you can unplug the harness and check the resistance of each injector. if one is off, then you know it's bad. a simple ohm meter (volt meter) should do.Can you swap injectors? If the fouling moves to the other cylinder, the injector is bad. If it stays in that cylinder, you could try swapping plug wires with the cylinder that fires at the same time (1 and 4, 2 and 3). If it moves, bad plug wire, if it stays, you may have an oil control problem in that cylinder.