I swapped out the 97 4.6 and put in one from a 1999 lincoln town car. I used my intake, timing cover, knock sensor, pulleys, etc. when i did. It has had pinging under a load every since. I took it to a ford dealer and they couldn't figure it out either. They said I could try using the intake from the town car because maybe the engine has higher compression and the truck intake is a high rise and flows differently than the car one. I don't know what to do so I thought I would ask any of you guys if you could offer some help. Also both engines are Romeos so they should be similar other than changes made between 1997 and 1999. I found out that the town car 4.6 has higher compression 10.1 compared to the 9:2.1 that came in the truck and what the computer is tuned for as well as the intake,maf sensor,throttle body, etc. is used to running with. With the higher compression of the car motor and the longer runner design of the truck intake as well as MAF sensor,egr etc. could it be causing my problems. It isn't pinging as much since the dealer looked at it but stumbles and misses if i give it too much gas quickly or out on the highway under a load. I have to just slow down a lot by letting off of it then gradually giving it gas again. It idles fine. Motor checked out fine. Someone has to have some suggestions out there? Im open to here from any of you with experience with these modular engines...Please!!!!