Hello, was hoping you may be able to answer a question for me.
I have a 2000 ford mustang gt with the 4.6 engine with 5 speed manual trans. The original 4.6 blew up on me I replaced it with one out of a 1996 gt with a 4.6 with auto trans. the car now runs at idle at 2200 rmp and wont rev down. it is showing a pcm trouble code. so my question is since I changed it to a 96 that was an auto trans and is now a manual and not the same engine that was in the car from the factory do I need to have the computer reprogrammed?
Thanks

 

Most likely the issue is that the 96 4.6 is not a PI 4.6. So it has the wrong heads, cam, and intake compared to what came in your car and what your pcm is programmed for.

 

Agreed with 1slow67, Even though its 4.6L there are variances in the engine like he discussed. PI heads non Pi heads. cams even slight differences on the intake. What trouble codes are you getting?