Did you change transfer and HEUI pump? I'd check the sensor then. Unplug it so ECM defaults to run, see if it starts. If it starts swap sensors. If not pull and check the IAC valve for debris. Should make tone more pressure if the pumps are good

 

Most shops have a dead head IAC valve to install which will let you dead head the pump when cranking to prove the pump.That need to be done with a 4000 psi gauge installed in the head and then if the pressure is still showing low with the Et or reader your using then the pressure sensor or circuit is at fault.

 

Like I said I used a high pressure pump from an engine that is starting, so this is a known good pump.
I have et and a pressure guage attached to the oil manifold on the head and both are reading the same low oil actuation pressure. I even changed the oil and filter

 

The first 3126 that came out had a high pressure oil line on the injector that would crack some times and loose oil pressure. The next 3126 did not have the steel oil line to the injector.And also check the return fuel fitting in the rear of the head for metal in it.I have seen metal in them when the engine ran out of fuel and I guess if it was restricted it would not bleed the fuel system.

 

This one has the high pressure oil line attached to injectors, I have checked these lines and no leaks.

The fuel return fitting is good and fuel pressure is within specs

My main concern is the low actuation pressure because once low pressure the injectors will not atomize and this is what is preventing the engine from starting

 

Well its been years since I retired and I can not remember what the cranking hi pressure will read on that engine. I know it will run at idle about 800 but cant remember the crank pressure.Sorry I can help but do let us know what you find.