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-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi

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

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

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

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

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.

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-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi

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?

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

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.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

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

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

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.
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.
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

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88 300E White, sold 9-04
88 190E Black 2.3 sold
90 300CE White, Grey sold 12-24-04
92 400E White,Grey Sold 5-06
90 300CE 91K Signal Red,Black Sold 2007
1989 300CE Smoke silver,Tan Sold 1-08
1993 300E 3.2 M104 motor
1991 300CE White,Grey
1994 E420 beautiful car,gone to new home
1994 E320 Smoke an Parchment.Beautiful car