93zstartedme

While chasing an opti problem with my 94z I swapped it's ICM/coil with the one from my 93z. I found out that there must be a difference between the two. Although both cars ran fine after the swap, once I got the 94 running again it had a code 42. I read a thread on the forum about someone else who had done the same thing and once they put the parts back on the original vehicles the 42 was fixed. I tried that and sure enough, the 94 fired right up with no codes. I didn't even have to pull the PCM fuse to reset things. I noticed that the 93 has one more wire on the black and grey connector that goes to the coil. I'm guessing that has something to do with it. Hopfully this could be an easy fix to all those who have swapped the 93 ICM/coil to a later model in attempts troubleshoot. If you tried this and got your original problem resolved you'll have a code 42 you probably didn't have until you put the 94 and later ICM/coil assy. back on. Just trying to squash a few more of those evil gremlins these LT1 motors seem to have.

Gaspo

i had the same problem. i bought a new distributor, cap, icm (ignition control module) and coil from someone off of a forum. they came off of their 93 trans am. i put it all back together and my car ran good but the SES light came on. i seemed to be using a lot of gas. i scanned it and got the code 42. what i did was switched the old icm with the new one and the code went away. i used the coil from the 93 and i havent had any problems, so it must just the the icm. good luck!

shoebox

The additional wire on the 93 coil plug is for the tach. Later years took the tach signal from the PCM, instead. That is why it is empty on the later models. Other than that, the coil/ICM wiring circuits between 93 and 94-95 are identical.