2001 2500hd low oil pressure
 

I just replaced the oil pan gasket and now i have low to no oil pressure. any thing to check before i tear back into the engine to pull the pickup agin to see if the oring went bad.

thank you for you help
Jeremy

Sounds like you lost the prime in the pump when you dropped the pan.

how do you prime the oil pump?

There is a simple tool that can be purchased at most auto part stores. It is a simple steel shaft with an aluminum plate(looks like a big stepped washer) that fits into the hole where the distributor would go. The shaft engages the oil pump and the plate center's it in the hole. You connect the other end(end sticking out of block) to an electric drill. Set the drill to reverse and have at it. You will want to do it for about 5 or so minutes. Once done, remove the shaft and plate, restab your distributor, start her up and set timing.

i have never ever seen a chevy pump, unless assembled completely 100% dry not pick up oil. if the gears were wet, it will pick up. if you have SOME oil pressure obviously the pump is moving oil through it, which means its "primed". i would assume the pickup is sucking air. have you noticed the oil looking aerated (foamed) in the time that you ran it? that would definately indicate the pickup drawing in air.
priming the pump with a drill and the tool is no different than it spinning with the engine. if it wont pick up oil with the motor driving it, a drill isnt gonna do it any differently.

removing the pan drops the oil level to the same place as taking out the drain plug when you change your oil - you can not lose prime by doing that unless you dried out the pump gears with solvent of some sort.

This all sounds accurate. It is quite likely the oil pump pick-up got jarred when dropping or re-installing the pan. The pick-up may not now be low enough to stay submerged with the engine running OR the pick-up tube has been jarred loose where it presses into the pump body and air is getting in there. Drop the pan again and try to watch while doing so to see what likely interference there was or could be.

The procedure with the drill is what we used to pre-oil the engine before initial start after a rebuild.

put new oil pick up tube oring in and now no oil psi at all. what should i start to check.

jeremy.

also i pulled the oil psi sending unit and started the motor no oil came out. nothing!!!

You need to perform a oil pressure test with a mechanical gauge. Is there any chance the pick up screen was bent and is now touching the bottom of the pan.

no it was not touching bottom. pressure tested the pick up tube and held vacum. I am about to blow out the whole engine with air. and clean the pan agin. i dont know if there is any check valves or any thing that could be causing this.