I was replacing my header gaskets on the 4.3 the other day, and on the driver side of the engine block there is a sensor that screws straight into the block and off of it is the plug. I was trying to get to one of the header bolts, so i went to unscrew it to get it out of my way. Little did I know that when I unbolted it from the engine block, massive amounts of liquid started to pour out of the side of the engine. It reeked of coolant, but was not did not appear to be the orange kind i use. It was somewhat dark in the engine bay but i made it out to be a light tint of blue or purple. It may have been the lighting in the garage. I was able to get the bolt back in very quickly and it seemed only about a quart or so of fluid came out. My question is, is this a knock sensor? Or maybe some type of coolant sensor?