Try checking the windsheild washer hoses . A hole in the right spot would definitely squirt fluid in there . Happened to me .

 

As canyonslicker said have someone operate the windsheild washers as you look under the hood you may not want the hood all the way up since the nozzles are in the hood but if there is a leaking line you should be able to see it. Assuming you have coolant in the radiator you should be able to rule that out by color. All you can do is look for any source of clear water close enough to drip or spray in that direction.

 

I know this is a super old one, but it still comes up as one of the first google results when searching this problem and I cannot believe that noone mentioned that this problem is almost always a bad intake manifold gasket. 40 bucks and a few hours wrenching and your problem is solved for another 100k. Hopefully before you destroy you cat trying all these other uninformed suggestions.

 

think that this issue could cause the #18 fuse under the hood to blow soon as the switch is turned to the on position? 2002 f-150 4.6 4×4

 

2002 4.6 doesn't use plug wires, it has coil on plug.