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Hey all, it's been awhile since I've been on here. Well I'm having some serious vapor lock of the brain, as bill Fulton would say.
I've got this 2007 Mercedes benz c230 with the v6 272 engine in it. C/S CEL on, generic bid codes p0172 p0175 both banks lean.
Stft 5% ltft .9% MAF at idle is reading 4.7 g/s at WOT calculated load goes to 99%. Freeze frame caught fault at idle fuel trims should very close to 0.
Now I run fault with Mercedes SDS and find rich at idle left and right banks fault codes. Now here is where my mind is locked up. If you have every used the SDS any fault you have it will suggest tests and checks for the fault. It was telling me to check maf, lambda sensors air leaks in exhaust and fuel injectors. Now this car runs fine. My lambda sensors read .980 as low as .880 which I think a lean exhaust. As soon as create a vacuum leak lambda sensors rise above 1.0. If you enter fault code in identification it tells you that it can be caused by MAF, or air box not seated fully on the MAF, leak in intak manfold or fuel pressure. This has completely thrown me off from all that I've learned of fuel trim. Why would it set a rich fault but show me lean trims. Yes okay to much air in exhaust so injector pulse is commanded on longer. Any help would be appreciated it seems to me that MB fuel trims are backwards
Hello Eurotech as I recall p0172 and p0175 are rich? The maf is common for causing this and is where I would start looking. All these tests must be done with engine fully warmed up at idle check maf and fuel trims and o2 sensors and again at a wide open throttle test drive.also check fuel pressure to make sure it's not to high. There are no misfired correct?
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