I asked for some advice on this problem in the spring. Was hoping for some more input. My 930 has a freshly rebuilt motor and refurbished older style side mounted oil pump. The pump was bench tested before assembly. After 10 hours or so of successful operation it developed an interesting oil pressure problem that seems to come and go. Sometimes the oil pressure comes right up to 40psi within seconds of starting and is rock solid. Sometimes the oil pressure rises slowly to 20psi or less and jumps erraticly.The pressure can change 10psi or so in a second.
The behavior seems to correlate with temperature. @40f or below i"ve seen the jumping behavior and @30 or below a failure to generate pressure.
I"ve checked the gauge, changed the oil and filter without improvement.
One person suggested the pump could be sucking air but apart from the joint between the inlet screen there isn"t an obvious source for air..
Anyone in the Midwest have experience with these tractors at low temperatures? I"m assuming this is not typical. Anyone convert to the newer front driven oil pump? Wondering if that might be the way to go.

The oil pressure "jumpin around" have seen as a spun main bearing sometimes.

I agree take the line loose at pressure gauge watch flow, if you want to get scientific get a couple of glass measuring cups see how much you collect at different times. What about trying a different gauge?

Being that eradicate I would look for anything that can move. I do not think it has to do with tolerances. This would be the pressure relief on the pump, dirt in a gallery going to the pressure gauge. You might try taking the line off of the pressure gauge and putting end in the dipstick hole. Run tractor for a while to make sure line is flushed good. Any chance that a rag was left in the engine somewhere?