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?

The sender and/or gauge are probably bad. Most likely the sender. Could also be the wiring connector. Btw, starting it back up at operating temperature it should only have about 1.5-2bar of pressure at idle, not 3

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the reason it was 3 bar on restart is because it had only been running a few minutes between ons and offs and didn't get warmed up.

If it's the guage, that means the cluster has to be replaced. I've seen the back side of that guage at the junk yard and it's part of the whole thing.

That sending unit is in a tight spot and not much room to swing a wrench. I'm thinking of putting a "t" in there and adding a real pressure gauge so I wont panic at 70 mph when this thing shows 0 bar.