It could be your fuel pump. On military rigs one way to check is to pump air in to the fuel tank to force air out of the lines and fuel to the injectors. Try that if you can figure a way to keep air from escaping the tank while filling it. If you do get it air tight, be carefull not to put to much psi in there as it will blow o rings. I wouldent go over 5 to 7 psi.