Originally Posted by
Turtle_au
You have narrowed it down to 3 possible issues
Oil Circuit shows Sump - Strainer - Pickup - Pump - Filters - Cooler - Engine
Oil Pump relief valve is between pump and filter and drains straight back to sump.
Oil Filter relief valve will bypass filter and send oil to cooler.
1. No oil getting to pump - blocked oil strainer, air leak in oil pickup ( maybe where pickup tube bolts to block )
2. Pump not pumping - drive failure, pump worn out, leaking seal or gasket.
3. Pump output not getting to filters - Pump relief valve stuck open.
Next step I would remove the oil pump relief valve housing completely. Disconnect the fuel solenoid wiring and crank the engine to see if you are getting oil there.