mach 1 low miles

I bought a 2003 Mach 1 with 13k mikes on it. It had a supercharger put on it by previous owner who worked for Ford. I had it emissions tested yesterday, and it failed due to high nox. I’m wondering what the possibilities for cause could be. I don’t pretend to know anything about engines. My...

I am listing a 2004 Mustang Mach 1. The car has 31,317 miles on it and has always been stored in a garage. It has never seen snow and only seen rain when caught out in a storm. Only mods are a Borla catback exhaust and K&N drop in filter. Located in Cincinnati, OH asking $18,000 OBO.