Has BMW AG developed correct test procedures? Has the N43/N53 series engines learned something?




Here is the test procedure for N54 engine. How to react, if there is a leaking injector.

Recommendations – circled with a red line.


And now imagine the typical situation.

There is a leaking injector in cylinder X. Because of this defect (the cause – injected increased fuel amount), Lambda is decreased in all bank (signal, which confirms, that the fuel mixture is very rich), MSD starts to rapidly decrease fuel supply for all bank.

As a result, the fuel mixture in damaged cylinder gets more correct, but in two other cylinders, Y and Z – the mixture becomes lean.

The rich mixture (within the limits of reasons) don’t initiate misfire, but lean – does. As a result – the error messages will be in cylinders Y and Z, not in damaged/guilty cylinder X.


According to the recommendation – the injectors of cylinders Y and Z have to be replaced, which also is often (unsuccessfully – without improvements) done…


This is a sample when the performance of manufacturer’s algorithm could be described with one word: FAIL.