I have a 2010 f-150 5.4 v-8. I believe #4 (one closest to firewall in back on passenger side.).it seems like there's either dirt build up or something stopping the socket from going on the nut. it just spins. It's not loose. I can barely get a finger in there, but can feel it. I got a pic of it, it looks round like something is covering the nut. Any help would be appreciated. Not a mechanic.

 

Go read this thread in its entirety:

https://www.f150online.com/forums/v8...-solution.html

 

It is a lil curious that THAT plug seems to get more dirt buildup than others. SOMEtimes, you will see that it does not seem to be replaced, yet 7 other plugs have been. Take note. Read that other thread on this that was posted, carefully. 2 or 3 V imp notes in it.