Originally Posted by sambonator
...Maybe BMW came up with a new ECU program that trigger issues when piggybacks are detected. This began to occur after he got the car back from service, so a new ECU program may have been loaded.
...Perhaps this is the 1st sign of issues with the N54 engine and increased boost mods. Dinan (and others) have said in the past that cylinders 5 and 6 lack adequate cooling capacity for big power performance mods...
On the first thought, I would not believe to be the case. It is my understanding that misfire detection is done by monitoring the frequency of the CPK signal (crank position sensor) and possibly the cams position sensors. If a misfire occurs the acceleration of the engine briefly slows and then speeds up again. The DME will pick up this momentary lag and know which cylinder fired. It normally does not do set a code on a single misfire detection but after several (perhaps fifteen or so) a code would be triggered.
Playing devil's advocate for a moment though, since the PROcede does have the ability to retard timing some, I could see a single or a few detections might be triggered since there would be an immediate pull back in the phase. This could be construed as a misfire. However, I highly doubt that this would only be seen on a single cylinder. If an update to the DME could try and detect a piggyback system this way, I would highly suspect that P0306 would not be the singular code but rather P0300 would be thrown. P0300 is a random misfire code.
On the second matter, if it were a general weakness I would suspect that we would see this with more vehicles at this time. While limp mode has occurred with others, it has not been due to a misfire detection on a single cylinder for the vast majority. And of that majority, most were boost target not being reached codes or octane issues.
This issue intrigues me as it is not all surprising. Why I say that is due to experience in seeing unique issues with certain cars occur across all makes and models when modified. There will always be a few cars which have inherent issues (may not be the case here, just commenting) that only appear when the load is increased. Often times these issues do show up in stock form at some point though. Heck, (although unlikely) could a cam have been installed and be off by one tooth or jumped (very highly unlikely) at some point. In the end, this is the issue with modifications; some will never have problems, while others will be plagued.