91 Mighty Max Truck running very rough. I have narrowed the problem down to an issue with cylinders 1 and 4. Cylinders 2 and 3 are firing properly. Getting spark, appears to be a fuel flow issue. Pulled injectors which appear fine and noticed 1 and 4 may be on the same circuit based on color of electrical connections. Looking at the wiring diagram it appears I could have an ECU issue going on. Any ideas appreciated? Where is the ECU on the 91 MMax? Can't get a straight answer from Haynes manual or Google searches.

Thx.