Fuel injector system not responding

[roger429]

I have a 1989 Jeep Cherokee Pioneer 4x4 AT 4.0L MPI 4 door. Problem: the vehicle will not start; but, if I put fuel in the air horn/throttle body the vehicle starts and runs great until the fuel runs out. Apparently I'm bypassing the fuel injection system by putting the fuel in the throttle body. My diagnosis is the fuel injectors are not firing. But why?
I have tested and cleaned all 6 injectors, put new o-rings on each end of all injectors, cleaned the rail inside and out, replaced both quick-connects--fuel line to rail and return line to fuel pressure regulator, checked the fuel pump pressure--at spec, have a new speed sensor and distributor, and new spark plugs. Since all of the injectors are not opening it might be a bad ground, but where do I look to find where that ground wire bundle is actually grounded. At the computer? On the block somewhere? In the wiring bundle itself--which doesn't seem possible since all injectors are affected.
I'd be happy to hear from anybody with any idea as to what I can do to correct this matter, where to look, or what have you? Please.