I'm with the guys who had problems with water and COP's. Every car I've owned I've been able to degrease and hose down the engine with zero problems- until the expedition. I found out the hard way last week that water and COP's don't mix. It was badly misfiring on several cylinders. Each time I figured out which one was bad, I'd pull the COP and it was soaking wet. The seals aren't that great on them. One of them was actually cracked on the plastic coil housing. I had a spare Accel, and a spare cheap one.
From now on I'll have to be much more careful, at least until all the coils are new.