used ecu ,car wont start?
 

have 2000 galant 4 cylinder. whenever i drive it with the ac on it starts to hesitate and putter and when the ac is off it rides fine. the other day i tried to turn on the ac and cylinder 2 coil started to smoke whenever i took it to get ses light checked it read random multiple misfires so i took it to a mechanic and he thinks the ac wires sorted the ecu and the coils. i changed the coil and the car runs fine expect when the ac is on . we removed the ecu and noticed one of the chips were burnt and so we tried replacing ith with another used and it didnt crank up just turns over so we got another used one with the same serial numbers and it still wont crank up but my old ecu lets it start up fine. Dealer says it may have to be reprogramed and to bring it in but im afraid there going to try and somethings going to happen again and there not going to be able to reprogram it it has 170000 miles. can anyone help please ?

you cant just replace the PCM. its a paired unit with the immobilizer, which will also either need to be replaced with a new one, or the one out of the EXACT car in which you got the PCM.
then the keys will need to be reprogrammed.
so yeah, you're gonna need to bring it in.