my 2005 5.4 has 115k miles. new plugs filters, fluids around 105k miles. it drives Perfect! almost.....once it hits overdrive at about 45MPH @ 1.2k RPM when i accelerate gradually the truck seems to misfire and has a major vibration/ bucks a bit. when i accelerate more it smooths out. I thought it may be the coils however a few days ago the vibration continued even when my foot was not on the gas pedal and i was coasting down the highway. at the time i was trailer a small utility trailer and atv. i drove it today and the issue is still there but much less noticeable

 

Have the MAF and throttle body been cleaned? I would eliminate those first, if they haven't. Also, were the boots replaced when the plugs were chanded and was dielectric grease used?

 

i used seafoam through the intake tube which i believe is after the MAF, dielectric grease was used and the boots were in great shape so they were re-used.

 

Seafoam is hard on the cats, use Techron in the future. There are witeups in the Aritcles and How To section on cleaning the MAF and throttle body. Check the index. I would do that first. At those miles, it will not be a waste of time.

One other thing you can check are the injectors for a leak. The 2005s had a known issue with injectors that started leaking. If you do have a leaking injector, I believe you will still be covered under the extended injector warranty letter. 120,000 miles or 11 years from date put in service.

 

What brand of plugs are in it?

 

This exact same problem happened with my 2006 5.4 however it would never do it when cruising down hill. Only when it was under a slight load, such as going up a hill or right before it would downshift to hit higher rpms. Had to replace my coils and good as new. However it has happened more than once so its a PITA

 

Don't put ANYTHING down the intake - put Techron in the gas. An exception is a BG or Motorvac treatment with the proper machine.

 

cleaned the air filter and maf. i also had the edge tuner on it and set it back to stock....not it hesitates even more under WOT. I got a oil change at the dealer about an hour ago and they immediately tried to sell the "3 valve tune up" which is nothing more than 8 spark plugs i told him i recently installed new plugs so he replied "well make an appointment for a diagnosis" ($98) for them to hook it up to their computer....needless to say i came back to the forums 1st

txsaltwater sounds like the same issue. to my knowledge they are the factory original coils. my 99 f10 had the stock coils until 210k miles but that truck was running bad regardless what rpm it was at....
i have a feeling this is my next step to look into. i would just think a bad ciol would set an engine code?

 

It won't set a code till the misfires reach a certain threshold. You can try to force it by holding it at the point where it's missing as long as you can.

Again, what brand plugs?

 

I'm chasing the same thing. I have the same year 05. That year had a recall Customer Satisfaction Program 07M08 injectors may stick open or closed you have 11 years or 120,000 just to give you some intel if you go to the dealership.
Mine has already expired. And I'm still chasing these problems. Don't fall for the Universal cat-backs either
Also a helpful post floating around.
https://www.f150online.com/forums/v8...ml#post5159499
Anyways hope this was helpful.

 

Did you put any dielectric grease when you installed the plugs?

You may have applied a liberal amount. It corrected the misfire issue with mine.

Do you know which cylinder is causing the misfire?

On a 5.4, it goes from Front of the vehicle to the rear.

Passenger-side bank = 1,2,3,4.
Driver-side bank = 5,6,7,8.

 

I finally got to have a mechanic check out the truck. apparently when connected to the computer it does not show any issues. he took it for a drive and said it definitely has a mis fire. so my mechanic said the issue is past the coils (because the computer shows all coils are working fine) and is most likely the plugs.

i just had a different mechanic do the plugs about a year ago if not more. that mechanic (1st time i used them) installed motorcraft plugs that I purchased (to know the right ones were installed) however unfortunately they do not warranty customer supplied parts

 

My truck had similar issue, bucking and surging only at certain RPM's. It was a misfire and sometimes it was so bad(like going up a hill) the check engine light would flash, meaning a real bad misfire.

Changed out the plugs with the OEM motorcrafts, runs like a champ now.

I'm betting that something happened to your plugs in the 10k miles they were in there, it sucks to do them again, but, good news is that since they are relatively new plugs in there, you should be able to get them all out without issues and breaking.

I'd do this job yourself!

 

If the mechanic that changed your plugs put too much antiseize on the shank, that can cause misfires. You might want to pull out the #1 cylinder plug (it's the easiest) and see how much, if any he put on there.
If you have access to a scan tool that reads fuel trims and/or O2 sensor data, you might be able to determine if one bank is running more rich than the other and focus your attention on that bank.

 

Only if he got antiseize on the ground strap or on the electrode.