Opening the ECU and looking for the chip will usually do it, they aftermarket chips typically have a sticker marking the program on them. A stock P28 wouldn't make a B16A run rich, if even at all.

Don't fool with pressure regulators yet. All this can be solved with a dyno tune and an air/fuel controller, if you're willing to spend the money, however if you have some kind of "Spoon" or "Mugen" chip in your ECU, you need to get rid of it. They really wack out stock and lightly modified engines.