where is the oil pump and how do i change it on 1999 Oldsmobile Aurora

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at start-up oil preasure is 72psi.when warm it will idle @15psi
(2) Answers
get a manual oil pressure check to verify.
if it is accurate, then you may have bearings that may have too much play. before you spend a lot of money on the pump, you need to be sure that the rest of the motor is in good shape. have a shop verify this for you first.