Car only backfires when accelerating at any rpm

Waterchicken said:

Just installed Megan racing headers on my tc1, first couple of days were fine and out of nowhere check engine light starts flashing and car was only backfiring when getting on the gas. I have an 02 sensor "bypass" but idk if it's faulty. NEED HELP ASAP

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OK, I'm old school, and I don't follow all the new stuff, but that back fire is increase fuel of unburn gas. Your stock head may have a fuel trim sensor (usually four wires) that works in conjunction with your O2 sensor (two wires). If your new heads don't allow the fuel sensor, and there is no mod for the car cpu, then I fail to see how the car knows the proper fuel/air ratio. When you first ran the car the cpu stayed at the right ratio, but when it lack the input from the fuel trim it LEARNED a different ratio, hence the back fire. Not only will end up ruin valves but WILL destroy your cat converter if you continue to run the engine..

Waterchicken said:

thank you for the knowledge, would you suggest I mess with the wiring on the o2 sensor or put on a stock header? Or something else? Again thank you

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Your car cpu looks for the imputs to give the proper fuel mixture. I do believe the one in front of the cat converter is the fuel trim sensor (can't just leave it off) as opposed to the O2 sensor. Again not knowing the exhaust heads, does it have a threaded port for the fuel trim? If yes, put it back on and the cpu will correct itself BUT don't high rev it. If not, then check Megan if they make heads with it. Otherwise, you need further modification, most likely a different racing cpu that will not use the fuel trim sensor as a way for controlling the fuel/air mixture.