new catback exhaust. CEL came on.
 

I had a custom catback exhaust built for my 99 986. Removed that HUGE exhaust and had a new free flowing catback system custom done. Sounds GREAT. But in less than 3 miles the CEL came on. never touched 02 censors. any ideas?

You have to tell us what the code is.

will not know till tomorrow. But the exhaust system is a complete muffler delete on 2 1/2" pipe. So basically no back pressure other than the CATS.

if you removed the cats completely, you might need mini cats for your down stream O2 sensors.

Something like these https://www.fvd.net/us-en/FVD111LAMSIM/oxygen-sensor-simulator-minicat-sold-individually.html

You don't have to get those exact ones, there are cheaper versions all over ebay and Summit Racing. I myself used the FVD because I ordered thier muffler as well at that time.