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Thread: The Undiagnosable E30

  1. #1
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    The Undiagnosable E30

    Undiagnosable may be a bit of an exaggeration, but not by much.


    • Car: 1986 BMW 325e (Manual, Delphin Metallic Sedan)
    • Problem: Intermittent no start


    Due to extensive troubleshooting, I'm going to try and keep this as brief as I can and focus on what we think is the issue. I apologize if this gets wordy and thanks in advance for any advice I may receive. I've had this car for almost a year now and my frustration has brought me here.

    In the beginning the car would not start on occasion and would require several attempts or just waiting a day or two and trying again. When it would start, it ran like a champ. Then over the course of 6 months or so, it got to the point where it practically wouldn't start at all. When this occurred, I wouldn't get spark or fuel, so the CPS seemed to be the only logical culprit.

    I replaced the CPS and speed sensor on the transmission (ETA engine) and made sure the pin on the flywheel was present and not dirty, broken, obstructed, etc. Although the plastic connectors had become brittle from thousands of heat cycles in the engine bay and had practically disintegrated. I found replacement connectors, but couldn't track down the pins, so I just hard wired on some generic connectors. I didn't realize it at the time, but this reduced the resistance to a level that the car would start but run extremely rich. Unfortunately the Bentley manual gives two values that the CPS could be, which added to the confusion. So I said screw it and took it to a local BMW mechanic that specializes in old Bimmers.

    This mechanic determined my connectors to be the issue, put in new sensors with factory connectors and soldered on factory connectors to the harness side. I went to pick up the car and at that time, the car would start regularly for the next month or so (although the idle was rougher than normal). But then it began to play its games again, going from occasionally not starting to where it's at now, not starting 98% of the time.

    We believe that soldering the connectors onto the factor harness could be the issue, but the resistance is coming back within the correct specifications at 1.031 k Ohms (Specs: 960 +/- 96 Ohms). If I could find an ETA harness I could swap it out and say for sure, but those are not easy to find, short of buying another entire car. My initial thought was to pull the harness and rebuild it, but these sensor cables have a bare stranded wire that wraps around the two main wires, in effect, shielding them. Which I have a feeling is playing into this issue, but my electrical knowledge isn't as thorough as I thought.

    So, based on all that gibberish above, what are your collective thoughts? Keep in mind, I'm still not 100% sure the wiring is the problem, although I've replaced the DME and nearly everything else, so I'm at a loss what else it could be. I've left out a ton for the sake of brevity, feel free to ask any questions you may need and thanks again for taking the time to read any of this.

  2. #2
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    Is your key switch on the column good?

    - - - Updated - - -

    It could be worn

  3. #3
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    Good question, that's one of the few items I haven't checked.

    If the engine cranks, but won't start and fuel isn't being delivered at the time of the problem, wouldn't that rule out the ignition switch though?

  4. #4
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    I had the same exact car at one point and I know that the DME itself had been replaced by a BMW mechanic, Which I thought to be somewhat noteworthy because I always thought the electronics on these cars were pretty reliable. It might be worth your time to swap the deer me with a good known used one and see if thatís not the issue itself

  5. #5
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    You can find eta harnesses on ebay almost all the time, if you still want to try that out

  6. #6
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    Isnít there some kind of disabling feature thatís built into the cars OBC that could be causing the issue?
    https://www.bimmerforums.com/forum/showthread.php?2159502-1992-E30-won-t-start-after-changing-OBC-!!-HELP-!!&highlight=E30+OBC+disable
    Last edited by msservices; 07-26-2020 at 09:26 AM.

  7. #7
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    Quote Originally Posted by msservices View Post
    Isn’t there some kind of disabling feature that’s built into the cars OBC that could be causing the issue?
    https://www.bimmerforums.com/forum/s...30+OBC+disable
    I suppose that is a possibility. It's a double relay that is triggered by the OBC. It's under the dash. The start disable function works by interrupting power to the DME pin 27 start input. The relay is normally closed, but the OBC will pull it open when the CODE function is active. To bypass it, remove the relay component and jumper green to green/red. Everything else can remain disconnected.
    "Howdy, Folks!"

