here's the story. there is obviously something going on with my "mix". when I bought the 1990 300E it did not pass inspection by .54 on the NOx reading, and the mechanic said to put some fuel injector cleaner into the gas and drive around then come back. Well I did that and now the NOx is fine but the CO went thru the roof!! 76.63!! what do I do. could it be the testers that are at the shop reading it wrong?? I doubt it ... but what are the options or steps that should be taken to fix the problem. does it have to do with fuel injection, the engine, of the exhaust? need help I only have until the end of the month before the inspection dates are expired.

i had the same problem with my 92 300ce. I had to replace my o2 sensor. Cost was about 300 total. I went and had it inspected immediatley and it passed with flying colors. Hope this helps.

If it is the oxygen sensor, then it might be worth looking at getting a universal one, and just splicing the plug of your original one on to it. The universal ones are about £35 here in the UK. I recently fitted one to a volvo and its perfect now, passed inspection no problem!

Ben

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Ben

'85 500 SEL
'85 928S2
'88 560 SEC
'90 750i

the car went into the shop today to have a five gas check on it??? supposedly to find out exactly why the cars emissions are off??? has any one heard of this? thanks for the feed back, it sounds as thought the response from the shop will be "replace your oxygen sensor" so I will keep you posted.

First, Don't use the after-market one size fits all O2 sensor. Second, Make sure the Cat is working. To test is simple, use a heat gun and make sure the outlet right after the Cat is hotter than the inlet, right before the cat. Third, have the shop make sure to test the O2, most sensors are not the problem, the shop just does not know how to test it. Fourth, the shop has to measure the current to the EHA and set the mixture control at the same time. Do that, and if everything is still not working right, drive it if you have not yet. FYI, the Cat will be ruined if it is running too lean, or too rich.
GVB

well ... finally got a call back from the shop and as it goes - I need to replace the oxygen sensors and it also had a cracked breather tube to the distributer cap? (I'm not sure on that one) in any case the techy assured me that the car is running fine and that it will pass inspection ...we will see

well ... don't know if the car will pass inspection, because now that the car came out of the shop it won't stay running!!! any suggestions now?

I respectfully disagree with your general statement "most sensors are not the problem." The older single wire O2 sensors become lethargic at approx 60k miles. The frequency of the O2 sensor signal begins to taper off at 60k, at 90k it simply needs to be replaced because the switching time is too great. Here is one very good reason to replace the O2 sensor every 60k on the older KE-Jetronic system-fuel is >$3.00 a gallon. The KE fuel injection system was not that efficient to begin with so a fresh O2 sensor that switches rapidly definately helps the wallet and the emmisions.

Most of the cars that I have been involved with that have had bad tailpipe emmisions here in Califonia had high NoX on their initial test. After installing new O2 sensor's and reseting the fuel mixture on the greater majority of those cars...they passed with flying colors. The O2 rule applies to either the KA-Jetronic system (Frequency valve) or the KE-Jetronic system (EHA on fuel distirbutor)

I agree with this. The O2 sensor and the feedback loop are a rare emission component whose operation helps mileage, performance, and emissions, unlike the crappy gas, low compression, retarded timing, EGR, and so on.

On the "Don't use non-original" sensor comment, unless there would be a problem with its physical inspection, I don't see why this would be a problem (don't know if they do this, the one I got for my car is also made by Bosch, looks just the same with a different connector, made for a Mustang. I know that people have used this part and passed emissions on my model car).

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86 560SL
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85 380SL
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Try adjusting the fuel mixture before you change the 02, thats if it scopes out somewhat ok.