These guys have some great info, mach-1-morgan. We did redesign the heads back in 07 and the issue was taken care of. You can PM me with your dealer’s name and order number when you place your 2013 order, so I can help you track it. Have a good one!

Deysha

 

I have to get that thing running again! And I recommended running a high octane with a injector cleaner 1 week before you pull them out. Then before you do it run a seafoam treatment and drive about 10-15 miles for it to clear all out.
Then loosen the plugs a hair and let it sit all night with tranny fluid in the spark plug holes. Helps to loosen them up.

 

Here's the TSB. The procedure for the 4.6 is the same as the 5.4L.

https://themustangsource.com/attachm...sb08-01-09.pdf

 

Ok I do these things all day first think is to get either ford carb tune up or gm top engine cleaner basically the same stuff and a spray bottle of water slowly pour the carb tune up down the thottle body while lightly spraying water till they are both gone while the engine is running than take a 3/8 impact gun to the plugs verry lightly Use the gun they come out almost every time Prob like 9 out of 10 times if you brake one use the Lyle tool the OTC ford tool sucks