BMW E90 N54 injector leak and cold start shaking
E90 N54 shakes on a cold start and gives misfire codes, what causes it?
A common cause is a leaking injector. The injector leaves extra petrol on top of the spark plug, and ignition fails during the cold start enrichment phase. The plug is wet and smells of petrol.
How is a leaking injector diagnosed on an N54?
A wet spark plug and injector tip point to a leak. The injector can be swapped to another cylinder: if the misfire moves with it, the fault is in the injector. In the log, look at the air-fuel ratio and the fuel trim values.
Do all N54 injectors need replacing when one leaks?
It depends on the injector version. Versions 11 and newer are calibrated differently from version 10 and older, and they must not be mixed in the same cylinder bank. With the newer ones it is enough to replace the faulty ones; with older ones the whole bank is replaced. BMW recommends replacing all of them. A new injector is coded to the car.
Is there a service campaign for N54 injector leaks?
The injector campaign has been open for a long time and it is free. You can ask the BMW dealer whether it has been done on the car; if the car has been serviced at a BMW dealer, the campaign has probably already been done.