Mike: Might want to look at TSB 07-15-2. The 97-2003 4.6-5.4-6.8 used the 4-5 thread plug design. In 2003 the plug design was updated to 9-12 tread design on SOHC 2-valve mod. engines. The 3-valve 2004-at least 2007 had a totaly different but just as severe or... Login to read more.