[kitcarbp]

IF you have a check valve in the pump supply line that holds pressure after key-off, you can put a pressure gauge on the fuel rail and see how long it takes for the pressure to bleed down (within minutes or hours for leaking injector). If your fuel sysyem has a check-valve installed (usually part of the in-tank pump), your fuel rail should remain pressurized for several days. By seeing how fast the fuel rail pressure bleeds down will tell you if you have an injector(s) that are leaking. A leaking injector(s) symptom will also give excessive black smoke (rich) on start-up because of the fuel dribble from leaking injector into the intake runner(s), but once cleared of fuel runs great with no smoke. If you dont have a check valve in your fuel system, you'll have to confirm a leaking inj. by removing the injector and having it bench tested or swap in a know good one. This assumes you are confident the EFI harness for that injector is fault free (electrically its all sound). Make sure EFI ECU its triggering that injector correctly. I would also confirm you don't have an ignition issue on that plug wire or coil tower (or dist. cap terminal) to check the basics. You've ruled out the plug it seems, but ignition sys health upstream should be confirmed also.