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EVMV system E450 Super

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Keep getting a P0191 dtc after 100 mi drive or so.

Otherwise, engine seems to run fine, no suttering, no hesitancy on start etc.

But the fuel rail pressure sensor is expensive .

The only thing I can find wrong is that the evmv line from the vapor management valve to the engine looks soft and spongy at the curve in the line.The hose had a tag 9D289-CC, but this hose apparently does not exist at Ford, even though it is printed on a tag that says ford.  So I do not know how to replace it.  Could this hose collapse? would it cause a P0191?

Thanks for any help.

2006 Ford 6.8 V-10 on Class C   RV.

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The PCM (Powertrain Control Module) sends a signal , which is HALF of the duty cycle it wants, to the FPDM (Fuel Pump Driver Module) that supplies voltage to power the pump based on inputs from FRP (Fuel Rail Pressure sensor) to the PCM. More often than not, the FRP reads low for a given pump duty cycle and the PCM misinterprets it as a sensor issue, when it is in fact, the pump not outputting enough pressure. You need to check ACTUAL fuel pressure vs the sensor while the issue is occuring, remembering that the fuel pressure is referenced to manifold vacuum so it will differ from the gage. 

FWIW, it is usually the pump, high resistance in the FPDM ground, or, in the case of the same era F150, the case rotted open on the FPDM. 

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