Jaguar Repair: low oil pressure, oil pressure switch, low oil pressure

Question
I purchased a 1986 XJ-6 4.2 that has low oil pressure. I placed a manual pressure gauge at the low pressure switch and found the pressure to be 7-10 lbs. I then started the motor with no gauge just open hole and found that the oil just trickled out and ran down the motor.So I pulled the pan and replaced the oil pump and cleaned out all the tubes and the outlet hole to pressure gauge.I also did the rod bearings while I had the bottom pan off. I did not do the mains. After assembly and start up the oil did squirt out of  the pressure switch hole approx. 2 feet. I then replaced the oil pressure switch but the pressure was the same, so I checked the oil pressure regulator valve and all seemed to be OK other than the o ring was hard so I replaced it, added a new spring and small piston and changed the transmitter and it seemed to increase just slightly maybe a couple of lbs. I still have very low oil pressure. Can you help? Thank you, Ernie-Tucson AZ.

Answer
Hi Ernie,
If you had the pressure relief valve out, did you also remove the filter block from the engine? Jaguar has several very different filter block designs and if the wrong gasket is used, you can have problems there. Also, you didn't say if any copper was showing on the rod bearings when you replaced them. If there was, you should have done the mains and used Plasti-gauge to check oil clearance on the mains and rods. Are you sure you used the correct oil filter?
Oil pressure is the direct result of the resistance of the oil to get through the bearings. A stuck open pressure regulator valve or loose bearing clearance is just about all that can cause low pressure. When you found the hardened "O" ring, did you check the gasket on the pipe to block?
Howard