Sometimes I feel that I have mentioned all possible engine problems in my blog. But the experience shows that the mistakes are repeated again and again. That’s why I continue to write about the experience of others, so you don’t have to test it by yourself.
Today’s customer: the owner of the vehicle with the N53 series engine. Sometimes a permanent vibration of the engine can be felt at idle. The error messages indicated a reduced Lambda value in Overrun mode, reported by the NOx sensor. The error message is sporadic, obviously, really – some of the injectors are leaking in closed condition.
Initial live data and the injector adaptation data did not indicate the problem – at the moment when the test was performed; the car was working correctly. I instructed the customer to take screenshots of the exact menu at the moment when he will feel the vibration.
The customer decided that he would act differently. He gave the injectors for testing (I was not informed about that) and, if necessary, also for cleaning. This time all was limited only to testing because tests have confirmed that all injectors are working correctly. Well, I have to add that the tests, according to the owner of the car, were performed in 5 bar pressure. And – at the room temperature. The Rail pressure of these engines is 200 bar – 40 (!) times higher than the test pressure. It is only logical that these “tests” will not indicate any leakages.
After installing the tested injectors back, the next cold start started with a significant permanent vibration (significantly stronger than previously). This time the owner of the car performed the data recording. I will insert two screenshots from the video that clearly indicate the situation:

Here, the initial fuel mixture of both banks has been rich. For the first bank, it was enough with a condition of -28% to reach the Stoichiometric fuel mixture. In the second bank, even with a correction of -30%, the fuel mixture is still rich.

Here, the data on the mechanical efficiency of cylinders confirm that the injectors of cylinders No.1, 3, 4, and 6. In addition, this leaking is not catastrophic (all cylinders continue to work – group misfires haven’t started), but exactly such – limited (but strongly over allowed norm) leakage is typical for the injector “cleaning” procedure and/or use of fuel additives. That was the reason for my first question – were the injectors cleaned? No, they were only tested – the owner of the car honestly answered.
Why does it happen like that? The liquid which is washed through injectors during testing is the same liquid used during the cleaning of the injectors! This liquid is full of microparticles from previous cleanings! These microparticles are the ones that get stuck in the nozzle of the injectors and cause leaking. In addition, it is not possible to get these microparticles out of the nozzle anymore, for example, by dissolving them because this liquid does not dissolve these microparticles! Because, if they dissolved, they would do that a long time ago! So, the injectors are damaged and should be replaced. One wrong decision, and losses of around EUR 2000.