Freightliner M2 104 with an MBE900 will not start

I have a 2006 M2 with a mbe900 389ci the engine will not start at all. I thought at first it was a fuel problem because it would start and run from anywhere between 30 sec and one hour, it would than immediately die like the key was being shut off. I replaced the fuel pump, both fuel filters multiple times, replaced the fuel line, replaced the fuel line compression fittings, took the tank off and inspected it for problems, took off the fuel filter housings (bowls) to check for any hairline cracks, checked the air cleaner, put grease around the filter caps to prevent any air leaks, changed both the camshaft sensor and the crankshaft sensor. none of it fixed the problem. Now it will not crank at all and I have 70 psi fuel pressure at the when it did run and it will come up to 50 psi while cranking over. I think something is being triggered so the truck will not start, I checked the obvious... h20 sensor, oil sensors... all good. What is it that triggers an engine shutdown under normal conditions? Any help would be appreciated.