Knock on wood my 97 Expedition has never had a major problem. I had the plugs switched out at 100,000 with no problems at all. Im at 155,000 now and it is still running as strong as the day I picked it up 13 years ago! One of the most reliable vehicles Iv ever owned. Only thing Im gonna need looked at soon I think is the compressor for the air ride system its gotten a bit loud.

This was a known issue with the 5.4, and has been for some time.  You can go to the 5.4 gas motor forums on www.ford-trucks.com (Ford Truck Enthusiasts) and you can read all about the causes, as well as remedies, for the condition.  I don't remember all of the details, simply because I drive a Power Stroke, but you will be surprised at the wealth of knowledge you can find on those message boards if you are solution oriented and not there to bash Ford.  Just FYI.