Spark randomly hiccups..

[Wingnut]

88 325I

Happens at low RPM, and idle. when at idle, car dies then comes back quickly. When moving, car jerks like an SOB. Sometimes, the car won't start. (this is how i found out there was no spark) then, randomly, it will start.

I've
replaced crank position sensor
replaced Main relay
swapped ECU with known good
cleaned and tightened all major grounds

next is
coil and coil wire to cap.
cap and rotor

Anyone have any other ideas?

[Komzorz]

I've had a cap and rotor do that to me, I'd probably do that before a coil.

[burlmays9]

Start from the source of your problem and work your way back. Easiest way to diagnose something. It's quite hard (pretty much impossibe) to accurately diagnose electrical problems without a DMM so invest in one.

But since you've replaced what you have, I'd check out the condition of your cap and rotor like mentioned above.

[jlevie]

I doubt the problem is the coil, but check the connections. Coils seldom have intermittent failures. When they fail they completely fail.

Check the fusible line in the DME power lead. It could be corroded and browning out the DME.

[bmwguy325is]

Id check the wire thing out. A cap and rotor will generally cause poor running rather than no run at all.

[Wingnut]

Wow! such wonderful responses! Thank you all for your help!

Now for the update. I own two 325i's one is mine and one is my wife's. I swapped the coil to see if the problem would move. Interestingly, the problem completely disappeared in BOTH cars... I drove the car all day today with no problems at all. Must have been some oxidation in the coil ignition wire? high voltage is WEIRD!

-Wingnut

[Wingnut]

Most of the stuff I replaced was as old as the car... It was bound to fail some time. I also wanted a spare ECU. Made for a great way to justify to the wife since I was borrowing her car while mine was down. :)