Hey guys, I saw in another post, a reference to AC3 and P4 ECUs. Could you explain what's the difference and how do I identify them.
Thanks for any info you can give, Jerry.
Basically, there are "families" of GM ECMs. There are a bunch of variations and lots of overlapping history, but to simplify:
- CCC - One of the first generations of GM ECMs. Used primarily as with a carb'ed application and adjusts a mixture control solenoid in the carb to control AF mixture. The easiest way to identify this ECM (in the car) is to look at the ALDL connector. The third pin from the left in the top row will be populated.
- C3 - the next generation of ECMs which were used for a variety of applications involving fuel injection. Everything from TBI to SFI and DIS (like our Buicks). It is a pretty neat little processor and surprisingly versatile. The easiest way to identify this ECM (in the car) is to look at the ALDL connector. The second pin from the left in the top row will be populated.
- P4/P6 - this is one of the last preOBDII ECMs fielded by GM and can be found in cars as early as 1988 and as late as 1995. These are more sophisticated in several aspects than a C3 and definitely have a faster datarate. The easiest way to identify this ECM (in the car) is to look at the ALDL connector. The rightmost pin from the bottome row will be populated.
- Hybrid - this was sort of an "in between" C3/P4 ECM that was used mostly in TPI motored cars (and some Holdens in Australia).
Again, that's kind a quick and dirty run down of the ECMs. It is by no means all inclusive or exhaustive, but in general that's what is being talked about.
Ken thanks for the quick and informative reply.
Jerry