Hello everyone i have been getting a check engine light at random times. i have an 05 s2k with 58k on it. i do have a 70mm testpipe (no cat)with the defouler trick so the CEL wouldnt come on and 3inch catback system. I scanned my car and 1 code popped up showing misfire on cylinder 3,so i changed all spark plugs and cylinder 3 coilpack then 1hr later scanned again and 3 codes popped up showing random misfire, misfire cylinder 1&3. all codes erased by it self without me clearing it and a couple days later the codes came back. Can someone please help. Its driving me crazy. Could the ecu be screwing with me because of no cat. It does idle funny but i thought because of the exhaust. Thank you everyone for your help.

 

What spark plugs did you get? OEM? check your spark plug gap for 1 and 3.

Or put back the old spark plugs from the cylinder where they came from and leave in the new cyl 3 coil. Reset your cel and see if it comes up again. If misfire cylinder 3 again, then put in the new spark plugs but check the gaps.