* Lack of Fuel Supply: This is the most obvious reason. The engine needs diesel fuel to ignite and run. Without it, there's nothing to burn.
* Air in the Fuel System: When the tank runs dry, air can enter the fuel lines and injectors. This air disrupts the flow of fuel and prevents the engine from getting the necessary amount of diesel to operate. Air is incompressible, unlike diesel fuel, and prevents the fuel pump from working efficiently. The air needs to be purged from the system before the engine will start again.
* Fuel Pump Priming: Diesel engines often rely on fuel pumps to draw fuel from the tank and deliver it to the injectors under high pressure. These pumps may need to be primed (especially after being empty) to re-establish fuel flow. This often involves manually bleeding air from the system. Modern systems sometimes have electric pumps that handle this automatically, but they might require a few cranks to restart the process.
* Low Fuel Pressure: Even if there's fuel in the lines, if the fuel pressure is too low, the injectors won't atomize the fuel properly for efficient combustion. This can be due to the air in the system, a faulty fuel pump, or a clogged filter.
In short, running out of diesel isn't just about the absence of fuel; it creates a cascade of problems that need to be addressed before the engine will restart. The solution typically involves bleeding air from the fuel system, potentially checking the fuel filter, and possibly using a hand primer pump if the vehicle has one.
