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Thread: 1991 850i No Start/Won't Stay Running

  1. #1
    Join Date
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    1991 BMW 850i

    1991 850i No Start/Won't Stay Running

    I'm starting a new thread to just focus on the one issue with this 850. It won't stay running. I got this car for free and I really want to get it running and am thinking about restoring it in some shape or form.

    After replacing various parts, it will run but only for a second before stalling. Video of what its doing here (sorry its sideways): https://www.youtube.com/watch?v=HmBXXo4xWKA

    What I Know:
    -It has spark
    -It has plenty of fuel flow (have not been able to test pressure)
    -All Fuses are good
    -Seems to be no codes

    What I have replaced:
    -Both bad fuel pumps
    -Fuel hose that was leaking in sending unit and after fuel filters
    -All Plugs
    -Plug wires/ID sensors
    -Both crank sensors (one for sure was bad)
    -Known Good used FPRs
    -GM Capacitors (not related to starting)

    I need any advice now on where to go next. Hopefully the video will help you understand whats happening. Help me save her!
    Last edited by breeves002; 05-26-2016 at 12:23 PM.

  2. #2
    Join Date
    Feb 2013
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    95 840CI 91 850I
    If it were me I would get the number off the EML and buy a known good one with the same number. Should not be much and if it fixes it great if not you have a spare.

    I had a car with a bad EML and it did crazy stuff once the good one was plugged in everything got better. It did not show EML light.

    IF you have Compression, Fuel and spark it should start. If not then it has to be something that is not telling the fuel injectors to fire off after the initial start. If timing was screwed up and you keep cranking there would be misfires.
    Last edited by 2001740il; 05-26-2016 at 12:19 PM.
    BMW CCA #500359 E31 Chapter.

  3. #3
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    I was actually over another owners house on Tuesday diagnosing a very similar issue.
    He had replaced both fuel pumps but the car would not start, we had spark and no codes.
    It turned out to be a blockage in the fuel filters and lines, the fuel filters were never replaced. Also he had leaks in the fuel pump assembly lines.
    There was some fuel flow coming out but pressure was not adequate.
    Replacing both fuel filters and running the fuel pumps manually after fixing pressure leaks in the assembly solved the problem.
    It now runs on all 12!

  4. #4
    Join Date
    Apr 2016
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    1991 BMW 850i
    EML = Engine Management Light?

    Do you mean DME? This is an 850 so I would need two DME's.

    I will add that unplugging one DME it acts similarly. Starts up on 6 cylinders then turns right back off.

    - - - Updated - - -

    Quote Originally Posted by dragon850 View Post
    I was actually over another owners house on Tuesday diagnosing a very similar issue.
    He had replaced both fuel pumps but the car would not start, we had spark and no codes.
    It turned out to be a blockage in the fuel filters and lines, the fuel filters were never replaced. Also he had leaks in the fuel pump assembly lines.
    There was some fuel flow coming out but pressure was not adequate.
    Replacing both fuel filters and running the fuel pumps manually after fixing pressure leaks in the assembly solved the problem.
    It now runs on all 12!
    I need to just check the pressure. My gauge is really wanting to leak which is causing problems. I'll get the pressure checked at the filters. Maybe my problem is just fuel pressure... I definitely have plenty of flow. Once I fixed some fuel hoses that were busted, the car would actually start and not just chug and try to start. So its definitely better.

  5. #5
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    Quote Originally Posted by breeves002 View Post
    EML = Engine Management Light?

    Do you mean DME? This is an 850 so I would need two DME's.

    I will add that unplugging one DME it acts similarly. Starts up on 6 cylinders then turns right back off.

    - - - Updated - - -



    I need to just check the pressure. My gauge is really wanting to leak which is causing problems. I'll get the pressure checked at the filters. Maybe my problem is just fuel pressure... I definitely have plenty of flow. Once I fixed some fuel hoses that were busted, the car would actually start and not just chug and try to start. So its definitely better.
    BMW 850 had 2 DMEs and 1 EML module.
    So have you replaced fuel filters?? That might be your problem.

  6. #6
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    95 840CI 91 850I
    You have one EML and Two DME. Take the EML out record number and go hunting. It is located in the same box as the DME's.

    I thought you checked the fuel pressure at the regulator rail and it was good. Fuel pressure guage and T with shrader valve not very expensive and not too difficult to do.
    BMW CCA #500359 E31 Chapter.

  7. #7
    Join Date
    Jul 2009
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    Del Mar, CA
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    91 850i, 01 740i, 06 760
    You should measure the fuel pressure at the fuel rails. Harbor Freight has an inexpensive meter that will do the job. If that is good i would connect an oscope to the injectors to determine if they are being shut off.

  8. #8
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    Will report back tomorrow with findings if its not raining tonight.

    EML is the third computer in there, got it.

  9. #9
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    1991 BMW 850i
    Update:

    3 videos for your viewing pleasure.

    *seems* that fuel pressure is OK on both banks. Its oddly wild to me. I feel like it shouldn't be so uneven?

