I would take a look at the cylinder-selective injector adaptation readings in INPA...MSD80 -> F5 -> Shift-F6 -> F1
Per the engine management training module (page 36):
http://www.e90post.com/forums/attach...8&d=1165592709
Adaptation of the injector opening signal is based on smooth running monitoring of the engine. My guess is that the injection time (einspritzzeit) for cylinder 4 will be skewed when compared to the rest.