I have a 2004 MCS with 105 kmi, 15% pulley, alta CAI, unichip, and recently installed an alta cat-back. With-in 2 cold starts of installing the exhaust i got a check engine light. Every 3rd start (the reset # of cycles to clear a code) the code goes away for about 5 or 6 cold starts before returning. The CEL only comes back after a cold start.

I have not yet had the code scanned, but since it only occurs during cold start-up, and it has only become an issue since installing the exhaust along with the high mileage of my car, i think it may be related to the decreased efficiency of the cat at lower than operating temperatures. Coupled with the higher flow rate exhaust which decreases the residence time for the ox/redox reactions to occur which results in a cat product gas being at below threshold efficiency which results in the CEL

Are there any other ideas as to what may be the cause, i will get the code scanned later today or tomorrow. Also the CEL doesn't bother me too much, but are there any simple ways to eliminate the light other than a 2nd o2 sensor cheater?

-Michael

 

Getting the code will point you in the general direction of the problem and help eliminate all of the "what if's" and prevent possibly exploring the multitude of ways to fix an exhaust related CEL.