Hi, I'm trying to start an x300 that was almost totally disassembled for body work, hence the wiring has been removed and put back in and the engine rebuilt using many new parts.

Attempting to start it up for the first time we've run into a problem. Spraying starter fluid into the intake causes the engine to fire up and run for a brief period of 3-4 seconds before dieing. It will not start on its own, only emitting a brief sputter every once in a while while cranking.

The fuel pump is running, injectors are firing, and there is spark. I suspected the cam sensor might be installed the wrong way, so I tried re-setting it more than once, but still no change. I don't have a gauge to check fuel pressure, but fuel is gushing out the return line so I assume the pump is fine.

I'll be grateful if someone can point me in the right direction

 

You need to check the fuel pressure. Borrow or rent the gauge if you have to. The fuel gushing from return line does not mean you are getting the correct pressure at the rail. For example, if your fuel pressure regulator is stuck open, the fuel will get pumped in circles from the tank to the regulator and back. If the pressure in the rail is insufficient, the injectors will fire (the valves will open) but they won't spray enough fuel for the engine to run.