Running out of gas is a much more serious problem than it used to be, because most vehicles are now fuel injected. This means that fuel is injected into the cylinders at high pressure through very small openings, which can be clogged by sediment in the fuel tank if the fuel level gets too low. First off, you need to relieve the pressure in the fuel system by allowing the air to escape from the fuel line. On top of the engine there is a pipe which runs all the way across the engine, which is called the fuel rail. At one end of this pipe there should be a valve of some kind, perhaps which looks like the valve on a tire. Opening this valve while the fuel pump is running will allow the trapped air to escape from the fuel line. Once gas begins to squirt out of the valve, close it, and crank the engine. If the vehicle does not start within 10 to 15 seconds, stop cranking the engine and let the starter rest for at least 2 minutes. Excessive cranking can burn the starter motor up. If repeated cranking will not start the engine, and there is fuel in the fuel rail, you may have clogged fuel injectors.