CLK 200 Kompressor (M271 1.8L) Running rich and high CO emission

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New Member
Aug 24, 2023
Mercedes CLK 200 Kompressor (2003)
My car recently failed a emissions test because of too high CO. The car seems to be running rich too. I have not noticed the car running worse/rough or smell from exhaust but fuel consumption feels exsessive. The car is throwing the following DTC codes: P0170, P0137, P0172, P0138, P0136, P0141. The P0170 (Fuel Trim Bank 1) and P0172 (System Too Rich) seem to be the ones that return when cleared. It seems the bank 1 sensor 2 is just throwing codes at random and they dont immediatly return. I have changed both o2 sensors about a year ago along with the vacuum line under the air box. I checked the connection box on downstream o2 (sensor 2) and it was very oily. I checked the readings from both o2 sensors and they seemed responsive when applying throttle etc. The readings I got from o2 sensor 1 was about 1V at idle and peak at 3.157 when giving it some throttle. For sensor 2 I saw 0.35V ish at idle and peak at 1V with some throttle. I also checked the MAF which read 2.4g/s at idle and got up to 14.5 with some baby revs. I have spent some time looking for another vacuume leak but no luck. Also ordered spark plugs.
Anyone experienced the same thing or have tips or any idea what to do next?
Check the electrical connections to the cam magnets on the front of the engine for oil
The two round things on the top front
Hi! Thanks for the tip, I just checked and there did not seem to be any oil in there or comming from there.
That’s the extent of my experience I’m afraid buddy .
Good luck
If the spark plugs are due a change - that will likely help.
Can't figure out how you can see 3.157V from an O2 sensor. Usually they oscillate either side of 0.5V with zero Volts being extreme lean and 1.0V being the extremity of the rich measurement. The oscillation (AKA 'cross-counts) should be every few seconds. There are however O2 sensors that operate over a 5V range.
The cause of the richness - where I'd look first is dribbling or dirty injectors (assuming the O2 sensor data is as it should be). If you can get data on how long fuel pressure should take to decay when the engine is shut down, you may spot leaking/dribbling injectors if they are leaky. Not sure how to check for cleanliness and good spray pattern - probably need to have them checked professionally. When you change the plugs, they may offer up clues to specific cylinders being the cause (note which cylinders they are from if they are other than identically coloured (dark indicates rich)). Pressure regulators can play up but their effects are more dramatic. Nonetheless, check its hose that communicates with the inlet manifold for leaks or crimps.
I assume your emissions tester had the engine hot enough for the test and that the O2 sensors' heating circuits are operative. If not, it could be running open loop (default settings) though the O2 sensor feedback you are reading suggests otherwise.

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