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

[Sander11]

Hi!
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?

 

[bembo449]

cat convertor gone ?

 

[mattkh]

MIleage,,???

 

[Oldspanners]

If you've got oil in the after cat O2 sensor you'll never get the problem cleared and just fitting new sensors will allow the oil to destroy them. The oil wicking into the wiring harness is usually from the cam magnets which will probably need replacing and solid wire blockers will certainly need installed. You will also need to check the connector at the ECU at the side of the air filter for oil contamination.
I cleaned the connector at the lower O2 sensor with contact cleaner and compressed air many times over a period of weeks and did the same at the ECU carefully cleaning with cotton buds so as not to bend pins nor leave any cotton behind. Until you will have the harness free from oil you will never get correct readings to find any inherent faults.
If it's really bad then the harness is probably beyond saving.

 

[Sander11]

It has

MIleage,,???

It has got 160 000 km (100 000 miles)

 

[Sander11]

If you've got oil in the after cat O2 sensor you'll never get the problem cleared and just fitting new sensors will allow the oil to destroy them. The oil wicking into the wiring harness is usually from the cam magnets which will probably need replacing and solid wire blockers will certainly need installed. You will also need to check the connector at the ECU at the side of the air filter for oil contamination.
I cleaned the connector at the lower O2 sensor with contact cleaner and compressed air many times over a period of weeks and did the same at the ECU carefully cleaning with cotton buds so as not to bend pins nor leave any cotton behind. Until you will have the harness free from oil you will never get correct readings to find any inherent faults.
If it's really bad then the harness is probably beyond saving.

I checked the cam magnets and the electrical connections to them, they dont seem drenched in oil like the post cat o2 connector and I did not spot any new oil near the cam magnets or their wiring. I tried spraying down the connectors for both the o2 sensors today. The long circular connector for the post cat o2 was dripping oil when I took it apart. The pre cat o2 connector didnt seem nearly as bad tho. Do you know if the o2 sensors recover when their connectors have been cleaned or if they are just trash once oil has touched them? Also is there any way to tell if they are reading correctly?

 

[Oldspanners]

I checked the cam magnets and the electrical connections to them, they dont seem drenched in oil like the post cat o2 connector and I did not spot any new oil near the cam magnets or their wiring. I tried spraying down the connectors for both the o2 sensors today. The long circular connector for the post cat o2 was dripping oil when I took it apart. The pre cat o2 connector didnt seem nearly as bad tho. Do you know if the o2 sensors recover when their connectors have been cleaned or if they are just trash once oil has touched them? Also is there any way to tell if they are reading correctly?

The post cat sensor is the lowest point so that's naturally where the oil will collect. The oil wicks into the wiring through the copper wire strands and needs a blocker (solid copper) at the cam magnets to prevent this.
As for the sensors I would say that it depends how long the oil has been in the sensor but I didn't replace the after cat until I was sure it was completely dry and had problems with a near new NTK sensor and finally used a Bosch which I would recommend.
I would also inspect the connectors at the ECU as that will cause all sorts of problems.
Have a look at this superb video it will give you the info on sensors

Good luck.