Re: Jekyll and Hyde driveabilty - or am I nuts? (archive)

Well, what I think is happening is it is just too lean during warmup. When O2 sensor kicks in, it adjusts mixture. If engine is partially warm, the mixture is gets is rich enough. But I also feel like it runs too lean sometimes when warm, hence the slight feeling of laboring/sluggishness under load. Haven't checked the coil other than resistance, which is fine. I am starting to really feel like it is a fuel supply problem of some kind, either pumps/filter or injectors. So should probably get fuel pressures tested (or buy a guage and do it myself). jumped the transfer pump today and checked current draw, it was only .57 amps at 11.5 volts, so that should be fine.

I do see what you're getting at with the resistor. Mechanic told me he once rigged a varible resistor attached to the coolant sensor, so he could add variable amounts of resistance, until the notorius cold driveability issues of the late 80s 7 series were fixed. Then he'd solder the proper value in there. There was a tsb on adding resistors in some of these cars...

Todd:

Have you checked the ignition coil? A friend of mine reported stumbling acceleration on his 91 E34 M5 and it turned out to be the ignition coil. All tests checked out, but it was bad somehow.

Not sure why it all becomes OK when the car is warm. Perhaps the coolant temp sensor leans out the mixture as the engine warms and the leaner mixture is easier to ignite? I have little experience with this sort of problem so that is the best guess I can come up with.

One way to do this would be to measure the resistance of the coolant sensor when it is hot and putting an equivalent resistance into the circuit, removing the coolant temp sensor, and then running the car from cold.

Neil Deshpande
http://www.neilwerke.com

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I've had a cold driveabilty issue for a while, (88 M5 w/ 82k) drives like crap (hesitates, lurches, occasional backfire) when stone cold, then runs fine when O2 sensor kicks in.

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