    Looks like injector pulses are being stopped by the DME for whatever reason and that is why the car stalls. I didn't feel like pulling the o scope outside since it looked like it was going to rain so I just used the test light. Works just as well for this although not nearly as much resolution.

    Something started squeaking today that hasn't done it before after the engine starts.

    Is EML a valid possibility? I really don't want to just throw parts at it.

    FP Bank 1: https://www.youtube.com/watch?v=-GjHM8zNEng
    FP Bank 2: https://www.youtube.com/watch?v=wbTU4Bqq59g
    Injector Pulses: https://www.youtube.com/watch?v=FkUANJjBJnw

  10. #10
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    I would say next step is EML as mentioned above.


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  11. #11
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    Couple things, you did not say if fuel filters have been changed?
    You still might have a blockage judging from fuel pressure being uneven, also the fuel pressure droops off too fast IMO, you might have a leak at the lines in the fuel pump assembly.
    We still don't know what the codes actually are, INPA never was connected?

  12. #12
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    That looks like you are getting no signals from the Cylinder Identification Sensors (the devices on plug wires 6 and 12). If the DME's don't get a signal after a second or two they turn the injectors off to stop wash-down of the cylinders. By the way, the fuel pressure should stay at 2.5 Bar or so at the fuel rail when the engine is not running for weeks - the pressure should be maintained between the fuel pump (by a built-in one-way valve) and the FPR's.

    P.P.S. Just seen that Dragon has already said that.....
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  13. #13
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    Happy memorial day! Was at the lake all weekend. Going to the Carlisle Ford Nationals in PA this week...

    Anyways, I'll have to check for the pressure bleeding off so fast. Its not the FPRs so it must be at the pump housing. The fuel filters I have not personally replaced. They have been replaced before.

    The ID sensors are brand new. Doesn't mean they aren't bad, but they came on a new set of plug wires. I'll get my scope out and see what output I'm getting from those. Anyone know what to look for?

    I don't believe there are any codes. I haven't had the chance to try to get that all working again. I've been very busy.

    Does anyone else think the EML should be replaced or should I wait to do that?

  14. #14
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    I'm back! I've been traveling to DC for work a few times the past few weeks and just been busy overall.

    I finally pulled the EML tonight and ordered an exact replacement. $45 on eBay, not bad. Will replace and cross fingers it changes something. If it doesn't.... I may have to sell it. I can't sit on this thing much longer. That would be really sad. I'm so close it feels!!! I honestly don't think this is the problem.

    I'm going to check the ID sensors with a scope this week. They're brand new but new things can be bad.

    Just a recap: the engine will fire up but the injectors stop firing a few seconds after startup and it turns right back off. If anyone has any more suggestions please feel free to tell me.

    I have air, spark, and fuel pressure is ~50 PSI although very jumpy.

    I've replaced:
    - Both fuel pumps
    - Pieces of fuel pump hose
    - Both crank sensors
    - Plugs and wires/ID sensors
    - FPRs

    Something really weird. When I first got it and had just replaced the fuel pumps, I got it to run on 1 bank for about 10 seconds before it died. Now it won't run for more then 3... Just odd...
    Last edited by breeves002; 07-03-2016 at 03:15 AM.

  15. #15
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    So how about fuel pump relays??

  16. #16
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    Disco II 850i MERs 750il
    One problem I had was shorting of the fuel pump relays to the fuel pump relay fuses wiring that goes along the firewall. The insulation had crumbled and the bare wires shorted.

  17. #17
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    I have fuel pressure and the fuel pumps run, so how would the relays be a problem? Its the injectors that turn off - the pressure is solid.

    I'm being told that if you unplug the coolant temp sensor the DME's think the car is super cold and will fire the injectors in batch firing mode instead of sequential. He also said it should run for a little while with the ID sensors unplugged.

    Can someone just try unplugging their ID sensors and seeing if the car runs more then 3 seconds?
    Last edited by breeves002; 07-03-2016 at 01:27 PM.

  18. #18
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    Turn the ignition on without cranking the car over, Under the hood, Do you get a Buzzing sound from your Throttle bodies/DK's?

  19. #19
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    Yes buzzing is there. The throttles operate with the car in the on position. They both open if I push the gas pedal.

  20. #20
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    That means your hidden fuse is not the issue, Strike one! If you don't wanna throw parts at it, Get or borrow a diagnostic tool, What type of plugs did you install and check the condition of the caps and rotors.

  21. #21
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    Spark is fine. Like I have said previously, the problem is the injectors are turned off. I used not the OEM ones that are impossible to find but the newer Bosch ones. I didn't look at the caps and rotors - I should, but that won't make it die right away. The issue is the car starts, then turns off due to the computer cutting fuel... 3 seconds later.

  22. #22
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    I'm dealing with this as well, however only one bank is doing this. Did you fix yours?

  23. #23
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    Did anyone get this solved?

    Quote Originally Posted by Cup1d View Post
    I'm dealing with this as well, however only one bank is doing this. Did you fix yours?
    How about some follow-up on this problem?

    Thanks

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