emissions problem

[03 COBRA SB]

Needed to have a emissions test for the first time(after 5 years). I failed the NOx emission. Has anyone else had any problems with this?. Are the after market high flow cat's causing this? Can the K & N intake be the problem. I have a custom tune that sanbandit did a couple years ago with the predator. Anybody have any idea's.
Chris

 

[PhillyCobra]

NOx can be high from EGR problem. It goes up with high combustion temps, and EGR cools combustion. Is your EGR hooked up and working properly?

I guess it could also be a cat problem, as modern cats both clean out HC and CO (oxidation) and NO (reduction).