changing timing chain
If your timing chain failed there has been damage to the engine internally. One of the best ways to tell is to do a compression test and compare the readings. If the pressures are very low on all cylinders than you have a problem. Timing Chain failures on the 4.6L and 5.4L engines are uncommon. What leads you to believe that?
Search Ford Expedition Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Ford Expedition Experts