I have a 99 f150 with a 4.6 liter w motor not original motor lost power computer showing blow by in 2 cylinders and a knock in another 1. Truck runs but runs rough had full tune up last year. Hoping I don't have to change motor but if I do what motors are interchangable

 

Unless the replacement motor is PI, you can use 1997-2001 non-PI.