Just a thought derived from experience with my car which once ran out of fuel because of a faulty fuel gauge, and would not start...
The car (not a FIAT) has an electric lift pump which is meant to move fuel up to the common rail injector system which is mounted on the engine, some way above the fuel tank, therefore the system needs to be primed if air gets into the lift system e.g. via air leaks on the suction side (or running out of fuel).
Priming simply consists of making sure the tank has several litres of fuel minimum, then turning on the ignition (this lifts fuel from the tank - you might hear the pump running, but it shuts off automatically to prevent damage to the mechanism) for about 10-15 seconds, then turning off the ignition for 20-seconds or so, the on again for 10-15 seconds, then off for 20 seconds, and repeat several times. If the priming works it will eventually fill the common rail system and the engine should fire
Let me know if this works...
Steve