I know, I know, this topic has been beat to death but I need to diagnose this problem quickly for a fleet truck at my work place and I don't have time to rummage through hundreds upon hundreds of different threads. We have an '08 F150 with the 5.4 3-valve engine and approximately 130,000 miles. It starts and runs great but after about half an hour of driving it will start running roughly. However, if you give it gas while it's running rough it clears out. I unplugged the VCT solenoids but doing so did not make a difference.

Also, can someone remind me if Ford fixed the two piece spark plug design by 2008? The truck has a constant misfire which is likely a C.O.P. and/or bad spark plug so I'd like to change them out eventually.

Any help would be greatly appreciated!

 

08 heads were supposed to be redone but when was it made . I can't tell you how to find out but some on here can .
If you use a tool like torque pro you can tell the raw data per cyl that is causing misfire . Requires android and blue tooth reader . Spark plugs were changed several times by mc . The older engines are running sp546's now .
Boots on plugs are a problem change them . They break down with heat oil and age .