low oil pressure

[90 t4r]

ok to start off im a new 4runner owner just bought this truck (90 toyota 4runner with the v6) 3 weeks ago for next to nothing (cost me more for the taxes and title fees than the truck), it was at a mechanics shop and he was fixing to send it to the scrap yard because the owner hadnt been to pick it up in over 3 years, any way when i got it there was a knock that sounded like it was coming from under the valve covers, when i got it home i pulled the cover off the side it sounded like it was coming from but the cam and lifters looked and felt fine (no crazy movement) when i put it all back together i changed the oil in it and started it back up. it was still knocking but when i got the rpm up to lets say 3000 it would quiet down and stop and start back up when i let off the throttle, well after a couple times of doing this it actually stopped completely, but now there is NO oil pressure and it has hardly any power and wants to die if you try to rev it up. please help i am completely new to this and dont know were to begin, and im trying to fix me up a vehicle that i can use off road and in the snow, any help will b greatly appreciated