spyderman

Replaced head gaskets on a customers car (leaking oil) a few months later the right cam plug came out and oil leaked out. We replaced engine with used part. Misfire codes flash at 5000rpm but is never felt. Replaced coil and wires. Switched plugs with 1 and 2 and switched 2 and 4 injector to determine if cause of misfire. Misfire stayed on 3 and 4. Misfire started after engine swap. I am thinking problem may be in trigger wire to ecm before main engine plug? Have been unable to locate wiring pin locations at plug.