Modern fuel pumps allow automobiles to operate at higher speeds and improve fuel economy in cooperation with a fuel injection system. Lift pumps add to that system by helping raise the level of fuel into the engine block by creating suction and managing air flow. These two distinct systems perform complementary functions in the fuel management system of an automobile, which is essential in newer high performance vehicles.
Lift Pump Functions
A lift pump functions to raise the level of fuel or other liquid up through a given system. In automobiles, the fuel lift pump works to build pressure or suction in the gas tank, thereby encouraging the fuel level to rise to the injection systems and on to the engine block. Lift pumps have several applications beyond automobiles and are also used in sewage systems to pump out waste from a full sump pump.
Fuel Pump Functions
A fuel pump is a mostly essential (older vehicle's use a gravity system to force fuel into the engine) component of an automobile's fuel system. Early versions of the fuel pump used mechanical elements to move fuel from the gas tank into the carburettor and then on to the engine, which worked primarily as a low pressure system. Modern fuel injection systems changed all that by electronically creating positive pressure from inside the fuel tank in order to force fuel through the system and into the engine block.
Lift pumps only assist in the raising of fuel levels in a given vehicle, they do not push fuel through the system. Modern fuel injection systems will have lift pumps installed with them as well, but will function without one as long as the fuel lines remain airtight, and the fuel injectors operational.
A vehicle will not operate with a non-working fuel pump, especially an electric one. Without a working fuel pump to push unspent fuel to the fuel injectors, a vehicle will simply not start. Replacement costs for electric fuel pumps can be double that of lift pumps, which is attributed to the more sophisticated construction of the fuel pump and the fact that a vehicle will not run without one.