Fuel Systems & Fuel Delivery
Fuel pump operation, fuel injectors, fuel rail, fuel pressure regulation, intake manifold, and fuel system diagnostics including rich and lean conditions.
- Describe fuel pump function and the role of the check valve
- Explain fuel injector operation and the purpose of the fuel rail
- Identify MAF and IAT sensor functions in fuel calculations
- Diagnose rich and lean fuel mixture conditions
- Explain EVAP system components including charcoal canister and purge valve
Leçon 1
Fuel Pump, Filter & Fuel Rail Components
Fuel Delivery Overview
The fuel system delivers precisely metered fuel to the engine at the correct pressure. Modern fuel-injected engines use an electric fuel pump, fuel filter, fuel rail, fuel pressure regulator, and fuel injectors working together as an integrated system.
The Fuel Pump
The fuel pump functions to deliver fuel from the tank to the engine at the correct pressure. Most modern vehicles use an in-tank electric fuel pump that operates at 40-65 psi depending on the system type. The pump runs whenever the engine is running and briefly when the key is first turned to prime the system.
The Check Valve
The component that prevents fuel from flowing back to the tank is the check valve in the fuel pump. This one-way valve maintains residual fuel pressure in the lines after the engine is shut off, allowing for quick restarts without extended cranking.
The Fuel Rail
The fuel rail serves to distribute fuel to all injectors at equal pressure. It is a metal tube or casting that connects to each fuel injector and ensures consistent pressure across all cylinders. The fuel pressure regulator mounts to or near the fuel rail.
The Fuel Pressure Regulator
The fuel pressure regulator serves to maintain consistent fuel pressure to the injectors. It returns excess fuel to the tank to keep pressure steady regardless of engine load. Some modern systems use returnless fuel systems where the regulator is inside the fuel tank with the pump module.
Fuel Tank Rollover Valve
The fuel tank rollover valve serves to prevent fuel spillage if the vehicle rolls over. It is a gravity-activated valve in the fuel tank vent line that closes when the vehicle is not upright.
The fuel pump delivers fuel from tank to engine at correct pressure. The check valve prevents fuel from flowing back. The fuel rail distributes fuel equally to all injectors. The fuel pressure regulator maintains consistent pressure.