Just wanted to share my experience...04 f350 6.0 w/160k:

"Check Gauge" light came on at idle...oil psi gauge reads 0.
Rev engine a little (2-500 rpm) and gauge comes back up (stock gauge).
Call a diesel mechanic buddy and run down the symptoms...he tells me to check the filter (since it is an easy check)...pull the cap and filter, and all looks good.

Drive to the dealer where diesel tech buddy works...they do an oil change, and still have the problem.

Removes the oil psi sending unit next to the filter housing, hook up a gauge, and reads <5psi at idle, 20psi at 1200rpm, and 30 psi at 1800 rpm (all are low per spec).

Pulls the check valve at the LPOP (again, easy check) and no problem.

At this time, he is thinking LPOP is failing, even though they rarely fail.

So, I drive away and take my truck to my regular mechanic.

They do all of the tests, and also note the oil is aerated...which makes them think LPOP pickup tube is cracked/broken...so they raise the back of the truck and over fill the oil....NO CHANGE...

So they are also thinking LPOP or Front Cover is cracked...take both off and both look great...they pressurize the oil passages and LPOP and no leaks...

Next, they drop the oil pan to manually inspect the LPOP pickup tube and it looks like new.

Finally, they remove the HPOP and there is a pressure release valve check ball and it is missing....apparently, this is very rare, and will allow enough oil to bypass the pump to show up as low oil pressure, and also let air into the system.

Thats my story.

 

dont know were you got the this is rare. its not. Any dealer tech that works on 6.0 should have knowen it. We see a few a month. Very few lpp pump issues happen unless a roller has come apart or an injector d-ring is broken and passes in to the g-rotor.
Now I hope you didnt go and buy a new pump. You can tap the hole were that ball was and incert a pipe plug. thats really not not a pressure relife valve it was made as part of the casting.
the pressure relife valve is the IPR

 

I've never had the pan off of a 6.0 but how are all these parts getting past the pick-up screen to get into the LPOP? What's the screen made out of, chain link fence?

 

chain link you say?

ya keep in mind they have to flow a large volume of 40w oil. what happens is a neddle bearing falls out of the roller and gets sucked threw the system and lands in the g-rotor. or a pice of the injector d-ring brakes off and the same happens.

but yes the screen will only keep out large objects I would say its about 1/16" chain link. think doll house size 1/24 scale chain link.