My V10 was knocking when accelerating under 2000 rpm; rain and moisture made the problem worse. I discovered that the 2-part wiper cowl under the windshield allowed water to leak into the engine compartment and onto the throttle body, which then dripped onto the left side of the engine. This caused the spark plugs to rust and the 3 back ignition coils (coil on plug) on the driver's side to crack and fail. This caused a horrible misfire/knock that was worst under 2000 rpm especially in high gear and when the environment was wet. I fixed the misfire and cowling leak. Has not returned. I caulked the cowl and changed all my spark plugs and ignition coils. (roughly $300 for coils and changed them myself) I bought Denso OEM coils from carid.com for about $26 apiece. They did the trick, for a fraction of the price that the mechanic wanted($100 per coil).

 

I always try to carry a spare ignition coil in COP Fords. For some reason, Ford was having a lot of problems figuring COP out at that time. And ... Fords NEVER set a misfire code when a coil goes south.

 

I had two plugs and two coils go bad at the same time and my truck struggled to do 35 mph up any grade at all and it still didn't throw a code.

 

I had it happen when towing out in the middle of nowhere with no cell receiption for probably 50 or 60 miles. I found that the coil would work above 3000 RPM

So, made the whole trip going 55-60 in 3rd gear.