Failed emissions AGAIN! (new #'s)
 

There were a couple of threads on this subject recently, although I don't think either one actually went to a conclusion unfortunately. Anyway, it sounds like an O2 sensor. There are threads telling how to test that.
Mike

Which car is this on, the 300E? If so, how old is the O2 sensor?

This is on the C280. The car was recently purchased so I don't know how old the 02 sensor is.

I'm going to run some tests (pull codes, etc.), change plugs and oil and see what I can turn up.

I don't understand though why HC's would jump so high when reducing NOx.

Thanks for the replies. :D

If it is the O2 sensor, it should store a fault code. That car has 2 O2 sensors. What did you do to reduce the NOx, replace the cat?

Typicly what causes high NOx readings...which on a Gas engine is a lean misture indication. and therefor high combustion temps.....fattening up the mixture to reduce that will rais the HC's .......also a bad cat will give horrible HC's.


How many miles are on the engine? I would run a can of BG products BG44K......thats the best injector and combustion chamber cleaner I have personally used.

Perplexing. Repairing a clogged EGR tube should not upset the mixture and cause a rich condition, which is indicated by the numbers. Regardless of EGR, the lamda system should maintain a stoiciometric mixture, and your HC and CO emissions should not have changed signficantly.

As stated, check codes and O2 sensor function. Did something inadvertantly get disconnected or reconnected incorrectly while you were working on the EGR tube?

Duke

A bad O2 sensor will not necessarily cause fault codes. It can be "sluggish" but still read "OK" by the computer. That was the situation with my 86 Toyota. Not sure if that holds true for Mercedes but it could. As I have said before my Toyota's system is L-Jetronic based, so is a Bosch based system.

MP

There is something wrong with this picture. I have been doing smogs for 20 years so i have some clue on cars. Anyway the nox repair went very well. Looks like you did the correct repair the first time. You would be supprised how often people fix every thing but the right thing. :eek:
So you had great co the first time and now car is not in fuel control. should have about .15 co give or take a little.
So first check to make sure no wires were left off during the repair, most likley cause.Also check for air leak after the m.a.f sensor. :dead:
Co can go nuts like this if coolant temp sensor is disconnect or out of range. Shold throw a code if its that bad.
Second your intake air temp sensor,is it disconnnected? If its on , if its hooked up move to the 02 sensor. Hooked up? Maybe its drifting or out of range. Some times no codes and most likely cause of co problem.
One more important item i almost forgot, you moved the wire harness around alot during the repair,this could make all those sensors act up. Double check to see if the wires are not falling apart, this should be the first thing done.
fixing nox is no reason for co to go crazy.
Good luck
Rich :D