Much has been said and done with the modern fuel supply system, particularly the fuel pump. Today's supply pumps are usually in-tank mounted to provide good priming characteristics and reduce vapor lock. Fuel handling is improved as fuel is pushed directly from the tank.
Many systems are in use today, but they can all be divided into return and returnless.
The fuel then moves through a rail-mounted pressure regulator and back through a steel transfer line to the tank. Although this system has been used for years, it will more than likely go away as evaporative emissions requirements tighten. Fuel-return contributes to vapor formation, as any fuel flowing through a return system absorbs heat from the rail in the engine compartment. This fuel is allowed to depressurize in the return line and will raise the bulk fuel tank temperature. Returnless fuel delivery systems With tighter emissions standards, more of the 'returnless' fuel supply systems are being produced.