My 87 635CSi begun acting strangely about a month ago - one day it took several tries to start it, it just cranked and cranked without even firing, finally after a total of 20 seconds of cranking (in a few cranking spurts) it started. Then, the day before Christmas eve (christmas eve eve), it wouldn't start at all. I drove another car that night, and the next day it started up just fine. No problems, until last night it again refused to start. It still won't start this afternoon.

I figure the fuel pump is a good first place to start looking, but I've had cars do the same thing with ignition problems. Since this is my first BMW, I'm somewhat unfamiliar with their electronics, specifically in the engine bay.

The fuel pump is a good place to check out. You might also check the coil. Mine was playing the same type games and I came to find that the coil was shorting to a side post. I eventually found that the main coil wire was burnt through (and the car still ran). I was able to butt the ends together in order to get to the parts house and replace it (two days later).

Usually if you get a clogged fuel pump, you're not going to run. It doesn't tend to be intermittant.

Good luck.

since it only happens when its balls ass cold outside, I thought maybe my fuel lines were freezing, so yesterday I put some fuel line antifreeze in the tank. It hasn't got below 40 yet, but I think on saturday morning its supposed to hit 7F, so we'll see what happens.