Hi there. I joined this site to see if anyone can help me with my issue I have had with my 04 f150 5.4 triton v8. I bought the truck with 115000 miles from a reputable dealer in town, super clean etc. drove it for 1 month (1000) miles. took it on first 3 hour trip out of town, and on my return whilst driving up a big hill I kicked it up to 70.....the truck lost power to about 60mph and the engine light flashed until I got to level ground and it stopped...I made it home the remaining 2 hours smooth driving apart from a little stutter when increasing speed.. (overtaking etc). I put it into a mechanic I have never used and they 'fixed' the issue for $2060! they replaced the cam phazer, both tensioners and solenoid. They said the timing chain had slipped and so I believed them....only drove the truck again a couple miles before taking my friends back to the airport 4 days later.....I left town 5 mins going 55mph and same issue happened on flat ground! took it back to same mechanic and left it for 2 days....turned out it was a coil pack ...total cost $233 which they did not charge me for...I feel like they wrongly diagnosed the problem but they insist they just overlooked the coil pack issue. sorry for the long post but I thought I see what you guys/girls on the forum think since you would know these trucks better than me....not mechanically gifted. thanks in advance. Mark

 

The engine light flashing means active misfire, I think a coil on plug is probably all you needed in the first place, but that is just my opinion.

 

You got your Cam Phasers and Tensioners replaced. These were the weak link on the early gen 5.4L motors. You basically got a brand new top end. This is a good thing but it was quite the expense. The COP experience is just as you describe it. When it firsts exhibits symptoms of a mis-fire they tend to occur between 45 and 55 mph. It may even feel like a transmission issue at first. You can get a set of COPs for $100 on ebay. Check out Global Automotive. They are super easy to replace. If I remember right it is an 8mm bolt that holds them in place. Get your self some di-electric grease before replacing them. Don't waste your money on anything but OEM replacements.
As for the timing chain slipping...it is completely possible and may be the result of using the incorrect viscosity oil. 5w-20 ONLY! Here is a link to a great article
explaining the issue in detail.
http://www.agcoauto.com/content/news/p2_articleid/115

 

There is no upside on spending 2 grand on parts that were not needed in the first place.