Yeah GM really messed with things in those years. Up to 94 things are simple, after 96 they are not that bad, but 94-95 can make you learn words that even soap won't wash out. What GM did was different than other companies, Ford for instance knew just like all of them that OBDII was going to be required in 96, so when they started on a design to be released in late 95 or 95 they built it with the full OBD II standard in place so it was already set to go.
GM on the other hand put together a few models that were intended to be new for 95 - up but instead of going to fully OBD II standard, they added some of the OBD II pieces to the existing OBD I system, then added additional electronics and hardware that makes them unique. Most mechanics who work on them call it OBD 1.5 and some other names I won't post! The problem is that you have to use a scan tool to work on them, and that scan tool has to run specific software to even work. They used two different ALDL connectors which only match the 95 model year first, then the software itself will not work with an OBD I scan tool, and most OBD II tools cannot read it either. Plus just to make it even more interesting, they didn't do this with every option package for a given vehicle. So you could get a 95 Chevy truck with say a 5.7 and automatic that was still OBD1 but a 4.3 version of the truck was OBD 1.5. Same in the cars, I have a couple cheat sheets from that time showing which ones do what but if at all possible I try to stay away from them because of the issues.
Personally if I had a nice earlier truck and wanted a modern engine I would probably do an LS swap with it's transmission, these days all of the mounts and such are available as kits along with a stand alone PCM that gets set up to feed the factory dash panel. It's a bit more work but once done you get a much improved vehicle. The other option is to build the 94 engine into something better, which can be done for a price.
Wednesday, June 9th, 2021 AT 2:00 PM