Heya, having a bit of trouble troubleshooting something and would appreciate any thoughts
My 02 SLK keeps spitting up an engine light and codes for the fuel mix at idle being too lean, and this matches how it runs at idle in terms of revs. It's potentially moaning about something in cylinder 4 and something seems seriously off with at least 1 lambda sensor, the upstream one's voltage is all over the place between 60-800mV odd, and it's in red text. I don't have much skill with electronics but that doesn't look good.
By contrast the downstream sensor voltage is stable, but it's warning me in red text that heating capacity is reduced...I'm bit vague on this, but the Lambda sensor is the same as the O2 sensor? it's measuring the fuel:air ratio so a likely culprit?
A bit of back story on what i've done so far to the
chatroulette engine, i'll try and be brief..
It had an EML on when i got it, and was assured it was was a sensor (lying £%^$!
) I got a scanner and got motor errors for hot film warning on the Mass Air Sensor
cyberghost and something indicating a misaligned/broken rod in my intake manifold (NOT the code i'm having now) . cleaning the MAS didn't help much, and it also looked suspiciously new as if someone had already been trying this...
Did a fair bit of youtube research and determined a likely culprit was a clogged Positive Crankcase Ventilation system spitting waste oil back into the intake, so it would follow that the MAS keeps getting new faults...this meant taking most of the intake/throttle system and the intake manifold out, along with a variety of for want of a better word, car guts. Cleaned everything out and replaced the whole PCV with OEM parts along with a few other gaskets and vacuum pipes...
Doing this has deffo solved the my two initial codes for the MAS and the Intake Manifold, but it's only THEN this 'running too lean at idle' has cropped up :/
I can't find it atm, but a random forum post tipped me off to an issue with this engine where waste oil gets into the socket of a wiring loom at the front of the crankcase and basically wicks it's way up the wiring towards the ECU, not sure offhand but i think this loom is the one a lot of the sensors run off. I checked that socket and yep, it was soaked, def to the point i'd expect it be causing an issue. Apparently there's enough metal particles to mess up voltage but again, not really my field, could that be throwing my lambda sensor off?
It was a few weeks ago i did this and cleaned it out, I've checked the socket twice since and it's been wet (but less so) both times...I don't believe NEW oil is getting in that quick (I degreased the crankcase to keep an eye out for fresh leaks), so does this mean it's kind of 'draining' it back out the wiring loom? *looks hopeful*
A few articles are tipping me off that the idle fault could be down to the PCV being incorrectly hooked up, but i'm 100% it's right, it wasn't complicated to replace. The fuel pressure or injectors could also be a culprit...and i had those out for cleaning when i did the other stuff...possible that could tally with the fault readings from cylinder 4?
Cheers if you read this far, just curious if anything occurs to anyone