Guys,

Need help and also an eye opener if your engine is lacking the fuel vapor pressure (purge) sensor like mine

The document : Overview of new features/modifications with introduction of new V-engine M276 with turbocharging ( SN00.00-P-0095A ) has the fuel vapor pressure (purge) sensor shown.


Mine is not USA version, hence I crossed out Code 494 USA




Also indicated in the working 101, as below :



Where is it by location ? Look for B4/4













Wiring schematic ...yep , B4/4 sensor exist





Amazing Mercedes !!!




Why was I going to this B4/4 sensor area ? Coz me fuel vapor purge valve is a bit louder than normal. It can almost compete with the injector at idle.
So while at it, I inspect all check valves on the fuel vapor hose assy.
I am sensitive to "new" noise.




I got another bad news for you guys M276 3.0TT owner.

Yep, MB seems to not sell the check-valve kit or the oil separator complete assy. This is all 100% plastic, so......... the two hose/pipe out of the oil separator will break for sure.

If the dual check valve kit failed, even either one failed, turbo boost will either go back/routed to the air filter or aftercooler or to oil separator assy


Thanks in advance for checking the pressure sensor B4/4 on your 3.0 TT.

 

This is the airflow direction and check-valves

Use ur imagination for leak/s scenario of the check valve/s

 

If I remember correctly someone with an CLS63 had a similar one that was blank and it failed. The replacement part was one that basically closed the loop. Let me see if I can find the video.

 

Thank you S.M ,

Tech note :
Without the B4/4 sensor, the ECM won't know if the fuel vapor purge valve Y58/1 stuck open mechanically.
Being a non USA model, my car does not come with the B4/3 fuel tank pressure sensor ( can read vacuum for sure ), which can double as back up vacuum negative pressure sensor.

I think I will exercise a test, to see if I can trigger : EVAP Related Codes P0411 P0440 P0442 P0446P0455, when and if I remove the Dummy sensor B4/4 ?
P0440 is an OBD-II generic code that the engine control module (ECM) has detected a leak in the fuel tank vapor system or a vapor pressure sensor has malfunctioned.


Something else is weird. The o-ring on the vent lines, its green color but the green is kinda a coating only, underneath it is black rubber ....WHAT ??? DUH !! Never seen such a thing.





This is a red o-ring. Seems like a BLANK B4/4 sensor too. A real sensor cant be that thin at the L bend. It has to be fat to house the pressure sensing module, just like a MAP sensor.

 

Tested 1 minute engine idling with the dummy sensor removed, engine sound like bloody vacuum cleaner....LOL.
The engine was fully warmed-up, it was after a 30 minutes run.
Did a short throttle blip to 4,000RPM too.

No engine check light triggered. Idling quality is decent because MAP sensor can accomodate the illegal extra air, unlike MAF sensor which if lots of fresh air by-passed it, poor idle will happen.

Hhmmm, this is no good. This means a missing safety parameter lost, due to the non existence pressure sensor

 

Good info here, sorry to bring up old thread. Just wanted to state that this is an issue with the pre-facelift 2018 C43 as well. I have been battling a high pressure purge line malfunction + small leak detected for a while now. Definitely have it narrowed down to either the check valves at the idle load line connecting to PCV vent, the check valve for high pressure purge line next to venturi nozzle, or possibly at this dummy sensor plug (I have a NA car, need to check to see if there is a sensor or not).

 

That is concerning, never heard of that issue on these cars before or maybe I am just not informed. Hopefully you get your car fixed soon.

 

Any follow up on this? I'm having an intermittent cold weather boost loss issue that sounds very similar to this and other S-Prihadi threads. Boost falls away around 2500rpm at mild acceleration and doesn't come back until a quick shutdown/restart of the car, and no codes are thrown.

EDIT: swapped in a new boost transducer tonight and back in business

 

I have a problem that is somewhere in these notes. Should I assume my check valve next to venturi is bad? I removed the unit, plugged the holes and blew through. The check valve is open left to right and closed right to left. Not completely closed though. A little bit of air gets through.