As said above, stroke valve maybe? The tractor I had would blow the O-Ring on the pressure relief valve. Took dealer long time to figure that one out. Did it several times. I could reach it on left side of tractor under the fuel tank from the rear. Took several extensions to reach it without taking tank out. I had to run engine fast to raise digger on the end. Maybe flow meter and pressure gauge to figure something out. Find "old timer IH mechanic" to help you out.