    1986 Delphin 528e - Has led a hard life, 290k and still alive.
    1989 Zinnoberrot 325iX Sedan - My winter snowmobile. (Deceased)
    1998 Avus Blau 328iC - My topless summer girl.
    1999 Audi A4 Avant Quattro - Crap can, but I'm in too deep.
    2012 X3 xDrive35i - My new snowmobile.

  8. #8
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    Long shot, check the engine grounds, the big one under the alternator and the smaller one on the valve cover. The large one tends to corrode and / or get loose. While you're at it, check the one off the battery. Poor grounding can cause flaky problems.
    2004 525i Sport, Manual - 1985 325E Coupe Manual

  9. #9
    richardodn's Avatar
    richardodn is online now Old Guy BMW CCA Member
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    The big ground is the only one that matters. The valve cover ground is for radio noise suppression.
    "Howdy, Folks!"

    1986 Delphin 528e - Has led a hard life, 290k and still alive.
    1989 Zinnoberrot 325iX Sedan - My winter snowmobile. (Deceased)
    1998 Avus Blau 328iC - My topless summer girl.
    1999 Audi A4 Avant Quattro - Crap can, but I'm in too deep.
    2012 X3 xDrive35i - My new snowmobile.

  10. #10
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    Interestingly, the car has consistently started ever since I mentioned it's name in public. So I'll have to wait until it decides to do it's thing again before performing additional troubleshooting steps.

    Thanks superj for mentioning that eBay has harnesses. For some reason I didn't even think to check there... and you're right, there's a couple for sale at this very moment. I might end up going that route, we'll see.

    And I have read about the OBC immobilizer and went down that path, eventually jumping the green / green red wires with no noted change.

    Regarding the grounds, I have looked into some, but not all. When I got the car, the valve cover ground wasn't attached at all and I thought that was odd that the car even worked. But now knowing that it was just a radio interference ground, that makes more sense. I'll look into the alternator grounds when I get a chance.

    Thanks again everyone for their thoughts on this, I appreciate all the ideas and information.

  11. #11
    richardodn's Avatar
    richardodn is online now Old Guy BMW CCA Member
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    The alternator ground is only found on cars where the alternator is isolated with rubber bushings. Most alternators ground through the brackets, through the engine, and through the main ground strap to the chassis.
    "Howdy, Folks!"

    1986 Delphin 528e - Has led a hard life, 290k and still alive.
    1989 Zinnoberrot 325iX Sedan - My winter snowmobile. (Deceased)
    1998 Avus Blau 328iC - My topless summer girl.
    1999 Audi A4 Avant Quattro - Crap can, but I'm in too deep.
    2012 X3 xDrive35i - My new snowmobile.

  12. #12
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    If the starter is engaging, isnít that an indication that the motor is in fact grounded?

  13. #13
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    It was only a matter of time.

    So the car started consistently for about 4 or 5 days in a row and then today... crank but no start. I've looked into the alternator grounds and they're clean and secure. I tickled the sensor wiring, since this seemed to work once or twice, but again, just an unfortunate coincidence I'm sure. And no help today. I'm also sure that it'll start eventually, later this week without a single change being made. Possibly the most frustrating issue I've encountered. First car I've owned that I was unable to figure out and even the mechanic is left scratching his head.

  14. #14
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    And now the car started again on the first turn of the key. The only thing that changed from last night when I tried over 100 times to get it to start and today, is the passage of time. I drove to get gas and when I returned it would restart without an issue.

    This is why I don't think it's the harness and is keeping me from buying another. I can't just continue to throw parts at it without a valid reason to. Hell, at one point I was convinced it was the fuel system and replaced every component in it.

    So the question remains... what would cause a BMW E30 to mysteriously start / not start for seemingly no reason at all?

  15. #15
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    Mine would do that when the engine harness connector had a bad connection. This is the big round connector close to the firewall on the drivers side. Open it up and look at all the connections.

  16. #16
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    The C101 connector? Yep, been in there too. I guess it's possible that there's corrosion I haven't seen, I'll have to dig into it more thoroughly I guess.

  17. #17
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    On the recent times it has failed to start have you confirmed there is still a lack of spark and fuel?

  18. #18
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    Lack of fuel, yes. It's an easy thing to check by disconnecting my cold start valve fuel line, so I usually do so. Lack of spark, no. That takes a little more work, and since I've confirmed it several times before, I usually don't perform that step.

