As time goes on, I have seen more and more BMW petrol engines (especially N43/N53 series), many diagnostics have been performed. It is getting harder to surprise me. But – this time, the user of the car with the N53 series engine did it.

The car owner approached me, claiming that the NOXEM has been installed; all service procedures were performed correctly (registration of new catalytic converter and re-adaptation of the engine), but the engine does not run in. Stratified charge mode, but in Homogeneouys lean!

He sent me the screenshot as a confirmation:

True, the engine stubbornly works in Homogeneous lean mode! What could be the reason? Reduced performance of the NOx catalytic converter won’t be the one to blame – it could be a problem if an OEM NOx sensor would be installed. Short-term problems with CO catalytic converters? Also, no – then the engine is supposed to switch to Homogeneous mode, warm up the catalytic converters; after time, it would restore the Stratified charge. The only one reason, which stays – misfires! Yes, misfires can cause such problems. 

The car owner informed me that recently new NGK spark plugs and Bosch ignition coils were installed. Defective? I doubt!

I asked you to send me the data of the fuel mixture in injectors. Everything is correct! So, the leaking of the injectors, bad atomization are not to blame. Does really any of the injectors have an incorrect beam, which is too close (drowns it) or too far (the fuel mixture in the place of spark too lean) to the spark plug?

Next step – checking the misfire counters in OBD Mode 6. Here are the data:

If the first bank’s situation is quite suspicious (0/6; 0/6; 0/10), then in the second bank, it is tragical (0/3; 16/105; 15/129)!

What is happening? I imagined the diagnose of the standard service: injectors! They have to be replaced! Estimate: 2000 EUR! But I don’t believe in such inexplicable injector damages.

Together with misfire counters, the car owner sent me also the video of the cold start. Here is the screenshot:

What looks quite funny? The mechanical efficiency of all cylinders is increased! How is that possible? DME has gone crazy? Incorrect software?

Do you see the marked learnbit? It is white – uncolored! What is that for a learnbit? It is the learnbit of the flywheel sensor and the tooth ring adaptations.

What does this learnbit, why is it necessary? 

To ensure the engine’s maxed even performance, DME measures each cylinder’s parameters (its injector) and compensates even the slightest difference from ideal. To perform this task, the crankshaft sensor has to give accurate data regarding the engine’s performance. Only an accurate sensor can give accurate data. For the sensor to perform accurately, there are adaptations intended for it (and the toothed wheel, which it is reading). So – at first, the sensor itself is calibrated; next – the toothwheel, only after the DME can measure and adjust the cylinders’ performance. How are these adaptations (of the crankshaft sensor and toothed wheel) performed? It is described in the blog – everyone can find this procedure. 

Note. If the car is equipped with an automatic gearbox, in theory: after some time, DME may adapt the flywheel sensor without performing a specific service procedure. But even in such a case, the injector adaptations will be performed incorrectly; the engine will vibrate, there will be misfires, complaints regarding the engine’s uneven performance, etc. If the car is equipped with a manual gearbox: everything depends on the habits of the car user and the driving profile. But, even often braking with the engine (driving in Overrun mode) there is a small possibility that the car owner will succeed in creating correct (and quick/directly after deleting old ones) adaptations of the flywheel sensor. And again – all previously mentioned problems guaranteed!

Obviously, the owner of the car hasn’t followed the procedure of the engine re-adaptation!

In this case, DME reads incorrect information from an unadapted flywheel. Accordingly, it corrects each cylinder’s performance in a completely incorrect way; as a result, misfires appear (due to incorrect fuel mixture). The engine can not be used normally – it vibrates, shivers. Besides, the vibration can be felt even when/if Rough run data indicate all cylinders’ identical performance!

Sentence of this entry: if your diagnostics specials claims following:

“it is not necessary to perform the re-adaptation of the engine after engine repair works”;

“I will delete adaptations – DME will do everything by itself; you just have to drive”;

“The engine adaptations actually are not important”, etc. – keep away from such “diagnostics specialists”! 

P.S. of course, depending on the situation: the engine can also have other problems, for example – leaking injectors, etc. If correct adaptations of the flywheel are not created, you can not trust anything – not the measurements of mechanical efficiency of cylinders, not injection adaptations, nor misfire data!