2008 isx cummins not starting

Run a test line from the primer pump inlet to the fuel tank and see if draws fuel. If it does, either you have restriction in the trucks fuel lines or a hole so it is sucking air. If it still does not pump fuel, then you have a restriction at the engine or it is sucking air at the primer pump.

 

If you had a restriction the fuel isn't going to flow, so it is possible the filter would stay full. This would be a bad quick type of restriction usually caused by some sort of debris getting sucked up and blocking the fuel passage somewhere. A quick test would be just to remove the fuel filter at the engine and they turn the key on and let the primer pump run and see if there some fuel coming out. The main fuel pump fail and allow air to get sucked in at the pump housing. Are there any frame mounted filters on this?

 

No, I am not saying anything has failed yet. The filter on the frame is before the lift pump,(electrical priming pump that runs for 2 mins at key on). The filter at the engine is after the priming pump. If you remove the filter at the engine, then turn the key on, fuel should leak out of where the filter spins on. This fuel is being pumped from the electric priming pump. If you have fuel here, then everything should be ok from the tanks right up to this filter. It is unlikely there is a restriction is after this filter blocking fuel from the main fuel pump. So, if you have fuel leaking from there then I would say your main fuel pump has failed. It is common for the main pumps to fail, and when they do they suck air through their own housings. Either the pump housings crack, or gaskets fail, or whatever.