  19. #19
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    Alrighty, today was different. Actually the last few days have been different. Instead of the car not starting 98% of the time, it's closer to 50%. But that's not what I'm here to explain.

    For the first time in my presence, the car started, but died while driving. Just shut right off like I took the key out. It's never done that. If I was able to get it to start, I could drive hours without issue.

    I was on a hill so I tried to bump start without any luck, so I parked it and began to troubleshoot. No fuel, check. Fiddled with CPS wires, check. Nothing. Then about 10 minutes later, she fired up. But here's where it's different. Any time the engine rev'd to about 2000 rpm, the car would lose power, backfire and stop accelerating. In every gear. The idle was also much higher, I believe it was about 1,200 or so instead of the 750 or so it usually idled at. And it was clearly running rich.

    Now I've experienced this before, but it was right after I put on the aftermarket connectors. But back then, I couldn't even drive the car. This time I was able to drive it the 20 miles or so back home as long as I shifted before I got to 2k rpm. It was an interested experience.

    So I waited until it got a little cooler outside and was about to tear into the wiring to make certain the were no breaks or poor connections, when it fired right up and no longer had any issues with idle, running rich or breaking up at 2k. I drove it around the block and even did a donut or two and it acted fine.

    As confused as I am, I can't imagine this problem could be anything other than the wiring between the CPS and the factory wiring harness. My neighbor is convinced that it's the wiring, saying he's had a similar issue with his Jeep.

    So what do you think? Buy an old crusty 325e wiring harness on eBay for $200 to $250. Or try to rewire the entire section as close to factory as possible? Or just do an engine swap and call it a day. To be honest, I bought a 1988 325i automatic that the trans has went out on just to steal the engine and do a stroker build. But I don't have the funds to make that happen today.

  20. #20
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    That particular car would have two fuel pumps, one in the tank and one in line, Iím suspecting one of them is working intermittently, which could also be wiring/relay related, or a pump crapping out. At this point I would connect a fuel pressure gauge near the engine and drive the car until this happens again, and hopefully your fuel pressure is minimal when the car dies/ starts acting up again. If it does end up being the pumps themselves you could convert it to a single in tank pump using your newer parts car

  21. #21
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    Man, this site does not like me. Every time I've tried to edit a post, it deletes it. That's just as frustrating as my car's issues.

    So here's what I originally wrote...

    Thanks for the insight msservices. However I've replaced every component in the fuel system as I too thought that was the problem at one point. New relay, new in tank fuel sender, new frame mounted fuel pump, new fuel filter, new fuel pressure regulator, rebuilt injectors. The fuel system has been completely rebuilt and pressure tested and I just can't see it being part of the problem now.

  22. #22
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    New in tank sender? Or new in tank sender and pump? Just clarifying that I meant that your car Specifically has two pumps, one to transfer and one the create the high pressure, as opposed to later models which use the one in the tank to do it all. Either way you would still need to rely on a fuel pressure gauge even if you replaced everything you possibly thought you could replace.

  23. #23
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    My 87 vert was not starting. I replaced both fuel pumps and did well for a time then had intermittent starting but not turning over which required a new starter. some similarities but you seemed to have covered all the same bases. Good luck. let us know when you find the Gremlin.

  24. #24
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    Ok, my results aren't currently proven, but I feel I've reached a milestone and wanted to share my findings.

    A week or two ago the car got to the point where it just wouldn't start anymore. Maybe once or twice out of hundreds of tries. And when it would start, it would die a couple minutes later.

    Fast forward to this weekend. I really dug into the wiring in the engine compartment. Checking relays, fuses, re-soldering connections, cleaning connections, no-ox on connectors, etc. Frustratingly, no change.

    Then I began working on items in the cabin. Removing and re-inspecting the DME, OBC, wiring that connected different components in the dash, etc. Again, no change. The car refused to start.

    This morning I continued researching and reading forum posts and looking into anything that could help me find a solution. Which led me to the OBC immobiliser rabbit hole. Oh, there's a OBC relay and computer under the driver's dash as well?

    So, long story short (too late), it appears that a wire the plugs into the OBC box under the dash, may have been loose. After re-seating all the wiring, guess what?

    Now it's only been a couple hours since I made this revelation, but so far, the car can be turned on and off and driven without issue.

  25. #25
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    Hopefully that's it

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