Re: looking to purchase a tour van...need some advice..
The main thing is to see if it's been serviced properly. Some people just drive them and not pay attention to the services. The 5.4, 4.6 and 6.8 could blow spark plugs if they weren't done properly. If they're tightened too much, when the aluminum cylinder head expands, it pulls the threads. Our transit buses had no problem except for one that was tuned by a new guy that thought he knew everything. The 2004 5.4 didn't blow plugs but they could break when removing them. I changed them on my F150 and didn't break any. It had 80,000 miles. If they go too long, the get stuck and can break. There's also a special procedure to remove them. I still like them. Tunes aren't done that often and the rest of the time, there's no problem. Our Crown Vics with the 4.6 hardly ever had anything to fix with up to 150,000 when we replaced them. I bought one.