Coil Problems with ford 2002 350 super heavy duty van, Help needed!?!?

My father has a ford 2002 350 super heavy duty van and is having some coil problems. After he exceeds about 50m/h the car starts thumping and grumbling. I hear this is very common amongst ford vehicles, any suggestions? Anyone know the coil which it is so he can have it removed and fixed? PLEASE AND THANK YOU.