ISX 12 code 4726 and 0559

[FarmLife]

I have a 2015 Peterbilt 365 with a Cummins ISX 12 CM2350 engine serial number 75035614. The truck has trouble starting and is smoking black. The rail pressure is bleeding off as soon as the engine stops cranking. I have capped off all the injectors at the fuel rail and it still loses pressure as soon as you stop cranking. I also noticed the lift pump is not working. If you supply the lift pump with 12 volts it works. There is only3.5 volts coming from the ecm. I tested the voltage at the pump connector and at the ecm. Both show 3.5 volts.

My next thought is to try running the engine with 12 volts supplied to the lift pump and see if that clears things up with the rail pressure. If it helps with the rail pressure I am thinking about swapping an ecm from another truck.

Any input would be appreciated.