Sudden Death

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Hefeweizen
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Sudden Death

Post by Hefeweizen »

So my son is driving down the road in his 6er when she, all of a sudden decided to die. We have a spark from the coil to the distributor cap (dizzy cap) but there is nothing coming out of the cap. Rotor is turning and the engine has a good ground. Anyone ever had an experience like this? We swapped all parts we suspected from his 6er to mine and my 6er started every time :-k
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hornhospital
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Re: Sudden Death

Post by hornhospital »

The rotor is firing to ground through the center post.
Ken Kanne
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Re: Sudden Death

Post by Hefeweizen »

hornhospital wrote: Tue Mar 06, 2018 3:43 am The rotor is firing to ground through the center post.
Thanks, can you elaborate please?
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Brucey
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Re: Sudden Death

Post by Brucey »

the rotor arm is mounted on an adaptor that is bolted to the nose of the camshaft. I suppose that it is possible that this adaptor has worked loose.

BTW the system firing voltage varies with the plug gap, the compression ratio and one or two other things. If these are different on one car to the other (or you have just cleaned the rotor/cap of damp) then it is possible for one engine to run nicely and the other not with the same parts.

The acid test is driving the car on part throttle once it is warmed up; dodgy HT parts will usually manifest themselves under these conditions.

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Re: Sudden Death

Post by Hefeweizen »

Thanks Brucey! Would the possible lose part be #5 or #7 in the diagram?
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Rainer
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Brucey
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Re: Sudden Death

Post by Brucey »

part 5 is the one, held on with bolt 3.

Although on reflection I find it hard to believe that it could have moved far enough to cause (say) a cross-firing or no firing problem.

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Re: Sudden Death

Post by 603racing »

If something is loose, my guess would be #3 backed out again causing #5 to not spin. I think there is also a keyed pin (maybe #6) that keeps #5 in proper position.

Did you swap the coil and coil wire? I've seen bad coils deliver spark to the rotor but not enough to make the plugs fire.
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Hefeweizen
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Re: Sudden Death

Post by Hefeweizen »

Thanks,

will check on that. We did check if the rotor was turning and that was the case. #5 may not turn the distributor cap is on? Have to check on the tightness there. Thank you!
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Re: Sudden Death

Post by hornhospital »

Speaking from experience with my 633, the rotor failed by developing a carbon trace right through the arm directly to the tee piece (#5). I have never seen one do that before or since. It was a genuine BMW part, possibly the original to the car. I can only think it was a manufacturing defect that had a void in the resin that took years to develop the trace to ground. When I changed the rotor as part of the diagnostic process, the engine ran again. It was only after close examination that I realized why the arm was the culprit.
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Re: Sudden Death

Post by Hefeweizen »

So we checked #5 and that piece is on tight. Asked my son if he checked for ground on #5 and he did not check yet.
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Re: Sudden Death

Post by Brucey »

from the symptoms reported it is quite likely that either the rotor or the cap is firing to ground. That it doesn't happen in another car could be because the firing voltage is different.

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Re: Sudden Death

Post by Hefeweizen »

Brucey wrote: Thu Mar 08, 2018 7:13 am from the symptoms reported it is quite likely that either the rotor or the cap is firing to ground. That it doesn't happen in another car could be because the firing voltage is different.

cheers
Brucey,

thanks! Have to admit that I really never heard of this firing to ground. Is there a remedy?
Last edited by Hefeweizen on Fri Mar 09, 2018 12:12 pm, edited 1 time in total.
Rainer
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"If you think a good European mechanic is expensive, try a bad one!"
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Re: Sudden Death

Post by Brucey »

normally (as others have suggested) the parts are jiggered and can only be replaced. You may or may not see a pinhole through the insulation or a track on the surface.

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Re: Sudden Death

Post by Hefeweizen »

Some time in the near future, I will hand my 6er over to my son so he can take my working parts and put them into his car.
Rainer
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"If you think a good European mechanic is expensive, try a bad one!"
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Re: Sudden Death

Post by Hefeweizen »

Good ending! He had a lose connection at his flywheel position sensor :roll:
Rainer
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85 635CSi (RIP 3 May 19)
80 633CSi (Red Euro, Project)

"If you think a good European mechanic is expensive, try a bad one!"
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