Fuel pressure at idle??

[snailexpress]

(12-17-2017 )JMBT Wrote:  So I checked it with insite from a cold start this morning. It was 22 degrees out and the truck had been off for about 12 hrs. The measured rail pressure still showed 2800 psi. When I started it up cold, at a low idle 650rpms, commanded was around 5800 and measured fluctuated by 1200psi. 5000-6200 After fully warmed up and running down the road a bit, I parked and checked again. We were back up to 11900 commanded at idle, with measured still fluctuating by about 3000psi. 9900-13000.

Sound ok for a custom tune? Or too low at idle, maybe accounting for smoking after idling to warm up?? What about the fluctuation at idle of 3000 psi? Cummins says more then 1450 to replace it, but would that be different with a custom tune??

Definitely something is wrong in fuel system. If ECM commanded 11900 it should be close to this.
Start with fuel pressure sensor and it's wiring. also you can disconnect back flow tube from pressure relief valve and look if valve is leaking.