Our engine will run on 5 cylinders once up. But on initial startup for the first time a handfull of things must be in line for kick over. It sounds like you have a leaking O ring and once you are pressurizing the system you are drowning out the plug and flooding the cylinder.
Check each cylinder for a small pool of fluid (fuel) and/or also for a very moisture soaked piston. That cylinder # will translate to which injector is most likely leaking.