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Thread: Ignition issue

  1. #1
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    Ignition issue

    After a long period off the road after an ignition lead failure I finally got all the parts required to get my 91 850i up and running again. Replaced leads and rotor on the side that the lead failed on.

    No longer losing a cylinder (it was cyl 12 lead with the sensor that was faulty) but the car now seems to have a harmonic rumble as if one or two cylinders are not firing. I've tested the spark to all cylinders successfully but spark does feel a bit weak on the LHS that had the issue.

    Not tested compression or plugs so can't identify faulty cylinde/s. MAFs are new and I've tried back ups. Leads are good. Could a weak coil cause this?

    If it's firing okay would this symptom be consistent with DKs that need re-syncing. Unfortunately can't scan the car currently due to one or more faulty modules that I've yet to ID.
    Last edited by jeffbebe; 04-21-2017 at 12:25 AM.

  2. #2
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    I have no actual experience on an 850i,so can only give you a general recommendation.
    (850's are a beautiful car btw, I remember admiring them when they were first introduced.)
    I would replace the sparkplugs(only NGK).
    Question, how does it feel a bit weak on the LHS? How did you tell, isolate that?
    If one lead(ignition wire) failed due to age, I'm assuming that the rest are in the same deteriorated condition,
    So replacement as set would be recommended. Here is an old school test for wired sparkplug ignition systems:
    Pick the darkest nighttime location(garage,driveway),open hood, start engine, peer into the location of engine,
    Do you see dancing flashes of light emanating from any ignition wires? If so, replace.
    A further test for failure of sparkplug wires is applying a fine water mist with a spray bottle to the wires,
    The dancing sparks confirm their deterioration, that was hidden in less humid conditions.
    Also how long was she off the road?
    Old fuel may cause random misfires.
    Scan for codes as soon as you are able to, they provide clues to follow for repairs.
    "Choosing the correct shop is as important as the correct diagnosis

    Former owner of a Red RL411 wannabe owner of pictured vehicle

  3. #3
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    Sorry, I probably should have been clear. I replaced the complete lead set on both sides. NGK plugs are great but I understand don't work brilliantly without also upgrading the coil packs which I haven't done (yet).

    I am best-guessing at weak spark on the LHS after trying a pretty old school test (since I can't scan currently). I loosened all the plugs on the distributor cap while the engine was off. Then started the engine and one by one removed the plugs with a pair of plastic tongs. I would normally expect some pretty loud clicking or even to see the spark jumping but the spark just didn't seem that strong on that side. Unplugging any of them didn't seem to make much difference to idle but I guess it's harder to detect with 12 cylinders! Distributor cap was new but rotor is old (it looked okay but I guess it could be at fault).

    I really need to isolate the faulty cylinder first, I think. So will initially run compression tests. If they all check out I'll try the spark test again but this time disconnect one bank so that any changes (or not) when I disconnect a plug are obvious.

    If compression and spark checks out then I guess I'm at a loss.

    I've never had DKs that aren't synced so don't know what that feels like. Is it possible since the batteries were unhooked for some time?

    Incidentally, I double checked the firing order when fitting the new leads but I'm going to triple check!!!
    Last edited by jeffbebe; 04-21-2017 at 04:01 AM.

  4. #4
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    A scan with BMW software like INPA would be helpful.
    Are the sparkplugs new, just not NGK?
    Battery disconnection cleared adaptations,hence the rough running,
    Here is what I found concerning DK synchronization:http://www.bimmerfest.com/forums/sho...58&postcount=9
    Correct firing order is essential, I would check.
    "Choosing the correct shop is as important as the correct diagnosis

    Former owner of a Red RL411 wannabe owner of pictured vehicle

  5. #5
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    I would check the firing order again - sounds like two cylinders are swapped - details here:





    http://www.meeknet.co.uk/E32/V12_Distributor_Leads.htm
    Last edited by Timm; 04-21-2017 at 05:50 AM.
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  6. #6
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    Quote Originally Posted by jeffbebe View Post
    ... I replaced the complete lead set on both sides. NGK plugs are great but I understand don't work brilliantly without also upgrading the coil packs which I haven't done (yet).
    You've got that backwards... NGK low resistance plugs are the ONLY ones you want to use with stock coils... with the blaster coils, you can run anything you want.
    Bosch plugs are NOT the ones you want with stock coils.

    ... the NGK plugs are BKR6EK. Use those.
    Last edited by cartoonz; 04-21-2017 at 07:15 AM.

  7. #7
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    Quote Originally Posted by Timm View Post
    I would check the firing order again - sounds like two cylinders are swapped - details here:





    http://www.meeknet.co.uk/E32/V12_Distributor_Leads.htm
    Thanks Tim. I'll check again. Always possible I had a brain fade.

    Quote Originally Posted by cartoonz View Post
    You've got that backwards... NGK low resistance plugs are the ONLY ones you want to use with stock coils... with the blaster coils, you can run anything you want.
    Bosch plugs are NOT the ones you want with stock coils.

