listen to the injector with a stethoscope and see if it clicking when running. It sure sounds like an injector or wiring issue. If the injector is not clicking, unplug it and (still running) take a test light and connect the ground to one wire and the test end to the other at the injector plug. Does it flash?
if not, the test the wires all the way to the connection where they all merge. Sometimes you loose the connection there and have to resolder.
Just because you have continuity does not mean a good connection.