aollaku

Hi folks,

I have a Mercedes Benz W221 S350 Bluetec 2013. For more than a month I`m experiencing an odd intermittent issue with the engine or maybe the transmission also. Is a bit difficult to explain my problem but I will try to describe it as best as I can. When I start the car in the morning everything runs well and no problem at all. After the engine reach 40C and above my problems appear. The car is shaking or jerking when I`m cruising at a constant speed (40 / 60 70 MPH). It feels like the car wants to change the gear and this symptom continue all the time with regular interval until the engine temp reaches 85C. After the engine reaches this temp, this symptom happens very rarer. I think is not a transmission issue because when I completely stop the car (on the semaphore for example) and leave the gearbox engaged on D the idle revs start to change (to goes up and down) until a point when the engine shutdown by itself. I need to start the engine and drive but the issue is the same until the engine reaches 85C. I`ve SDConnect (Xentry) scanning system and the only error I have is the NOX sensor which I`ve replaced twice with the original one from Mercedes Benz. Another thing to mention is that Bluetec is disabled or deactivated (deleted maybe) from the previous owner but never had problems before. My car has covered about 156000 miles. Please, folks can you help me to identify this problem? Please feel free to ask me any questions. I`ve tried to explain my problem as much as I can.

Best,
Andi

Arrie

Have you looked at the fuel pressure? It almost sounds like it is not burning fuel correctly before the engine heats up high enough, but this does not explain why it would run fine when it is cold from the start first, of course.

I do not know much about diesels other than they should run fine after they start and proper amount of fuel is injected in the engine with proper pressure thru injector to atomize the fuel for proper burning. Another issue pointing to the improper fuel burn is the NOX issue, which probably is not the sensor problem at all and you proved that already by replacing it twice.

Could it be that the car engine is programmed to act as it does if NOX levels are too high? This would explain why it works fine with cold engine as all the environmental engine controls are disabled until the engine reaches certain temperature, which could be that 40 degrees? After this point the controls start measuring things and finds NOX too high until the engine heats up to 85 and fuel starts burning better bringing NOX down and engine controls work better?

Have you looked at the engine temperature with your scanner or are you talking just about the one in the dash? It could be your electronic engine temperature signal is bad, which is not the same as what you see in the dash. I understand the dash gauge shows some sort of longer time "average" and is not the actual engine temperature.