I am interested to find out if you solved the problem because I also have a 97 F250 and also live here in DFW.
The theory of the cam lobe going flat is very unlikely. It's a steel billet cam pushing a tiny flat piece that needs a lot less effort to push up than the lifters. Those lobes would go flat much faster than this one would.
I also don't think that you have a vacuum problem in the tank because if you poured half a tank of diesel and you only ran it for about 30 minutes and then the engine stopped, I don't think it would've built enough vacuum in the tank in 30 minutes to counter the suction of the pump.
Since you have already tried two different pumps and it is still doing the same thing, it is so obviously not the pump, so by elimination I think you have a restriction in the fuel line between the pump and the tanks that causes not enough fuel to flow at low RPM, and the engine burns it up faster than it flows, so the fuel bowl gradually empties. And only above a certain RPM, more fuel will flow than the engine needs to burn.
You could check this by installing a fuel pressure gauge in place of the Schrader valve at the fuel pressure regulator and seeing if the fuel pump holds pressure at, let's say, 2000 RPM and then let it idle and see if the pressure slowly decreases down to almost 0. If that is the case, blow shop air from the inlet of the fuel pump back thru the line by disconnecting the other end from the tank, and try to catch whatever comes out with a shop rag so that you know when you got it.
That's my two cents, or five. That's what I would do.
The theory of the cam lobe going flat is very unlikely. It's a steel billet cam pushing a tiny flat piece that needs a lot less effort to push up than the lifters. Those lobes would go flat much faster than this one would.
I also don't think that you have a vacuum problem in the tank because if you poured half a tank of diesel and you only ran it for about 30 minutes and then the engine stopped, I don't think it would've built enough vacuum in the tank in 30 minutes to counter the suction of the pump.
Since you have already tried two different pumps and it is still doing the same thing, it is so obviously not the pump, so by elimination I think you have a restriction in the fuel line between the pump and the tanks that causes not enough fuel to flow at low RPM, and the engine burns it up faster than it flows, so the fuel bowl gradually empties. And only above a certain RPM, more fuel will flow than the engine needs to burn.
You could check this by installing a fuel pressure gauge in place of the Schrader valve at the fuel pressure regulator and seeing if the fuel pump holds pressure at, let's say, 2000 RPM and then let it idle and see if the pressure slowly decreases down to almost 0. If that is the case, blow shop air from the inlet of the fuel pump back thru the line by disconnecting the other end from the tank, and try to catch whatever comes out with a shop rag so that you know when you got it.
That's my two cents, or five. That's what I would do.
