2002 Merury 115 EFI four stroke fuel delivery issue

I have a 2002 Mercury 115 EFI four stroke that has been stored since 2005. The fuel was drained, the lower unit lube was drained and replaced with new, the motor oil was drained, and the unit was located in a clean dry garage. I recently installed this motor on a boat and did all the routine maintenance including replacing the old oil filter, filling it with oil, draining all the residual fuel from everyoplace I could including the VST housing. There diodn't seem to be any gunk in the oil so I don't think that has anything to do with my problem. Once the motor was ready to fire, I pumped the bulb on the fuel line and turned the motor over a couple of times to get the whole fuel system primed. Unfortunately, it would never build any pressure in the fuel rail and therefore would not start. After rechecking everything about four times I decided to check my manual and see if I could get any hint about what I had going on. I found a troubleshooting page that stated to check both the + and negative side of the electrical connection on the fuel pump connection. When I did that I had 12 volts on the positive side but no ground on the ground side. I followed the troubleshooting steps further and hooked a wire from my battery + and - to the connection on the fuel pump and the pump began to pump fuel and actually built rail pressure up to the 40-50 psi range. Unfortunately, the motor still would not fire because the injectors would not fire. I suspect the same issue as the fuel pump; both of which suggest ECU. Since the ECU is quite expensive, I am wondering if there is any other reason the ECU would not run the fuel pump or fire the injectors? Any help will be appreciated.