ISX 12 code 4726 and 0559

[FarmLife]

I swapped a fuel rail relief valve with another truck. No change. Ran another fuel system leakage test. It will build pressure to 21,000psi. The commanded pressure gets up to 29,000psi but the measured will only build to 21,000psi. It still leaks all the pressure off as soon as you turn the engine off. I swapped an ecm from another truck and now the lift pump is working.

I think I am going to remove the high pressure pump head next.