Truck has low oil pressure at idle no knocks just low pressure

too low fuel octang, poor quality gas, or contaminated fuel, check fuel and igniton systems. Worn cam/crank/rod bearings, wristpins. Low oil pressure, so check your oil level.

Low pressure when at idle, after the engine has warmed up and the oil has thinned, indicates that the oil pump is worn and needs to be replaced.

sounds like lower engine damage, could be a bearing or low oil pressure but if knocking the damage is done. i would have a tech just double check it to make sure, i have seen flywheels make noise and pulleys and a/c compressors, so just make sure it is in the oil pan if so then engine will need repair.

It may be the oil pump. If the gauge is going up when the rpms increase it's probably not the gauge or pressure switch. If the computer senses the oil pressure is low it will shut the vehicle off to try to save it's self from catastrophic failure. Also it may start cranking longer before starting. Thats it building oil pressure before the computer will let it start. Make sure oil is full, clean & thick.

Low oil pressure will cause engine knocking at idle. Pressure climbs and properly lubes engine at higher RPM> Check your oil level.

Squealing may be caused by a loose/worn belt on the power steering system.

Before driving it anymore I would have someone test the actual oil pressure using a mechanical test gauge to see how much , or little, oil pressure you actually have. The knocking noise could be a hydraulic lifter that is partially collapsed due to low oil pressure or a rod bearing that has been damaged from low oil pressure. If it is just a lifter that is making noise then there's a pretty good chance that the lifter will quiet back down once the oil pressure is normal again. If it turns out that your oil pressure is normal both at an idle and at highway speeds then the noise may be unrelated. You can cause some serious damage by continuing to operate any engine that is low on oil pressure even if the dipstick shows it to be full of oil. Hope this helps and good luck!

after oil change' check oil pressure cold and then hot , then idle, if it goes up when reving it hot, thats good sort of,then if it goes way to low at idle and knocks, check idle speed. Fix it if so, still there , in the old days we would be cheap and put in a high flow oil pump, now I drive the "siht" out of a cheap car to see how long they last! It will supruse you> seen a 97 lumina with 400,000 km. slight knock and still going.

Does the oil light come on or the knock occur during the engine warm up after a cold start?
There could be a couple of problems causing the issue. You could have an oil pressure pump or pump pressure regulator sticking. I would have a mechanical oil pressure gauge installed and verify oil pressure at idle and 2500 rpms to make sure oil pressure is in normal ranges.
You could also have excessive piston rod bearing, crankshaft bearing or cam shaft bearing wear that will cause oil pressure to drop too low to prevent the rod knock your hearing at 2500 rpm.
You said a knock and not a ticking noise,so I don't believe a lifter is the issue at 2500 rpm.
Start with the oil pressure check and go from there.
Let me know.
Regards,

The engine is low on oil. but assuming it is not.
The engine is either idling to low .
The engine oil pressure itself is low. The engine oil pressure switch is leaking or not reading the oil pressure in the car.
I assume there is not knocking noise from the engine.
I would check for any oil leaks on the engine .
IF there are no leaks , I would change the oil pressure sesnor or switch first .
This could lead into major engine work.

Good luck

how low does the oil pressure drop?? is it below 40?