The oil pressure gauge has always worked. I recently changed my pcv valve and ever since my gauge will not work. If I tap on the instrument cluster the needle will jump around. Any ideas on what would be causing this? The engine is a 1986 lg4.

 

Check the connector and wire at the oil pressure sender. For your '86, I believe that's at the rear ledge of the block, just to the left of the distributor,

 

I checked the wire. Everything seemed to be connected right. Should I try replacing the oil sending unit?

 

Pull the wire off the sensor, touch it to a ground spot (bare metal on motor) and have someone watch the gauge for movement. If it does move the sensor is bad I'd guess.