What happens is water gets between the cop boot and cylinder head this causes a short from the cop to the head this burns up the cop it then requires replacement. If you do decide to do this plan on putting at least a few cop's on it depending on mileage.

 

I have a 97 F150 4.6 Thought i would wash my engine bay out. bought the engine brite, pulled out the pressure washer and did the deed. After that could not go over 2000 rpm. come to find out your coil packs dont like to get wet. let them dry (7 days) still ended up having to buy new coils. so word to the wise save those wal-mart bags and cover up anything with a wire going to it