My 1992 4D34-1AT3's injection pump is controlled by an ECU. It will start and run without it, but the drivability would be poor without it. It requires an ECU for any timing advance and additional fuel delivery under boost. I bought the FSM. That's what it says anyway.
I'll take some pictures this weekend and post up
I should have been more clear. The governor end of the injection pump is fully mechanical. All the 4D3's have the TICS setup for timing adjustments. There is no flywheel on the timing gear like the 4BD engines. FWIW, the UD FD46TA engines also use TICS pumps with mechanical governors. They actually look exactly like the Mitsu TICS pumps. The ECU you are talking about simply controls the TICS setup. It advances timing at startup and as RPMs increase.