I screwed this piece out of under the oil filter housing. The probe at the end spins as if it's a tacho of some sort? Could it be the tacho for the revs? The engine is a 4bd1 turbo
Should have added the smaller piece with the probe screws into this piece below which in turn screws into the bottom of the filter housing
Not knowing a thing about that engine I'm thinking it is not a tach drive. Does that small part that you said turns have a ridge down one side the would pilot onto a slot down inside the part it screws into? Sorry if not really helpful but not seeing the parts in person I can only guess. I did try to look at some online books for that engine but could not find anything to be sure what it is.
Think its a oil pressure regulator valve. Guessing the top is removable and will have a thread and lock nut under it. The spinning of the pin might be adjusting the length of it and changing the preload on the spring.
There is a spring inside there alright which that spinning pin seems to go into. I'm looking for somewhere on this Isuzu 4bd1 tengine where I can put in a manual oil pressure gauge with a capillary tube.
1) t into the existing oil gauge lite 2) a mechanical tach drive did not exist that engine to my knoledge. Maybe a pulse generator on the alternator.