I own a 2003 Expedition. It was my close friends who passed away. It's an XLT with 4x4 and the 5.4L engine. I heard the 5.4 was trash, not to waste time or money on performance parts. Just get a 351 block and start there. Only problem is the electronics and how it would work with the 4x4 drive. I don't assume they make an OEM computer for a 351 with automatic 4 wheel drive... Or do they? How could I get the computer to work for both the engine and transmission/transfer case???

 

There is a lot of work involved in what you are considering.
If you have unlimited funds and time AND facilities to do what you are contemplating , you can only hope it will even start.
A lot will depend on the condition of the vehicle and the degree of good maintenance it received. You might come out ahead with staying with what you have and providing regular good maintenance. A little tip,,don't believe everything you hear !
After you are done reengineering the powertrain, you can move on to the trans which is closely regulated to info reported by the 5.4, Still think you want to get involved with that.?

 

The SUV has had regular maintenance done on it. It runs good. What started all this was it overheating immediately after I filled the coolant. I found the intake manifold where the intercooler connects was cracked and a piece was missing. So I found a used manifold and cleaned it up and got new gaskets but it was plastic like the old one. I wanted a metal intake so it wouldn't crack again since I planned on keeping it. However I couldn't get Edelbrock to reply to my email if their victor Jr series would mount right up...so I began looking up parts and I read about the spark plug threads being an issue and the intake of course but that's what made me think I wanted to swap it out and no I don't have unlimited funds or the time really or the facility. I think I'll stick with what I have and maybe add a few performance parts to the 5.4 as I go. I wanted it to have good torque since it is a 4x4. What's your opinion on performance enhancing parts I could swap out and things to ensure it's longevity?

 

The manufacturers spend a lot on research to , hopefully, provide a reasonable product that will with good regular service provide satisfactory service.

They can push the envelope for extra power , but there is a trade off as to just how much you can squeeze out of a stock engine without sacrificing longevity

There are a lot of products that promise the world and some do deliver, but we don't always know at what cost.
If you want a powerhouse that should last, that is what you should consider purchasing instead of trying to make one out of an engine that was not intended for that.
The manufacturers leave a safety factor so some get derrated and last longer, I believe you get the point.
You might consult with a speed shop who should be better able to answer a lot of your concerns.