The plugs aren't any different at all, they're functionally interchangeable. The binary data that's "burned" into the chip is the only difference. Don't put to much current through those plugs, 20vdc is enough to damage them. I believe that those chops are bipolar PROMs, high voltage will permanently "reprogram" them.
Date isn't important, the number will tell what combo you have. From what I've found:
M42 is a 22 (catalyst) or 23 (non-cat)
M40 is an 18
S14 is an 11
M21 is a 16
M20B25 uses 15 or 17 (non-cat?)
M20B27 is an 06
I believe there are different numbers for non-catalyst models too, and it's likely that there are different chips to reflect diff ratios. The fuel gauge is also different between the large and small fuel tank models. Any 4-cyl chip should work OK for you, of course the six-cyl chip would make your tach counter incorrect. Some really early E30 clusters have a different style code plug. It fits into a round port in the back instead of the square port in the front.
Topic: Cluster code plug (Read 3548 times)