the dreaded check engine light :[
 

I just got my X pipe and catback exaust put on yesterday, (both are SLP) and this morning on the way to church, my check engine light came on.... any ideas. like a sensor or something??

get some Mil eliminators

Is it a catted or offroad X pipe? If its an offroad x pipe then do what Stan said. These have to go inline with back O2 senors. They tell the ECM that all is lovely.

In his sig it says catted x pipe. The cel could still trip even with the catted x pipe. I'd say get a handheld programmer especially if you plan on modding your car more.

I'm gonna have the shop double check the sensors and such, but the programmer probobly wouldn't hurt... I need paychecks =[ lol

what would the chip / tuner change to fix the problem, cause the motor is also running really rich...

With the tuner you could turn off the rear o2 sensors which come on usually after installing an o/r mid pipe...but an aftermarket catted midpipe can trip the cel. The mil eliminators would do the same thing the tuner would but that's it. With the tuner you get a performance tune right out of the box and the opportunity to get a custom tune at a local shop. Not to mention you can read cel codes and fix speedo changes if you add gears etc.

Get the tuner and a custom tune at a local shop. That way you can have piece of mind and better performance all in one.

disable rear sensors in the tune and the problem usually goes away.

well this was easy... I just disconnected the Negative battery terminal for 30 minutes, and reconnected it, then let the car idle for about 15... it idled really really wierd for about 5 minutes then the computer reset and it not only idles like it should, it's running better than I could have ever amigined. and to top it all off... the light is gone!!!! =] =] =]

The light may still come back...

In the 99-04 mustangs when you disconect the battery it does clear the CEL but it takes your computer like something crazy around 30 starts or something close to read your car and if it is a problem it will come back on, plus with a different midpipe it may be running to rich/lean on the left or right bank and thats as simple as adjusting it with a tuner.