the TPI camshaft sensors were never installed which I was able to confirm today. Ive heard only good things about the Facet Crankshaft sensors and Karlyn STI plug wires.

  8. #8
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    IMG_4108.jpgTh
    Attached Images Attached Images

  9. #9
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    Double check the crankshaft position sensors installation, the gap of the sensor (see workshop manual), test them, see if they are installed correctly https://www.bimmerforums.com/forum/s...ex-Sensors-M70
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  10. #10
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    i suggest you to go to salvage yard and get a DME from similar car.

    does it crank but wont start?

  11. #11
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    DME's were repaired/check for a lot of money already!
    Most recently I had both DME's sent off and completely redone, which costed me 832$. I was very surprised that the computers were bad, as they seemed to be fine before and never had issues...
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  12. #12
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    did the repairshop tested the "repaired" DME and confirm it works?, anyway, its just a suggestion, for once (not a bmw related) i did send my electronics to a repair shop, charged me certain amount and claim it "fixed" and it never did, just paid the shop for nothing.

  13. #13
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    Why did your mechanic go right after the DME when no spark signal was found instead of the crank position sensor? Even if it Ohm'ed out, I would have double checked it with a known good one. Between the DME and the CPS, I would look at the CPS every time. I am not as familiar with the M70, but does it have a Crank position AND cam position sensor located in about the same place as the m30? My M30 had a crank sensor fail and I played hell figuring out what the issue was after replacing it. I had swapped the harness connector between crank and cam positions sensors.
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  14. #14
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    not knowing all the details what the mechanic did, but if it would be my car I would start first in the area of CPS and cylinder identification/donuts.
    Especially if the DME is version M1.7 with Bosch end # 352 and the car is equipped with the cat protect system, then the CI's must even work on cylinders # 6 and 12, otherwise the cat protect system makes trouble.

    Motronic M1.7 Catalytic converter protection function - ignition circuit monitoring https://www.bimmerforums.com/forum/s...ll-M70-engines

    To check a CPS with an ohmmeter is just a simple and dirty test, but not 100% accurate. Best is sensor output signal oscilloscope diagnosis as done by the pro shops.

    @Avec: the M70 has 2 crank position sensors and 2 cylinder identification sensors/donuts, 1 on cyl. 6 and the other on cyl. 12. Basically the same system as the M30 6-cylinder engine, just all parts x 2 for the V12.
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  15. #15
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    Would failure of a single crank sensor kill the signal to the DME?

    Also, the Crank and Cam sensor could be plugged in wrong on both banks. Just done wrong on one side, and it used as reference for the second
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  16. #16
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    Without a signal from the Cylinder Identification Sensors (CIS, referred to as CAMshaft sensors erroneously) the engine will start and run for 1 -2 seconds in 'lost spark' mode, firing the plugs on both the compression and the exhaust stroke - after that period the DME will shut off the injectors to stop wash-down as it cannot determine if the engine is firing.

    If the engine doesn't run for a couple of seconds discount the CIS's

    The most important check is to see if you have 12V on each coil in ignition position II - if you don't then the next thing to check is the two fuseible links as these provide power to the coils (along with a lot of other points).

    One CRANKshaft sensor will run bank of the engine irrespective as to what the other bank is doing.
    Last edited by Timm; 08-28-2018 at 04:34 PM.
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  17. #17
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    Thanks you all for the responses and help. Will answer as best I can with the info I'm being fed from the mechanic working on it. I assume he went to the DME instead of the CPS because they were both just replaced with brand new facet sensors ( now I think I should have bought BMW sensors). Mechanic checked placement of all sensors and says they are correct and said he has been using alldata as reference for placement. He said the gap on the sensors are fixed by attached mounts with no adjustment. Both coils have voltage and he checked both fusible links... the one in the engine compartment and the one at the battery. The engine cranks but will not start. Trying to get mechanic to Verify that the CPS are functioning properly via tests Shogun provided.

  18. #18
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    part0_2.jpg
    photo sent from mechanic

  19. #19
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    Need a very clear, full-frontal pic of the four connectors at front top center of engine. They are the crank and spark pick-up sensors. Photo MUST include some idea of where the wires head off towards. Two will go down the passenger side for crank. The other two will go off to those sensors pictured above.
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  20. #20
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    Also ask the mechanic if the fuel pumps are working and if he tested them. Testing
    http://bmwe32.masscom.net/sean750/fu...t/Fuelpump.htm
    http://bmwe32.masscom.net/sean750/fu...Regulators.htm
    I usually test the fuel pumps with ignition off and use a wire from B+ post engine bay left side and hold the other end briefly on top of fuse 23 and then on 24. That should activate the fuel pumps. As the engine is not running you can hear the fuel pumps running. Test the fuel hoses before and after by squeezing them with your fingers as shown in the link above. These fuses are called injection electronics in the wiring diagram.
    Note the the relais are in different locations by built year, K210, K211, K212, K213 = fuel pump relays and main relays
    up to 1988 built year http://www.e32-schrauber.de/bmw/date.../arb_08_88.pdf
    and then up to 1994 http://www.e32-schrauber.de/bmw/date...8_88-07_94.pdf
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  21. #21
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    Fusible links in trunk?

  22. #22
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    Quote Originally Posted by JDP530 View Post
    Fusible links in trunk?
    No fusible links in trunk on the E32, they are under rear seat passenger = right side and they already checked. One fusible link feeds the fuse box under driver side rear seat, the other one goes to engine bay and feeds the e-box.
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  23. #23
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    +1 on CPS.

    Best to use Bosch Original parts because this is a challenging electro-mechanical design. The electrical resistance of 540 ohms proves that there are MANY turns of thin copper wire! And the magnetic materials must be precisely crafted.

    The DME will refuse to fire any cylinder if it has any doubts about the position of the crankshaft. And properly so - we must never spark over a rising piston!
    Last edited by E32FAN; 09-07-2018 at 11:36 PM.

  24. #24
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    there's a 750il at the yard here in Dallas. where are you located? i'd be interested in helping.

  25. #25
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    Sorry for my absence . been very busy. and unfortunately not much progress has been made. I suspect my mechanic is not really working on it much. Shogun he said he has checked all the fuel pumps and that they are functioning properly . we replaced both fuel filters and fuel lines and are getting gas flowing as it should. he did say one off the filters appeared to be clogged when he replaced months ago. haven't really been able to get any info if he tested for proper cps function. Im getting fed up and at the point where I would take it to anyone to get fixed. I recommended even taking it to the stealership at this point and my mechanic said he was just at the dealership and in contact with his contacts over there and saying that they are stuck on an 850csi they can't fix. so basically saying they won't be able to fix it either. my concern is I feel like he is not working on it and sorta giving me run around. 10 months. now he has had the vehicle. MKIVJZA80 would take any and all help with open arms . The vehicle is located at the mechanics shop near garland . Name of shop is Advanced auto dynamics

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