A month ago I had no oil pressure when I started the engine. I opened the oil filler cap and could see oil flowing to the first cam lobe. So I knew I was getting some pressure. Went by a dealer and asked for the "old diesel expert" in the shop. He told me to jump the wire from the sending unit to ground and it would show a full 3 bar and I would know the sending unit was bad. It didn't. I put the wire back on and it has been reading normally until today and it quit again. I took a long pry bar type screw driver and used the handle part to tap on the sending unit, still no pressure. When I turned the engine off, I thought I saw a flicker on the gauge. I restarted the engine and had a full 3 bar as normal. So what's up? An intermittent short in the wiring, a gauge that's sticking or what?