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...
58,000 original miles
Black on black
Never been wrecked (still has the stickers on all the body panels that say the VIN)
Perfect interior with the exception of a rough spot on the steering wheel
Some of the GO FAST Parts:
-D&D Performance Viperspec T-56 6-speed Transmission