what causes high nox?

 

high compression

 

temp of the head to high

 

lean mixture, bad o2 sensors, timing off, bad cats, clogged or nonfunctional egr valves, among other things

 

get a cheap 50 cat from a muffler shop right before you get it tested, it will pass, thats what i did cuz i had high nox. after about a week or so the cat stops working, thats what u get for 50 bucks i guess.

 

high nox is caused by modified camshafts and high temp in the chambers, probably from a lean mixture. You could richen your mixture to lower nox but that can bump up hydrocarbons so you'll need a working cat to counterbalance that. Also make sure you have your O2 sensors working properly because they can cause lean fuel sometimes.