1998 Mitsubishi Eclipse

Sam, I've done a lot of computer work over the years, but this a new one to me. The injector ground comes from a junction block below the relay box under the hood. This 12 volts feeds both #2 & #4 injectors. The power has to be good or you would have 2 dead injectors. The ground control for #4 injector (light green / red tracer) comes from terminal #15 on the engine control unit. This circuit has to be good, or you wouldn't have a pulse at all. I has to be in the ECM itself. Either a blown capacitor or diode. I've never seen this before, but then again, there's a lot of things I haven't seen. If I was in your position, I'd change the ECM. Hope this helps.

Sam, The plus voltage comes from a junction block under the relay box in the engine compartment terminal #15, blk/red wire according to the diagram. Also, #2 and #4 injector grounds are tied together somewhere in the circuit. Check continuity from #15 on the junction block to the blk/rd wires on injectors #2 & #4. Let me know what you find.