So my room mate has a 2005 5.9L cummins dually and is experiencing a loss of fuel pressure when trying to gas it.. The truck still makes plenty of boost but just won't go anywhere because of a loss of fuel pressure. We put an Airdog 2 165, new injection pump, and a new fuel rail with valve. After spending 2,500$ we really need some help.

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Add randomly shutting off while driving to that list of things now

 

Injectors, FCA, COV, CP-3, batteries, grounds or wiring connections, take your pick. You need to do more digging to find the issue.

Run an injector return flow test, CP-3 return flow test, cylinder contribution test, validate actual rail pressure compared to commaned, validate fuel pressure to the CP-3 under all conditions. One of those tests is going to point you in the right direction.