Dynasys II crank no start

I just picked up a cascadia with the Dynasys II apu, a Caterpillar engine. The truck was completely out fuel I had to get fuel brought out and engine primed again, so I'm assuming the issue with the apu is that it needs primed. I'm not a mechanic and have no clue what I'm doing.

I opened the vent plug over the fuel water separator and let it crank a few times to no avail. When I turn knob on bottom the the separator fuel comes out.

Sometimes it starts and chokes out and dies after 3 seconds then will continue to crank but not start. Only error I get on the screen is engine start failure and to check connections and belt.

Trying to avoid down time to get it looked at anyone able to maybe point me in the right direction on this thing? Belt is tight has oil and coolant, I'm assuming good connection to battery ta just installed 4 brand batteries in here