Cummins N14 boosting the power/filter vac #'s

I'm thinking the blockage has to do with the fuel tank valves or sending units. This is what the gauge shows with the fuel filter plumbed straight into a Jerry can of diesel running at wide open throttle.

BTW, my no-start Issue was a fried fuse holder for the ECM. Yay road salt!

 

Frame mounted filter. I should probably retry this while hooked to the Davco.

This is the setup I rigged up to get those #'s.

 

O ring is good on there. For what it's worth I've discovered(on this truck) that when there is a leak at a fitting or one of the hoses(air in fuel) the #'s go down.

Rigged up the same set up running thru both filters and the #'s got no higher than 3".

Gotta be the tank valves or tank pickup sumps. Would make sense because every hose and fitting I've replaced so far have been jammed up with gritty black gunk.

 

Doesn't appear the vents are clogged, #'s still high with gas caps open.

Gonna see what happens with the back flush. I did notice more of the black gunk in the bottom of the Davco when I changed the last filter.