2001 Z3 2.5l Misfire

[rnettleship]

I'm new to the forum and could not find threads searching on "misfire"....

I have 45k miles on the car and last year I noticed a misfire under a specific scenario which I cannot always repeat but it is consistent. As far as I can tell the engine runs fine at cruinsing speeds and the problem never happens in a gear higher than 2nd.

The misfire happens at low speed, ususally when making a turn and down shifting into 2nd gear or slowing for a traffic light that changes to green before I stop. Under acceleration with RPM between 1k and 2k the engine can have a minor or extreme misfire condition. (Not backfre). As soon as the RPM's get over 2k it clears up and runs great. I never sense the misfire when accelerating from a complete stop in 1st gear but when shifting to 2nd it would be rare for the RPM to be under 2k anyway. I do not usually get any codes from the ECU. I took it to a dealer who told me they would change the ECU and wireing harness for $2k which is not an option. They also said they did not believe it was a coil pack as they swapped a few they had and the problem did not go away.

An interesting point is I tried replacing the plugs with non-standard ones that required a gap adjustment and the car was almost undriveable. It seemed like all cylinders were misfiring. Put the old plugs back and it ran fine but with the original problem. Given the scenario that brings out the problem I am wondering if it could be related to fuel delivery instead of spark. Could I have a fuel injector that is dumping too much fuel at low rpm?

[98Z]

Though your prob could have multiple explanations, it sounds like it is in the fuel management system. Highly doubt ECU unless it is a common concern for your vehicle. I own a 1.9 Z3 and it would abruptly stall in mid stream (usually during acceleration in 2nd or 3rd. I went to Auto zone for free plug in diagnostics. It was a camshaft position sensor. I picked up BMW part, replaced it, and it runs great again. OBD (on board diagnostics) check will shorten your research tremendously. Use a parts store for diag.