Mike, Bill,
Thanks for all your help. Turns out Mike was the closest with his pinched wiring suggestion. Turns out that one of my wire ties had broken free at some point, and the harness was sitting on the exhaust manifold. The insulation on one of the wires had burned through (likely to injector #3), and the constant breaking and making of ground due to engine vibration made the injector act the way it did. I taped up the damage, and all runs well.