As most people here have learned research of a product before purchase can be very beneficial. I own a 2001 F-150 and it has the 4.6 liter Triton V8. The 1997-2003 engines had spark plug problems related to minimal threading in the heads. This could allow the plugs to get loose and eventually blow out of the heads resulting in serious damage at times. There is a fix for said problem that involves a tool that re threads the head at about $200.00 per plug offered by most mechanics. Or you can purchase the repair kit yourself for about $250.00. The repair isn't too bad, but it is a pain to get to some of the rear plugs. Also the coil packs on these engines tend to fail in groups which can run around $80.00 a piece to replace. That can add up quickly. I think this is true of the 5.4 litter version of the Triton V8 of these years as well. It is true on the F-150's from 1997-present that the cab has to be lifted off the frame to replace the engine. That is a little crazy and can add some serious coin to what should be a simple engine swap.There may be another way to due an engine swap on these model trucks, but all the mechanics I've asked said the easiest way in the long run is to lift the body of the frame.
The 2004-2010 version of these engines have similar problems with the coil packs failing in groups, but I think they are a little less prone to having the spark plugs blow out. However they do have a weird two piece spark plug design that can be almost impossible not to break when trying to remove for replacement. The advantage of being able to run the newer spark plugs for more miles gets traded out by having them stuck and hard to remove when the times comes to replace them.
On a side note the E series vans that use the gas Triton engines have a slightly higher rate of coil pack failure due to moisture dropping down on the upper part of the engine during rain storms from the cowl drains becoming blocked or damaged. The water can puddle on the electrics under the hood and cause a coil pack to short out when you go to start one. My 2008 E-250 Service van as well as the two 1999 and the two 2010 model E-250 vans my former company owned were bad to go through coil packs. We averaged replacing all 8 per vehicle about every other year or so. These vans did get pretty heavy daily use, and some of the drivers were of the mind set of "Drive it Like You Stole it.":facepalm: Also we had one service van with a V10. What a piece of junk that was. I've been told to avoid the V10's if you can.
As for the 2011-present Triton V8's there is the two piece plug issue as well as the dreaded cam phaser problem. This is the reason I'm still driving an 01. When I have a problem with my truck I am fortunate to have a good friend who was a Ford mechanic for a local dealership that closed. He worked for them for 25 years, and when they closed he opened up his own garage. In the spring I had him repair a broken emissions exhaust line on my engine and I asked him straight up how much longer I should repair my truck versus replacing it. He looked my truck over and said he felt sure I had at lest another 100,000 miles left in her. She has 168,000 on her right now, and even though rust from road salt can be a problem for cars and trucks here in the mountains I do a "Thorough almost OCD" job of cleaning my under body after every winter weather event so she isn't rusted out. The other nice thing is she's paid for.
I asked him what he would buy if he were in the market for another truck and he said with the engine problems the newer Fords have, he had a hard time recommending them. He stated that Chevy and Dodge have their own problems that made them not too appealing either He stated the biggest issue with modern vehicles was the over abundance of computer controlled systems, and the cheap parts manufacturers have gone to to save in costs. I guess if you have a good vehicle that doesn't give you to much trouble your best bet is to maintain it as best you can, and do research on potential problems and their fixes prior to purchase.