engine light came back on

My 2002 Mazda Tribute just had the #5 coil pack changed out. However, the engine light came back on shortly after it was fixed. It was the same cylinder misfiring. Any ideas on why the cylinder would be misfiring if their is a brand new coil pack. The

It has been back to the mechanic twice and now needs to go for a third time. No other codes but the code for a malfunctioning cylinder. New parts for the cylinder. What can be causing the misfire.

Love the site :-)