Re: code 31 after gen 2 to gen3 ecu conversion
You haven't quite mentioned what was swapped in full.
As Falcon mentioned, did you swap the injectors (If not, you will run into problems running dangerously lean).
Did you swap the engine wiring harness? If not, did you change the Oxygen sensor from the single wire one on the original Gen 2, to the 4 wire that that Gen 3 uses? (If not, this is why your getting the code 21 error).
Not sure why your getting the 31 error. Have you tested the map sensor separately (Are you sure its not a dud)?
Whilst your at it, check base timing is set to 10 Degree's.
If you feel in a good mood, retard the exhaust Cam 5-10 Degrees too. (This is an instant 5-10hp on a Gen 2 engine)