I bought a 48k JY 1999 5.9 engine in January and went to get it ready to start and cannot get oil pressure. not even a little. So here is what I have done:

Way back in March I swapped oil pans b/c oil one was rusty. Put 5 quarts in , took distributor drive out and used 5/16 hex on my big 1/2 hp drill clockwise to prime it. Never got pressure, but oil very VERY weakly oozed from lifters- no improvement even with turning engine. So i took oil filter off and put drill on and oil cam gushing out of the where the oil filter mounts, as it should. I figured it was air locked and would catch with my normal procedure for tough engines- overfill by 5 quarts and take plugs out and crank .

Did that yesterday and no reading on my mechanical gauge, which is working and accurate on my 88 and 93 trucks. So despite that I already inspected the pump pickup and distributor drive, I changed oil pumps figuring there must be a crack in the pickup I did not see. I tested old pump with drill- it pumped fine. I tested new pump- it was fine

I also hand turned engine before this and the camshaft is not broken. I put a new timing set on it and did not move cam or crank- keyways were perfect- no shearing. Engine sat in my barn in january and February but was buttoned up- no way could a mouse crawled into the galleys as the filter was on it the whole time

I called company and they sent me a video of the engine running before they pulled it and it was running and clearly shows 50 psi on the factory gauge.

I'm out of ideas and need help now. 2 pumps and 2 pickups would suggest its not a pump or bottoming out on the oil pan issue. Chnaged filters with no luck.

All suggestions welcome

stick a rod down the oil sender hole (port) at the top rear of the block & see how far down it goes to see where the diversion mini plug is (want 7&1/4" iirc). take the filter back off & blast some air in the top block sender port & see if you get air pressure at the filter boss port

Used a welding rod and plug is about 7 and 9/16 deep which is in spec.

Yes there is some leeway on the distance. I'd blast some air in the sender hole & see if the passage out to the filter is open. You have psi out to the filter & all that is left is the upper horizontle passage back to the vertical gallery (above the cup).

Full air flow from sendèr hole to oil filter boss

Just got it. Had to crank for very long time but gauge shows pressure. Thanks rapidrobert

thats good to hear & I went & measured & the "inbetween" section where the mini cup must go & it is an inch long & ~ a strong 7&1/4 to a strong 8&1/4" down from the top sender boss.