My 2004 4.6L blew out a spark plug on cylinder #2 at 160,753 miles. Apparently this is an issue with the triton engines. Luckily, there's a kit made by recoil, part Number 98140T that is designed for the 4.6, 5.4, and 6.8 L triton engines. The kit is fairly straight forward to use. Total install time for the insert is about 2.5 hours. Then you have to let the RTV set for little while. After which, you can insert the spark plug and coil pack.

The crucial step is to ensure you're valves are closed so that the tap does not damage your valves while tapping the blown out spark plug hole for the insert.

Just wanted to provide a data point for anyone experiencing this problem.

 

Yep, there are a lot of threads about this. My 04 4.6 blew the #4 plug (closest to firewall on passenger side) and I had the fellers at http://blownoutsparkplug.com/ come out to my house and repair it in my driveway. I chose to have them do the repair as opposed to the other routes because they guarantee their work and will refund your money if the plug hole they repair blows out again.

From their FAQ:

 

The only do-it-yourself kit that is proven to work and to last is Time-Sert.

Too bad you didn't do some searching here before buying that kit, we have at least one member who rents a Time-Sert kit out.

 

That's interesting since the only modular motors that had that problem were built in the late 1990's. (In fact I believe the issue was fixed in 2000 or so.) The problem with those early motors was a design where only 3 threads held the plugs in. For a 2004 truck to blow a plug out, something else must have happened. I will offer that the fix would probably be the same though.

 

Actually, the early heads were 4 thread, and went to 8 thread in late 2003. The 8 thread heads have not been totally immune to blowout. With proper torque (28 ft/lb and *NO* antiseize), it's a non-issue, the factory torque spec of 15 ft/lb is way too low.