I have just replaced my oil pump again and I still have no oil pressure. But this time when I start it up after it has sat for a while I have great oil pressure, but when it idles down after about a minute the pressure drops right back down and the engine starts knocking.I did notice that the oil pump gasket that I had put on previous was on wrong and a piece of the gasket had broken off. It was a small piece about the size of half a pinky nail. Could this be part of the problem? Could I have a blockage somewhere? If so is there a way to flush out the engine? Im using 5w 30. Should I go to a heavier oil to help with pressure? Help me please.

91 Bronco 302

 

Would say you have either blockage or worn out bearings. Starting motor with pressure then after warm up pressure drops usually means bearings. only way I know to clean oil passages if blocked would be to rip block apart and vat it. I would run 10w-30 which ford recommends running.