2005 Mazda Tribute V6. Misfire in cylinder 4

2005 Mazda Tribute V6. Misfire in cylinder 4. Changed the coil packs and spark plugs, same problem. What is the voltage going into the coil pack? I measured 4.5 volts. On number 5 and 5 it read 14.27 volts. Can anyone tell me what my problem is??
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You could have a wiring issue to injector #4, or bad wiring/ground to the ECM, or a bad injector (NOID light would find that out), or even low compression in that one cylinder.