i pulled my 4.2 engine to rebuild it and when disconnecting the wiring connections i broke the end off this sensor. it is aluminum i believe on the right side of the engine block threaded into what seems to be a bolt that is tapped into the water jacket. i would guess it is a coolant temp sensor but i'm not sure so if anybody knows for sure what it is please post back and let me know so i can get it replaced...thanks

 

I believe you are correct.
Seem to remember the early 4.2 motors had 2 temp sensors and in 98 or 99, they went to a single sensor.

 

Could it be the anti-knock sensor?

 

i figured it out...it was a knock sensor...thanks

 

Oh well, I'm a day late and a dollar short.

I ran across my Haynes manual and thinking of this post, looked to find that in fact, it was a knock sensor you were asking about.

I wanted to let you know I was wrong in my prior post.