Ob2-ob1 Cel

I just finished pluging in my OBDI p13 ECU into my 2k Prelude. The thing is the car starts, but quickly triggers a CEL. I needed the car quickly so I reinstalled the stock ECU without checking the code. Anyone ever experience something like this? I thought this was a simple plug and play mod.

i did engine swap and put 01 engine in my 93 lude si and used conversion harness to use obd2 ecu w/ my obd1 harnesses. I know this is the opposite of what you did but i had no problems and as far as i understand it should be plug and play whichever direction you go. Id say put the p13 computer back in and see what code it is throwing