I was goin to say it sounds like you have something just dumping oil back into the pan. If your not getting any psi like that.

How does a broken rocker arm cause no LPOP??? Do you have a lifter that is broken?

Is the key way on the crank for the lpop still there and good?

the broken rocker would have nothing to do with the pressure. if the key way is gone wouldn't that create a lot of metal particles in the front of the engine? that would put up a red flag to me.

The broken rocker arm would make it possible for the lifter to blow apart which would cause a large oil dump back into the pan and lower the pressure.

possible. i'm not going to agree or disagree with that because i'm not framiliar with th 7.3 to that extent.

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if the lifter blew apart, wouldn't there be some what big pieces of metal in the oil pan?

The inside parts of the lifter are no bigger than your pinkey and might not fall into the pan. They might land in the lifter galley right by the lifter body which should be in the lifter bore.

A broken rocker arm will simply not allow the valve to open and let the push rod do what ever it wants...

The lifter is held in with a keeper.

The lifter has a retainer holding it in the lifter bore and there is a clip holding the lifter parts inside it but when the rocker arm breaks I have seen many times that the pushrod bouncing around knocked the clip out and let the internal parts pop out of the lifter.

Thats possible I guess, but that would be a lifter issue, not a rocker issue...