the ford spark plug thing is mainly limited to the 3V triton engine. most of these are 5.4L. although on all of their engines the passenger rear plugs are run under a heater line that is prone to leaking and rusting the plug in place. two seperate issues but same outcome either way. also some of the expeditions pay 4 hours to do the plugs. that's $450 plus 8 plugs at $10-15 each. this is why so many are for sale that need plugs. no one wants to put in that kind of money for a tune up with the possibility of a couple grand in head work as well. this is why the resale value is low. stay away from any ford suv with an eight. also the materials are crappy and expensive to replace. look at the lower radiator hose on most ford suvs and it's a multiple outlet hose with a quick connect fitting to the radiator. either shill out the money for a ford hose (around $100) or cobble it together only to have future problems. just one of many examples of how you could spend a lot of dough doing the most basic maintenance.
however i have allways wanted the furd fteenthousand
http://www.f150forum.com/f15/ferd-fteenthousand-80145/