I know that too much voltage can cause damage to the electrical system but what type of damage can it cause. Before I changed alternators mine peaked at 18+ volts and I have no idea how long it was bad. Could this high voltage damage a battery or cause ecu problems that wouldn't through a code. My old engine was running flawless then it went dead barely running. I put in a 66000 mile replacement a6 from a wrecked si and it was flawless but now at idle its going poop poop poop out the exhaust pipe. I have no hesitation and during deceleration in 3rd gear it causes more popping noises. I guess I'm just wondering what things I need to recheck to make sure this winter will go good. I had been using a ecu from a 88 si and after I changed back to mine it seemed to get better but I don't know these problems are all intermittent here now but gone at lunch time.