can i change the 4.6 to 5.4 in my 2008 f150 fx2
You can but you would need everything to make it run. You would need the trany to go with that motor, the computer and wiring harness for the engine, figure out a trany mount, may need a drive shaft, stuff like that.
I think you can swap out cranks and make your 4.6 a 5.4. The blocks are identical as far as I know. The 5.4 just has a longer stroke.
I suspect but don't know for sure that the swap would largely be bolt in with a correct for year 5.4. The engine computer would almost certainly need to be changed though.
Try checking a parts site for the part number for a new PCM for your 2008 4.6. Do the same for the 5.4 for the model year of that engine. If the part numbers are the same, you may be halfway home. If different, I suspect the pinouts will be completely different and you may even have more pinouts for the 5.4 than the 4.6. Then you will have to follow the suggestions made by the individuals above.
Looking for a Used F-150 in your area?
CarGurus has 10,010 nationwide F-150 listings starting at $2,900.
Search Ford F-150 Questions
Ford F-150 Experts
Related Models For Sale
Used Cars For Sale