M3 Check engine light finally cleared

In my previous post I thought the car was finally fixed—no more vacuum leaks and driving great. Turns out I was a bit too optimistic.

The next day that little bugger, the check engine light (CEL), came back on. Misfires, bad coils, O2 sensors gone awry. Car running like crap again. What to do?

I checked everything I could and couldn’t figure out where a possible vacuum leak was coming from. Sound tests and visual tests weren’t leading to anything; it was time to bite the bullet and bring the car into a shop.

Autoy & AutoWerke, an independent BMW, Audi, and VW shop in Rockville, MD came highly recommended to me so I brought my car over to the small shop.

An hour later Jon gave me a call and let me know they found a few things: the O2 sensors were backwards, an ignition coil was bad, and the ABS/ASC relay & sensor was bad. Not too bad overall.

Before I took my car to the shop, I thought the O2s might be backwards so I switched them myself but that didn’t help so I switched them back. Turns out I was missing one key piece to this: the adaption limits table in the computer. As you drive your car, it keeps track of various measurements (like how rich/lean it is running, O2 levels, etc…). Overtime this table is built up and the car works from there. When I switched the O2 sensors, it didn’t make a difference: the history of measurements said otherwise so the car went off of that. Turns out you need a special dealer computer tool to completely reset the adaption limits table, something I can’t do in my garage :-)

As for the ignition coil, that was a bummer, especially since I replaced those just about a year ago. Turns out BMW recalled the crappy Bremi coils on newer E46s and switched over to Bosch, but never bothered with the E36s. So basically those things are going to crap out and nothing to do about it, doh!

With the O2s correctly connected now, the adaption limits reset in the computer, a new ignition coil, and new ABS/ASC relays and sensor, the car was running fantastic!!!

The M50 manifold gave the car a very nice rumble, especially at WOT, and I could really feel it start pulling right around 3500rpm.

My car is finally a joy to drive around! Not only that, but I passed inspection and can now legally drive it again, grin

Next up: rebuilding the suspension, spring 2008 :-)