From what I have read you can run the tt ecu & fuel pump with the na fpcu. You will only have 2 speeds but it will be fine. The na has 8 volts & battery volts, vs the tt which has 6, 7, & battery. So theoretically the na fpcu will be sending more fuel than the tt one at idle & part throttle & the same at full throttle. As long as you have a tt pump. That is where I am going to start.