what will fail emmisions on my 02 GT regardless of were im at much appreciated. Thanks.

 

a check engine light will fail emissions. On 96+ vehicles all they do is plug it in. I just passed emissions with a o/r h pipe. All you need is a handheld tuner to turn off the rear o2 sensors or a set of mils.

 

There are a variety of things that can effect the emissions quality of your mustang. Exhaust (long tubes, o/r pipe w/o MIL eliminators or tuner), harsh cams, EGR sensor that is effed up, etc. If the parts are marked 50 state legal they should be okay (designed for maximum performance output while staying emissions legal).