2006 KW t800 isx15 CM870 power loss

[ahrenb]

Where to start? I searched through and didn't find anything that sounded similar to my issue so I'm here to share and maybe someone has an idea that can help out.

Our oldest truck in our fleet is a 2006 KW with the isx15 cm870. When she is running, she's a workhorse, the driver loves her.

A few months ago, it started dying intermittently. At any sort of time, happened under a load on the highway at speed, happened sitting at the red light in regular traffic. Truck would just shut down out of nowhere. Check engine light would pop on but the only code would be "Power lost with ignition on" I thought I had it traced down to some bad battery cut-off switches. Changed them out with new and replaced the jumper wires on the batteries and the thing ran great for a few weeks. Came in for a service and found the charge air was bad, along with a slew of other minor issues.

We sent it out to our other location to repair as they had more room and time. It came back with the "all clear" from our other location. It had been used by a different driver when it was there for about a week and he reported no issues. The very first day that my driver was in it, he got about a half hour out and called me and said, "I just lost all of my power and am sitting on the shoulder of the offramp. Wait, it just died." So I went down there, computer in hand, and the only code it offered me, "Power lost with ignition on"

When this happens, it has a really hard time starting. Just seems to crank forever. I monitored the fuel pressure at key-on/engine-off and the rail pressure was about 20psi, when I got it running, rail pressure was in the neighborhood of 225-240.

We towed it back on one of our trailers and I just got hooked up to it again today. Started right up. Seems to idle a little low, around 550-600, which makes it seem like its running really rough. I warmed her up to 175*F and performed a cylinder cutout test, performed an injector test, performed egr valve and turbo actuator test, performed a cylinder contribution test. Everything came back fine.

I have to admit I'm at a loss. I'm of this newer generation of mechanics and if the computer isn't telling me what's wrong, I have a hard time diagnosing the issue. Any help would be much appreciated.

-Ahren