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Re: The story (long) (archive)

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Posted by Neil Deshpande on October 23, 2001 at 23:17:50:

In Reply to: The story (long) posted by ///M5AD on October 22, 2001 at 13:57:47:


The crank position sensor in intermittent operation would cause the symptoms you describe. There is no knock sensor on this car.

The inductive pickup switches from parallel to sequential injection, saving about 1.5% in fuel economy from what I've read in _general_ literature. Instead of 50% of the fuel required at each cylinder spraying every 180 deg of crank simultaneously for all cyls, the sequential sprays it just before the valve open to accept it. That or something similar. It only improves fuel economy. Nothing else. I broke mine when I rebuilt the top-end and have yet to spring for a new one at $90.

The missing engine has dumped raw fuel into the exhaust and catalyst, poisoning or melting the latter. Running rich or dumping fuel into the engine cools the engine and heats the exhaust. The rotten eggs smell (sulphonated hydrogen or hydrogen sulphide) is a signature of a failed cat. A new catalyst will be required to pass emissions. Once you repair the car run for about 3 weeks to see if this blows out the cat. If the smell is still there, replace.

What pickup did you repair? Crank sensor intermittent or sequential injection? The latter should do nothing. The former, when OK, will cause the engine to run right. However, it is possible (and I have no experience here) that your solder has introduced some resistance somewhere that is confusing the ECU. Shaky at best this theory. I am not aware of any learning in the S38 ECU. I think that is an OBD-II thing.

Plus wires are not a maintenance item on the car as far as I know, but anything is possible. I have not measured the operating voltage of my car's ignition system.

There are no technical manuals that I know of. Refer to for information.

It would be prudent to seek a second opinion from a person with a reputation as I'm merely an interested home mechanic with some wise friends, which is far from being a master tech though I've met more than one dumb master tech. I would recommend and its owner Brett Anderson for this purpose. He has a pay-per-incident service and is the best tech I know. Writes for the Roundel and all that. Helped with my top-end rebuild.

Neil Deshpande


We had trouble with the car (91 M5) during a road trip vacation on the west coast of BC. 1000km from home and no dealer within an hour's drive, it just died. I could re-start it but it died shortly afterward.

Had it towed to a franchised Mercedes dealer (the only high end dealer in town) and after 4 hours of diagnostics the mechanic found the problem was the center terminal in the crank position sensor connector (behind the cover in the first picture) was pushed back and making intermittent contact, breaking when heated. He said it was a knock sensor but I didn't argue with him.

He also noted the inductive sensor on the #6 ignition cable was broken, its housing was shattered and both fine wires broken. He said that pick-up was only for cruise control and wouldn't affect the way the engine ran.

Trusting the car was OK, we made the 1000km return trip to Calgary with the engine missing and burbling all the way. I was expecting it to crap out at any moment - not the most relaxing drive considering there are times when you are over an hour from civilization and have no cellphone connection...

I repaired the ignition pick-up this morning and the car is running a lot better but still not perfect. Do you suppose the ECU is facing a learning curve after the return of the signal from the #6 plug? After a 25km drive this morning, I had a slight "rotten egg" smell from the exhaust - better than it was before the repair. There had been a terrible off idle stumble which is now gone.

Do you think I'm facing other problems after driving so far with that pick-up broken? Cats? The check engine light never came on and when I do the "stomp" test, all I get is short flash and then long flash repeating endlessly.

The mechanic also said that my ignition is running at about 17kV rather than the 10kV it should be, indicating a need for new plug wires - opinion?

Finally, do you know of a source for service information for the M5? The wiring diagrams in the Bentley book have occaisional references to M5 but is mostly useless. The dealer is mum on the subject. When will BMW get with the program and publish tecnical manuals??

Thanks for your help.
Anthony Doyle


There are three connectors there:

1. Air pump clutch signal - not really a sensor.
2. Crank position sensor.
3. Impulse generator for sequential injection.

Neil Deshpande


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