What is the purpose of a fuel return line in an EFI system?

The purpose of a fuel return line in an Electronic Fuel Injection (EFI) system is to recirculate unused fuel back to the tank. This process helps to ensure that the fuel system has a consistent supply of fuel available for injection into the engine, while also preventing the fuel from becoming excessively hot or vaporizable due to prolonged pressure and heat in the fuel rail.

In an EFI system, fuel is pumped from the tank to the fuel rail and then injected into the engine. If the engine does not require all the fuel being delivered, the excess fuel must have a way to return to the tank instead of stagnating or being wasted. The return line carries this unused fuel back, which helps maintain optimal fuel pressure in the system and ensures efficient engine operation.

Additionally, it can help keep the fuel cool, as fuel that continually circulates can dissipate heat more effectively than stationary fuel. This design is crucial in maintaining engine performance and efficiency, particularly in maintaining the proper air-fuel mixture required for optimal combustion.