There is a technical service bulletin for the V8 engines regarding a possible problem with the spark plug being ejected from the cylinder head, damaging the threads in the spark plug hole. If the vehicle is under warranty, cylinder head replacement is recommended. If the vehicle is out of warranty, Ford authorized the use of a specific thread insert to repair the head.
Car Problem Reports
Ford F-350 Super Duty TSB For Possible Ejection of Spark Plug From Cylinder Head
Ford F-350 Super Duty Problem
Engines Affected: 5.4L V8, V8
Visitor, 2002 Ford F-350 Super Duty, 5.4L V8, 150,000 mi
blew out the spark plug so I tapped it again and used a helicoil