I have looked over all the past posts on the board, and could not find the answer to my ? So here goes. I had the emissions tested today and failed again, same problem (oxides of nitrogen levels =NO). I just replaced the cat. It has about 10 miles on it. Completely stock rebuilt 79 350 with Q jet with all emissions stuff in place. My levels are __________ Reading _______Allowable HC-ppm _____ 11____________ 281 CO-% _____ 0.00____________2.26 NO-ppm ___3301 Fail_________1980 CO+CO2%__14.5_____________ 6.0 min. This is a load test at 25mph. After I replaced the cat. Everything went down except the NO level, which is what the cat is supposed to also reduce. It went up from 2474 from a pre cat test to 3301. Just about everything under the hood is new about 2000 miles. Am I correct in thinking by running it lean for the test it is upping the combustion temp, thus causing the high levels of NO. I've got a good idea on how to fix it, just would like other input, and what better place to find it than here? Right, It's great to be able to pick brains from a distance. This is a great resource guys. Thanks for any input.