An electric energy fuel pump is used on engines with fuel injection to pump fuel from the gas tank to the injector device. The pump should bring the fuel under high pressure (typically 30 to 85 psi depending on the application) so the injectors can shower the fuel into the engine. When fuel pressure is within specifications, only then will the engine run correctly. Too little pressure can starve the engine for fuel, causing it to run lean, misfire, spatter, hesitate or stall. Too much fuel pressure can cause the engine to run rough, waste fuel (increase mpg) and pollute.