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DubTee

I recently bought a 2016 Peterbilt with a 734k mile isx15 demandated. I drove it twice and then picked it up and drove it 2.5 hours home, no issues. I got a new radiator, overhead, and full service on it, drove it 20 mins back to the yard where it sat for a couple days. I hooked up to my trailer and 20 mins down the road and into the loading facility the truck dies. I was able to fire it up, a little longer crank than normal but it fired up, not even 50 feet later it died again and would not start before draining the batteries. I haul hazmat tanker, and we are not allowed to mechanic inside the rack, so I had to be towed back to the yard. I ran some cables from my day cab over and let the truck charge for maybe 30 minutes while I look through codes using jpro (insite wouldnt connect via datalink) i mistakenly cleared them trying to see only what was still active but these remained active so thats where i started
spn 157 flash code 559 injector metering rail pressure - data valid but below normal operating range
spn 5585 flash code 4691 engine injector metering rail cranking pressure - data valid but below normal operating range

My initial thought being:
1. Low on fuel, must've pulled air from the lower tank
2. I killed the batteries to where the lift pump doesn't even have the ability to pull long enough to re-self-prime

Now fast forward to 2 days of research on the codes and possibilities of why it would've just died like that. I ran a high-pressure leak test. Truck got up to 28/29,000 psi, shut it off with both windows open and keyed back on and the pressure dropped very fast, down to nothing in less than 30 seconds. I reached out to a local mechanic and borrowed the leak test fitting for return flow. I got right at 200ml in 60 seconds with no injectors isolated. I removed fuel lines from injectors 4, 5, and 6 and capped them, I also torqued the injector connector nuts, these were torqued to spec. At idle the command pressure was around 7,000, killed the engine, key back on it fell fairly quickly. Re-install injector lines on 4-6 and remove 1-3 injector lines, torqued the connector nuts again (these were not torqued to spec especially cylinder 1), and capped at the fuel rail again. Idle, again the pressure was ~7000, killed the engine, key back on, pressure held steadily within 100 psi. Reinstalled all fuel lines.

With the injector flow return leak tester still installed from the fuel rail return i ran the high-pressure leak test, 30,000 psi check the return flow (looking for less than 200 ml in 60 seconds) I got maybe 40ml. So, I was happy with that. Still running at 30,000 for the flow return test I killed the engine and checked for pressure drop in 30 seconds, it held strong at 29,000 psi for a few minutes while i started picking up tools. I watched to couple more times after idling, killing it and keying back on and the pressure was not leaking off anymore.

I got on the interstate and ran the absolute sh*t out of it, and it did not miss a beat. I am going to assume this fixed my issue and I should be ok for a while. I will get 4 new batteries to ensure the voltage is correct and that it has enough to crank. I will also be inspecting the wire harness more closely because i have not ruled out the possibility of an electrical short that shut the engine down but for now i am content with injector connector nuts being loose as it is a common issue according to my research here and elsewhere. That could've easily been an injector job with one of these so-called mechanics. Saved my self a bit of money so i will now be ordering the test tools for my self!

Just wanted to share my experience and express a little gratitude for the gentlemen that help keep this site going, Hopefully i will be as helpful to others one day. (Reading @m*m^2 doc now)