Will, a spark is not necessarily a "bad" thing. When you pulled on the harness and the connector came loose, the electrical connection was coming loose and current was still trying to flow to the injector. A spark (in that case) is current flowing through air and actually happens a lot more than most people think. Ever plug something into the wall that the on/off switch is in the on position and you get a spark before the plug is securely in the socket? It's the same principle. When you saw the spark, did it blow a fuse or pop the fusible link? Probably not, so I don't think it's a problem. I think you fixed the problem by securing the connection. And replacing the plug should fix it permanently.