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.

01-06-2018, From; Mike, I do not Know if the 4.6 ,3 valve & 5.4, 3 valve, are Easy to Exchange or Not, I know the Block's are the same as to the Bolt up to the transmission, I do Know the 5.4 Comes from the factory with a More Beefy ( TOUGH ) transmission due to the higher Take off power & Etc, I think I can Change my 5.4 ,3v , to a 4.6 3v, and use the 5.4 trans, Computer, wiring harness, I am planing to use all the 5.4 stuff, and just install the 4.6 Motor & hook every thing back up just like it was a 5.4 I was installing, the Firing Order is the same, the number of valve's are the same, So I am GONA GIVE IT A TRY , IF ANY ONE OUT THERE HAS TRIED THIS AND IT DID NOT WORK -PLEASE POST IT ,,with in the next few week's & I will Post how it turns Out.

How'd it go? I'm looking to do the same in my 2008 4.6L.