Hi Guys, my '08 with 6.7L has been running great until about a week ago. After sitting a few days, I went to start it and the motor was running very rough, watching the voltage gauge fluctuate (assuming the grid heater finally had work to do, as temps got down in the 60s and 70s).

Drove the truck and it made power normally, but very choppy deceleration (revs came down like a sequential BOV, but but but) - was hard to start after shutting off.

FFWD two more days, went to start it and it started but ran very rough, so lopey it sounded like it wasn't firing on all cylinders - threw multiple DTC codes including MAP sensor, Fuel Rail Sensor, Crank, and Cam sensors, and low reference voltage to name a few.

I have seen people with this issue online, but to add to this I was getting full 30,000psi on my fuel rail gauge. at first, I suspected fueling issues but seeing max rail pressure didn't seem like it was short on fuel.

So I tried all of the typical troubleshooting things -

1. check battery voltage/ charge batteries
2. pull sensors and check for ~5v at plugs (getting around 4.95V)
3. clear codes and try starting
4. check connections on fuel rail sensor piggyback to gauge
5. inspect harness and plugs - look for shorted wires/ torn insulation
6. check grounds

I also tried unplugging the FCA (fuel regulator) and starting, which it did, and immediately I shut it off. Upon replugging, the first start the rail pressure read normal ~4000psi on the gauge and the truck fan fine - still threw all the codes though. A few more starts, running badly again.

Tried the same procedure, got it to run well, still all the codes. I can't be certain its an FCA issue - would that fail wide open sending max rail pressure? usually, it seems they fail closed and the truck starves for power.

Any thoughts? It seems the reference 5V voltage is an issue to these codes, people seem to have resolved by finding a short to ground, had a sensor finally fail, or replaced the batteries even though they didn't seem dead. Going to take the batteries for a load test later today and try to rule that out.

Any help would be appreciated - the truck is laid up until I can sort this out. FASS lift pump was making some noise so I am going to swap filters on that too just in case there is an issue back there.

FYI running a moderate RaceME Pro tune, currently on level 4.

Thanks

Eric