CRTC compatibility 88/89

[KDirk]

Wondering if anyone has swapped an 89 CRTC into an 88 (or vice versa) and noted any ill effects from doing so. They appear to be the same hardware internally, but definitely do have different PROM codes. Not sure what they would have changed between the two years that needed a firmware change.

I do wonder if the revised 89 CRTC PROM was related to the bogus fuel economy readouts on the 88 models. GM issued the 1988 ANCX ECM PROM which superseded the factory installed chip to correct this issue. I suspect the error in calculating the MPG's was actually in the CRTC firmware and since those ROM's were soldered in, it was easier to work around the error by updating the ECM PROM which could be swapped out readily; resulting in a sort of back door fix.

I've not dumped the ROMS from an 89 CRTC yet to compare the binaries to the 88 versions (which I have dumped for the purpose of modifying the program) but perhaps I will gain some insight after doing so.

KDirk