Recently my 99 f250 super duty developed a miss,no check engine lights came on,but after hooking up a portable scan tool, I found a code . The code showed a misfire on cylinder 8. I changed the plug and coil pack ,but I still have the miss.I then pulled the plug wire and hooked to a new plug and could see a good spark. The scanner still shows a miss on #8. Anybody have any ideas?