Our '96 v-8 t-bird failed an emission test today. The HC was 53ppm,two and three years ago it was only 24 and 10ppm.The NO was 9ppm three years ago,two years ago it was 186ppm.Today,the NO was 244ppm (max is 409).We did have to gut one pre-cat due to it self destructing when a broken vacuum line caused several cylinders to lean misfire,which led to raw fuel igniting in the cats (and doing a meltdown).The vacuum line may have been an increasing hidden leak for several years before the big breakaway.Today's failed test seems not related to a gutted cat because cats are supposed to control NO more than anything else,right?The car currently has MSD ign wires,new plugs,clean air filter,new fuel filter,Dynomax dual exhaust,no vacuum leaks,and all original maf and oxy sensors. Fuel mileage around town is poor,averaging 13 to 14,but freeway mileage goes up to about 23mpg. I am thinking (guessing) that if the oxy sensors are "slow" maybe that degrades city mileage,wastes fuel and raises HC levels.What do you guys think? Also,would cleaning the maf have an emissions advantage?The car starts easily,has pretty good power,does not show a check eng light,and has no stored codes.I would like fix the problem and pass with a large margin.I've got four weeks until current registration expires.Every good tip would be very appreciated!