My 97 has a obd1 conversion. With original key linked to immobilizer, Starts and runs.I've been wondering about the immobilizer - ecu relationship for awhile. The common theme has been that the ECU is tied to the chip in the keys...
I'm currently running a P28, and the green light's behavior has been unchanged since I swapped out my OBD2 ECU.
When the car was stock, there were a couple of times (2-3, tops) where the car would not crank over when I put the key in and cranked it. The green light would flash and as I understood from the owner's manual that was a "normal" mis-read of the key. Reinserting the key fixed the issue.
Recently I had a similar thing happen with the OBD1 ecu in the car. If my ECU was responsible for immobilizing the car, that result doens't make sense.
I'm tempted to see what would happen if I used an unchipped cut of my key to start the car.