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Hi. I recently replaced my ECU (it seems to have fixed the issues I was having - gas/temp gauge, key stuck in ignition, TC & Security light on) and now that I have the new one in, my car is running super rough. The diagnostics are showing a misfire at cylinder #5. I replaced the coil but it did nothing. It was recommended that I try replacing the spark plug, which I will do tomorrow. So my question is why would my car be running fine with the bad ECU and now that I have the new one I have a misfire? I even put the old one back on and the car runs fine. I'm hoping someone can help me make some sense of this. Thanks in advance.
 

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2010 Black CTS 3.6L RWD , 2010 Silver CTS 3.6L RWD
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If you put the old one on a it runs fine then it sure sounds like an ECU prob. It may have fixed your initial problems but created new ones.
 

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Thank you. The more I think about it the more that's what my husband and myself are thinking. I'm going to call the company I got the ECU from and ask for a replacement. I'm thinking they coded it incorrectly and there really isn't a misfire. Just think it's coded wrong which is making the car run the way it is. Do you know if it can be re-flashed at my dealer even if it has already been? Thanks again.
 
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