Will it start if you unplug the connector from the FCA. I believe if you unplug this connector it will send rail pressure to the max but could help to rule out it as a cause.

 

I'm sure bout that I have done evrything, I took the rail sensor and limiting switch off another truck still no start. It's on the trailer now headed to dealer first thing in the morning.

 

What does your rail preasure read at key switched to on but not turning starter.

One guy had his reading high rail at key on without starting - (CP3) must turn to build p. So he had good idea of faulty rail p. guage. He changed rail guage and hard start prob went away. Mechanics are now leaning toward rail p. guage on my trruck that stalls ??? But they are trying to eliminate other problems first because we have been doing thee very exspensive change out parts diagnostic technique (stupid way).