Truck will turn over but won't start

I am working on a 1996 Uhaul F-350 box truck, I replaced the complete distributor and coil along with plugs, wires, cap and rotor.
The ignition module itself was replaced, it still will not get any fire to the coil. There is power at the coil just no signal from the coil when cranking, also there is no data link established, we have tried multiple times at service shops and at home with diagnostics computers but they will not read it, I am being told that it may be an ecm issue?