I changed my plugs today with Motorcraft plugs. 4.6L one piece plug is a much easier chore than the older 5.4's.

I really could have waited as I have 92K on the clock and the plugs looked amazingly awesome. No misfiring or any symptoms, i just figured that I would be proactive.

Next time I'll examine the first one that I remove and make a decision whether or not to continue.

 

There is no guarantee that the next 7 will look the same as the first one. You will have to remove and inspect all of them if you want to be sure.

A couple of months back I had a misfire in my Mustang. I figured I'd start with the plugs since they were about 4 years old. Every plug looked perfect until I got to the 8th one. It had carbon build-up on it to the point of having bridged the gap between the electrodes. With the 8 new plugs installed the misfire was gone. Now if I had stopped after the first one because it looked good, I would've wasted a lot of time trying to track down the problem elsewhere. The moral is assume nothing and double check everything.

 

The 2004 expys did not have the two piece plug, that came with the 3valves for 2005.

 

Yeah, I know. It was more of a celebratory statement.