2004.5 5.9 Cummins. This happened during the 2020-2021 winter. I was idling for probably 30 minutes (yeah, not a great idea, but it was very cold and I had to drive to where I could check my emails). The engine has always been great for 155K miles, until this: it stumbled, missing a couple beats, seemed normal, but then it dropped several cylinders and stalled. When I got it started, it never got them all back. I headed for home (2 miles). It performed sporadically from 25 to 45 mph. I managed to back it into the shop (took everything it had). First, I totally disconnected the fueling box (was never using it, but it was suspect to me)..no difference. I will have to re-find the original codes it threw, but it trying to analyse the problem, I picked up others while checking injector harness(s), etc. I pulled the ECM and sent it off to be checked. Checked good. Was advised that the problem was a inj. harness so I bought 3 new OEM .Replaced them and adjusted the valves while in there. Got a sinking feeling when I ohm tested the old units....all passed. Just finished getting it back together and started it up....no better.
Now here's a weirdness that I am hoping will trigger one of your minds: It starts, sounds like it is running on 3 with NO power. Then at 12 seconds in, it goes to all 6 cyls. for about 1/2 second. it does that every 12 seconds until it warms up a bit when it just goes to running on 3 full time! There is virtually no response to throttle position.
It's got me totally stumped. I don't know what ro do next. Can anyone help? I will record the codes, which are many now.