Make sure your spark plugs are tightened sufficiently. I do not know if the 2002 engine has the 5 thread or 9 thread holes but the Mfr. (Ford) torque rating of (I think) 17 Ft/# is insufficient to keep the plugs in.
When they go, they take the coils and possibly cyl. head with them. Take them out, clean/inspect and/or replace if necessary but tighten them properly.
Here is a link to a site that is run by a guy who makes his living (or at least part of it) repairing these engines if they have had this problem. His recommendations re: the preventative maintenance seem solid.
And another which "suggests" that Ford has authorized them for these types of repairs.
They are also known for having some issues with plug wires but I suspect that the later models had the coils connect directly to the plugs without the wires but JIC...
http://www.magnecor.com/magnecor1/cop/f ... 0.htm#pic1
As always, YMMV...but an ounce of prevention...as I tend to be proactive rather than listen to those who "have never had a problem so why mess with it" types. If it wasn't an issue, why is there a HUGE class action lawsuit out there re: this/these problems. If it were me, I would check it and fix it if necessary...and then enjoy the coach!