2004 Chevy Truck My injectors lock out and only fire on 4 c

I have a 04 chevy duramax deisel work truck. last week it broke down, going down the road and lost all power. The motor stated knocking, and the check engine light came on. The mechanic said the wire plugging on to the #1 cylinder injector was loose. This one wire being loose he says caused the computer to lock out all four injectors on that one side. Is this true? They cleaned the plug connections and cleared the computer. The truck ran fine for a week then last night quit again. I messed with the plug, but the motor would not run right until I filped the key on and off 5 times. Did I reset the computer? Why is my check engine light still on, the truck runs good for now? Should I replace the entire injector, or just the plug, I could not figure out how to detach the electrical recepticle from the injector body(not the plug with the wires connected to it but the peice on the engine)? I greatly apprechiate any help you can offer me, this simple problem is costing me alot of money.