    ... the NGK plugs are BKR6EK. Use those.
    Thanks, I always thought it was the opposite!!

    Quote Originally Posted by MIKYZZ4 View Post
    A scan with BMW software like INPA would be helpful.
    Are the sparkplugs new, just not NGK?
    Battery disconnection cleared adaptations,hence the rough running,
    Here is what I found concerning DK synchronization:http://www.bimmerfest.com/forums/sho...58&postcount=9
    Correct firing order is essential, I would check.
    Newish plugs. I have INPA but can't currently scan due to some other issue, probably a faulty module.

  8. #8
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    Seriously, put in the correct plugs before you beat your head against the wall... this has been the cause of these same symptoms countless times.
    If nothing else, then at least you have the security in knowing the plugs are correct and not the problem... but trying to troubleshoot without is just foolish.

  9. #9
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    Current plugs are Bosch F8LCRs with about 4-5000kms on them. Had no problems with them prior to the cyl 12 lead failing but will certainly consider replacing, though I'd prefer to determine cause before spending money.
    Last edited by jeffbebe; 04-21-2017 at 10:24 AM.

  10. #10
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    Quote Originally Posted by jeffbebe View Post
    Current plugs are Bosch F8LCRs with about 4-5000kms on them. Had no problems with them prior to the cyl 12 lead failing but will certainly consider replacing, though I'd prefer to determine cause before spending money.
    And that's the root of the problem with the Bosch plugs.
    I can't even count how many threads just like this have been resolved by using the correct 1K plugs - which are the NGK's. And yeah, everybody tries to argue the Bosch plugs are "supposed to be" the correct plugs... they are not.
    No idea how you are going to determine the root cause while ignoring the elephant under the hood....

  11. #11
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    I'm certainly not arguing for Bosch. I just went with a recommendation at the time and tracked down a new set of the discontinued F8LCRs. The car had NGKs when I bought it and was running very rough. They were probably just the wrong ones. Previous owner was not an enthusiast.

    Will certainly look at replacing with 1K NGKs. Are BKR6EK the correct plugs?

  12. #12
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    Yup.

  13. #13
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    Replaced the plugs with NGKs and checked firing order on both sides but issue persists. It's like a thudding sound in the engine as if a cylinder or two is not firing at all.

    Only a slight falter if I unplug RHS MAF whereas LHS almost stalls without MAF. Have tried swapping MAFs but nothing changes.

    Guess I need to check cylinder by cylinder to determine which one/s is faulty.

    Any other suggestions or obvious things I've missed!

  14. #14
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    So, its not the MAF's since nothing changed! Also most likely, its not the ignition either since nothing changed unless the RHS ignition coil has some kind of error or lose connectors (1,15). Try swapping them and hope for a difference. What I believe is an error in the fuel supply! Disconnecting the control cable from a fuel injector has the same effect as disconnecting an ignition plug with the difference that the ignition plug will remain dry since there will be no fuel into the cylinder. Try to find out which cylinder is not working fully out, it sounds by your description that some cylinder is working with too little or maybe no fuel injected in it. Then check the fuel injector for that cylinder, you could have got some dirt in it giving you too little fuel or nothing. Also check the RHS fuel pressure, the fuel injectors are sensitive to the pressure over the injectors it shall be about 3-3.5 bars. The pressure is regulated by the pressure regulators in the front of the fuel rails and also the pressure supplied by the fuel pumps (about 6 bar).

  15. #15
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    physically swap the coils and see if the miss changes sides

  16. #16
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    Problem is, I can't tell which side the miss is on now!

  17. #17
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    Quote Originally Posted by peake View Post
    So, its not the MAF's since nothing changed! Also most likely, its not the ignition either since nothing changed unless the RHS ignition coil has some kind of error or lose connectors (1,15). Try swapping them and hope for a difference. What I believe is an error in the fuel supply! Disconnecting the control cable from a fuel injector has the same effect as disconnecting an ignition plug with the difference that the ignition plug will remain dry since there will be no fuel into the cylinder. Try to find out which cylinder is not working fully out, it sounds by your description that some cylinder is working with too little or maybe no fuel injected in it. Then check the fuel injector for that cylinder, you could have got some dirt in it giving you too little fuel or nothing. Also check the RHS fuel pressure, the fuel injectors are sensitive to the pressure over the injectors it shall be about 3-3.5 bars. The pressure is regulated by the pressure regulators in the front of the fuel rails and also the pressure supplied by the fuel pumps (about 6 bar).
    Seems to be a lot of unburnt fuel so I'm picking a spark or compression issue rather than a fuel system problem but will check the fuel supply when I confirm which cylinder/s are not working.

    Feels most like incorrect firing order as Tim suggested but I've checked and checked again and everything is correct. Can anyone tell me what unsync'd DK motors feel like? Car has been dormant for six months with the batteries unhooked waiting for parts. Is it possible she just needs a decent long drive? I've been cautious of driving her for long when things don't feel right.

    Again, advice appreciated. Thanks

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