I have a 2002 5.4l and just replaced the engine. Almost done installing when I see a threaded hole the size of a nickel on inside of left head. Bought some block plugs to see if they fit. Anyone know if I'm missing a sensor or plug of some sort. I believe it goes all the way through.

 

On my 97 4.6 on the front of the drivers side under the intake, it has a CHT sensor, the 5.4s probably had one too.