Engine began running rough, cleared up, back to running rough. Is missing on No. 1 cyl. Have replaced coil, module, plug, plug wire, compression balanced throughout @ 115psi. 220 cam w/1.65 rollers. Removed valve cover, good rocker action so cam appears OK. Replace injector on No. 1, no help. While cranking the engine over today I did get a loud backfire through the exhaust twice. Although I haven't readjusted them, the rockers don't appear to be too tight. Wondering if I may have a voltage problem to this one injector? Is there a proven way to confirm? Running a Fast system.