what would cause the oil pressure to drop very low when the engine idles running on 1997 Ford F-150

its has around 40lbs at idle 2 or 3 lbs the engine has 125000 mile on it very will takin care of

Asked by for the 1997 Ford F-150
More info. on truck 97 F-150 aint enough! 5 engine possibilities, oil sae, what brand of filter. Is this a new problem?
Are you checking it with an actual test gauge?
Sorry its a 4.2 V6 Tried Changing the Filter and Oil I Use a 10/30 Quakerstate
That's ok noboy gives enough info. How are you testing the pressure?
remove the sending unit and installed a manual gauge sound like I can hear a knock like main bearings?
1 more answer , 2 more comments
I agree with wetry its hard enough to figure out problems if we dont have enough info
Thanks GG.
if you have knock then your oil pump might be gone you should get it checked before the engine blows