Here we are again, dreaded smog time!

Today I smogged my '92 400E with 217,000 miles and it failed! What a pain in the ass! Now comes the fun of getting it to pass, and anyone who's had to deal with this knows just how great it can be.

I've searched past posts and have a fairly good idea of what the problem might be, but since there's some members of this forum who seem to be experts on this subject I thought why not see what you've got to say.

So a little info. about my car and the smog test results. As mentioned above, I have a 1992 400E with just over 217,000 miles, the car runs really well for it's age and mileage. Last smog test passed fairly well as I remember. The check engine light comes on occasionally, I believe the code it brings up refers to a communication issue between two of the computers, when I reset it usually stays off for about 2-4 months before coming back on. The cat. has that special smell only at certain times, like when going up hill under load and whatnot. Since I've owned the car I haven't done any work to any of the smog related parts. I think that the cat. is the culprit, but the O2 sensor might be to blame as well, it's only guess though.

Here are the test results:

15 MPH Test

RPM: 1350 - CO2: 14.1 - O2: 0.6
HC(PPM) MAX: 105 - GP: 280 - MEAS: 232
CO(%) MAX: 0.69 - GP: 2.19 - MEAS: 0.59
NO(PPM): MAX: 757 - GP: 1943 - MEAS: 2356

25 MPH Test

RPM: 1361 - CO2: 15.1 - O2: 0.2
HC(PPM) MAX: 80 - GP: 230 - MEAS: 102
CO(%) MAX: 0.56 - GP: 2.06 - MEAS: 0.15
NO(PPM) MAX: 696 - GP: 1743 - MEAS: 417

So, as you can see it passed some tests fine and others it just failed, and badly. If anyone as any input from these readings on what the problem might be I'm all ears. If it ends up that the whole system needs replacing I'll probably just end up buying another car, but I really don't want to do that since I love this car!

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500