Misfire - Crank sensor?

Ok, I'm re-visiting this one. After having new tyres, lower front arms and a brake accumulator fitted, finally excorcising a few gremlins, I really need to face the misfire issue I still have after what must be over 2 years now.
I am 90% sure it is not a cylinder that is down as the misfire doesn't seem confined to just one. If I disconnect each coil pack in turn, the engine runs rougher on all 8 cylinders hence my theory it's something to do with the ignition control or fuelling rather than a coil pack or injector.
If the car is plugged in, there is a stored fault of crank sensor which has been replaced. The fault then stays away when cleared until the engine is revved to about 4000rpm then the engine management light flicks on and the power dies for a second until rev drop, that is when the fault for crank sensor shows back up.

I have shone a torch on my front crank pulley while the engine is running (where the sensor reads the signal from) and I can see quite clearly it doesn't run 100% true so my theory is due to the uneven wobble of the pulley, once the revs reach so high the crank sensor can no longer read the teeth on the wheel and the engine cuts the power for a second until it manages to read the teeth again. I know replacing the pulley would more than likely cure the engine not revving high but could this also be the source of my engine misfire, even at idle? Can a worn front crank pulley cause the signal to have the odd 'blip' i.e. miss a tooth and cause a small misfire?

I'm really hoping that I may finally put this one to bed, my worry is that if it doesn't it may end up costing me much more money to get it into a specialist

The pulley is has a rubber donut around the centre and once this wears it can then cause the outer toothed ring to resonate meaning it doesn't run true. My theory was that if this isn't always running as close to the crank sensor as it should then the ECU cannot get a proper signal causing possible misfire and the revving issue.
I was sure it is the cause of my engine not finding it's way past 4000RPM but that problem, again seems to have cured itself (that's the issue I thought had been cured by sorting the plug out but it returned a short time later) The part from BMW is over £300 but I have seen a guy on ebay selling them for most models for about £100 so for that price it's worth a roll of the dice.
Perhaps I'll bite the bullet and just do it, that would eliminate another possible cause anyway.

Mike

Yes, was a genuine sensor fitted and it made no difference at all.

Mike

Welcome to the forum Andy

What are your coils like?

Could really be anything from any one of the sensors to a duff coil.  A diagnostic check is probably your best bet.

Andrew

Hi Andrew,

Thanks for the message and info, all coils ok and diagnostics done and clear, car is going well now,

cheers,

Andy

bulletproofbomb wrote: How strange- I had a funny feeling to check this forum today (after forgetting about it what with one thing and another) and my name is mentioned!  As you JSW2000, perhaps it is a resonance at higher speeds, though I think the gap is meant to be about 1mm max, so I'd expect to see some signs of impact if it is wobbling enough to affect things. I'll refresh myself on this topic later, as have to dash just now, but I can't believe it is still misbehaving.... My e34 530i has just decided to stop starting after a period of iffy starting when hot, so I think I'll need to buy a new Crank Position Sensor, and hope I have a smoother ride....

that's what we call "hunch", or suffice it to say you have a bond with this forum.