Sorry for thread revival, but you are in fact right about this thread being of use to someone in the future lol.
I've just done the same thing, put a u12 ecu into my d21 navara along with a pintara o2 sensor. The issues I'm having is trying to find an ecu pin out diagram for the stock d21 ecu. It seems impossible to find. On plugging my consult in and firing up nistune, i am getting a number of issues.
1. The power steering flag is on all the time; deactivates when a gear is selected (Neutral switch pin out is wrong?)
2. The start signal flag is on all the time unless you aren't idling (throttle valve switch pin out is wrong?)
3. AC pressure switch flag coming on whenever the steering is turned (power steering switch pin out is wrong?)
And finally, the o2 sensor is clearly functioning but I am basically using exactly the same amount of fuel as before (400km to 60 litres, highway driving)
Any of the hard body manuals I have found all have the same pin outs as defined in the u12 ford corsair fsm, yet on closer inspection and tracing these pins, the start signal with the d21 is in fact in the right spot, the air con switch is in the right spot, the power steering switch is in pin 44 when its pin 43 in the u12 fsm, and pin 44 is the Throttle Valve Switch Power Supply on the u12. However, pin 43 is a direct earth with the factory d21 ecu (Traced it to a screw and eyelet next to the ecu). So i could see why the power steering flag was always on as it was earthing as if the switch was active, so that pin definitely needs to be removed. Moved the power steering switch wire to its correct pin (43), confirmed it was in fact the power steering switch wire, but still no change apart from it not activating the ac flag, which was strange, seeing as that pin (44) is the Throttle Valve Switch Power Supply on the u12, which means that from the moment i plugged the ecu in and went to steer, it would've short circuited, as it would've opened an earth directly to the ecu's 8-10v Throttle Valve Switch output.. Checked that there was 8-10V as the fsm diagnostic describes, there was. Somehow. Confirmed that the neutral switch was in fact the right pin, so i have no idea why its triggering the wrong flags.
Maybe somehow it's fried circuits because of a different pin layout... thats what i wanted to know from day dot, is can i plug and play.. I'm anal when it comes to these things, i've done many successful conversions with rb's, ca's and so forth. I like to have everything working as per factory installation, pin for pin.
There is bugger all information to support such modification, or the fact that Australian d21's have a different pin layout. I really need a pinout for the aus spec d21, otherwise i'm going to pull out a loom of a wrecked d21, and reverse engineer that. I also spent many hours compiling a pinout document for the u12 ecu, all pinouts are correct and were compiled from the fsm. I just made a reference document like many other nissan engines have, but not the ka24e. I just need to work out the differences, as clearly there's something different between the two.