re: "...Everytime I get my volvos inspected(every 2 years in NJ) I fail the NO test, change the CAT and WHA LA! I pass the test!..."

There's a guy on this forum who's a mechanic (I think Rule308) and who (he or whoever it really was) has stated many times, if you have to replace your catalytic converter for each inspection, you have what he calls a "Cat for a day" condition (or something like that). He's explained that this problem is typical of a poor air:fuel mixture that prematurely destroys your cat; and fixing this would let your cat last a long time, eliminating your need for this regular cat change.

I guess I've got a proper mixture -- I'm in New Jersey, too -- and my air:fuel mixture in my currently oldest 240, an '84 (non-turbo, automatic), seems not to hurt my cat and does well every inspection time. I haven't had to replace my cat in about 8 or ten years in that car! I also have two '93s, but they're recent acquisitions, so I can't claim them as an example of long-lasting cats, at least not yet. Besides these, the 240s I had before them were a '80 and an '83, but the inspection program didn't let me keep a paper copy of their scores (you undoubtedly remember the old days :-).

Here are my '84's results:

in July '04, with 193,289 miles:
NOx 33 (1227)
HC 27 (162)
CO 0.02 (0.91)
CO2 14.7 (no standard)

and in July '06 (just a few weeks ago) with 215,925 miles:
NOx 181 (1227)
HC 21 (162)
CO 0.12 (0.91)
CO2 15.0 (no standard)

I'd try to contact Rule308 (or whoever the guy was that I remember writing about this problem), and maybe you can get your car straightened out. Buying a new cat every two years is an expense you don't need, I'm sure -- and there is a solution to your problem somewhere.

I hope this helps.