WTF? check engine light and drink gas

[Tree]

so the other day, i swapped out my header, and i had to run a damn open header, so after driving like 5 miles my check engine light came on, but i did not worry about it because i was running the open header, so the next day i got my hi-flow cat on and my skunk 2 cat-back on, and i was driving down the road and it came back on..... and i don't know why, then today i was looking at how much gas my car was sucking up. what the hell can it be?? can me 02 be going bad? i really need the help... if you can help i will give reps.

[Humphrizzle]

clean the O2 sensor.. reset ECU to make up for more exhaust emmissions going through the sensor..

[mitch lab]

jump the ecu for codes.

[Formally...]

^ like he said you need to jump the ecu and find out what the codes are. That will tell you where to start.

[bowdown201]

mine chuged gas for a few days and ran kinda weird but turned out to be a map sensor

[Tree]

i found out its the 02 was not hooked up.. opps. but thanks to tom he helped me. thanks for the help