hi taking a quick look at the wiring diagram for this system it looks like the mfu supplies the injectors coil pack and the o2 sensor heaters for both up and down steam sensors.
i would say its worth testing the supply from the mfu to above mentioned circits and the ecu grounds.
would also scope both the traces and the current for the coil pack to be sure the coil isn't kicking the ecu in the pants with a miss fire.
also current ramping the injectors to see what they are doing
hope this helps