I have an '04 F150, 5.4l and it has been not running as good as it usually does. I pulled the #5 and #6 spark plugs but I don't know if I need to replace them. The plug on the right has about 2k on it while the left has about 20k miles on it.

 

Why do you have two different types of plug in your engine? I would replace them all with the same plug.

 

The #5 coil and plug had to be replaced a few months ago. Would you replace them because they are different or because the Motorcraft needs replacing?

 

The motorcraft plug looks like it has more than 20K on it... I would do them all with OEM and not run 2 types of plugs...