The fuel pump relay is essential because it will keep power running to the fuel pump only when it needs to, which helps conserve fuel and keep wear down. The relay is essentially an electronic switch used to connect the fuel pump to the battery, which usually receives a steady 12- volt current. The relay switches on when you have the key in the ignition, and allows the pump to pressurize the fuel system to the factory pressure, usually 40–60 PSI on most vehicles. When the engine is running, the relay provides a continuous power supply, facilitating stable gasoline supply at different loads and speeds.
Because the relay is what controls when the pump runs, it also gives the pump the required protection against continuous running, which would run the risk of the pump over heating and reduce its life by as much as 30%. It can also cause a waste of fuel as the pump would circulate when the engine is not in need running all the time. The relay aids in preventing overheating for the very useful fuel pump, which remains on even when not needed by powering down when the engine is off or the fuel system has reached optimal pressure; especially important for those high-performance applications utilizing pumps running at over 100 PSI.
Other important function of the relay is that they are responsible for voltage stability when voltage drops down fuel can not be delivered to the engine. By limiting fluctuations in voltage, a properly functioning relay keeps the sensor and pump running optimally. A small reduction in voltage can decrease the effective pressure of the pump causing stalls or jerkiness, especially under load. Mechanics also recommend doing relay inspections regularly for vehicles that get driven a lot; this is primarily because, in case a relay fails, it can cause pump failure and the cost of replacing it is in the hundreds of dollars.
Replacing a defective or old Fuel Pump relay is inexpensive preventive maintenance that avoids bigger, costlier problems, by making sure that the pump works only when it should run and standards the vehicle performance and fuel economy, while improving the life of the pump.