Posted by John in Simi Valley on July 06, 2008 at 20:00:18 from 75.33.103.6
In Reply to: OT - No spark on e28 535i posted by Nate in Pitt, from SLC on July 06, 2008 at 15:49:47:
Nate,
These intermittent electrical problems are the worst. You can troubleshoot all you want, but untill the failure mode shows itself again, you're just guessing.
As Techboy says, it could be a sensor. (Jiggle the wires while it's idling). As you mention, it could be the ECU. I doubt it's the coil - they rarely go bad unless you see damage or corrosion.
Which brings me to my reply -- CLEAN ALL YOUR CONTACTS. In the comupter age, a ton of problems can be traced to poor contacts. Start with the simple things first. Go to radio Shack, get some good spray-on contact cleaner. May want to start with brake cleaning fluid first - it's cheap and easy.
If you need a replacement '059 ECU, Matt has some, very reasonably priced. Matt is at jspec20@hotmail.com
First contact is your GROUND terminals - unbolt, wire brush, spray with cleaner, grease with electrical preservative grease. Wurth sells some stuff in a toothpaste tube ($30-bucks?) but one tube lasts many years. Synthetic grease is okay too. Hit the sensor contacts, AFM, ECU, disconnect the coil wires one terminal at a time.
Strongly consider replacing ALL the fuses in the fuse box - whether they look good or not. If nothing else, at least you'll know what's not the problem.
Good Luck