It seems fairly clear that given the right number and type of sensors, the older MAF-based EJ18 ECU can run an EJ25 with a little richness, but nothing serious. I'm guessing that the two motors having such similar brake-specific outputs and fuel consumption helps a lot. A bunch of you have done this swap, but all I've seen so far are MAF-based setups, since that's all the USDM EJ18 ever got. Many other markets had phase II EJ18, (NA) EJ20 and EJ22 motors on into the MAP era.

I'm wondering how flexible the MAP system is in comparison to MAF...
I'm hoping that my stock ECU (MAP) can run an 00~03 EJ25 using it's sensors and injectors. Given that the injectors are already sized appropriately for the engine, might the EJ18 ECU be capable of keeping the fueling in range? Of course it might not be too hard to wire the 2.5 ECU into my car, but why go in there and hack the wiring harnesses if you don't need to?

A few places that might make life difficult, or might be a bonus:

My car has no EGR, and no second O2 sensor after the (single) cat. It also has none of that funky air-assist for the injectors. IAT sensor is built into the MAP sensor. It has a knock sensor, but no fuel tank pressure or temperature sensors etc.

Any ideas as to how this might work out?