This page discusses maintenance issues including the spark plug ones.
Spark plugs are a whole different animal on this engine. They decided to place each of these sensitive coils upon a specialized spark plug that tends to break when removed. Due to the design of the combustion cylinder, essentially these engines are semi-hemispherical, the plugs needed to protrude down through the head to the combustion chamber. The situation is slightly ironic since earlier 2 valve 5.4L (97-03) tended to blow spark plugs out of the head but later 3 valve 5.4L (04-07) tended to break off in the head.
These plugs generally last around 100k miles but they are a bear to remove when you do go to replace them. They have extended sleeves that reside down inside the head that tend to break off because of possible carbon/rust build up. This issue was fixed by a redesign of the spark plug in the 2008+ years. More details are available in another article I wrote which include step by step instructions on Replacing the spark plugs on the 5.4L Triton at home.
5.4 L Triton 3 valve engineI have already identified a mechanic who is familiar with the problems and has tools to deal with broken plugs. He says wait until the 100k miles before changing plugs.
