2005Diesel said:
Depends on your state, some care, some don't. Unfortunately mine does, I'm in NC.
its not really left to the "state" to decide, its a federal law and some
more densely populated areas must preform more strict testing (sniff
test w/ tail pipe probes or dynos)
the fact of the matter is that a cat can not work w/out O2 sensors
installed at least PRE cat...and todays gasoline based cats work better
because of pre & POST O2 sensors.
w/out O2 sensors you can not monitor the mixture or how well (if at
all) a cat is working.
the cats on diesel trucks are little more than SOOT traps (diesels dont
polute hydrocarbons like gasoline engines anyway)...most states are not
"used" to seeing cats on diesel trucks (or cars)...
simply put they dont even know to look for 'em much less what
years they were installed and NOT installed on (ford in particular
has installed cats on diesels off and on for years)
very very FEW areas have emmissions testing for diesels (az has some).
i live in the 4th largest metro area in the USA & all they do is check
the lights, horn & brakes (brakes are a seat of the pants drive/hit
the brake pedal test...it too is a joke)...no one has ever considered
looking under my truck.
i dont knwo if nc has diesel emmissions (yet)...but if its a visual
inspection and they are looking under your truck....try another
shop/tech (or use the mbrp test pipe...it bolts in and out to
the factory plumbing)