Fuel System Concepts

Basic Fuel System Concepts

• SFI (Sequential Fuel Injection) injects fuel sequentially into each cylinder
• PFI (Port Fuel Injection) injects fuel into the intake port before the intake valve
• GDI (Gasoline Direct Injection) injects fuel directly into the combustion chamber

CAFE Standards

• CAFE (Corporate Average Fuel Economy) are regulations that set fuel efficiency standards for vehicles, aiming to reduce fuel consumption and emissions

Fuel Composition and Types

• Gasoline is produced from crude oil through refining and distillation processes
• Crude oil is also used to make diesel, kerosene, jet fuel, lubricants, asphalt, and plastics
• Octane rating measures a fuel's ability to resist knocking during combustion
• E85 contains 85% ethanol and 15% gasoline
• Flex-fuel vehicles can operate using gasoline, E85, or a combination of both
• Top Tier gasoline includes enhanced detergents to minimize engine deposits

Fuel System Components & Functions

• A fuel composition test determines the ethanol content in fuel
• Placing the fuel pump in the gas tank reduces the risk of vapor lock and improves cooling
• Check balls in the fuel pump prevent backflow of fuel and maintain pressure
• Return style fuel systems use a fuel return line to send excess fuel back to the tank
• Returnless style fuel systems use a regulator or module to control fuel pressure without a return line
• Baffles in the fuel tank prevent fuel slosh, ensuring consistent fuel pickup
• A fuel pump inertia switch cuts fuel in the event of an accident, preventing fires

Fuel Pump & Injector Operation

• PWM (Pulse Width Modulation) manages fuel pump speed to adjust fuel pressure
• Fuel pump tests include pressure, volume, amperage draw, and flow tests
• Fuel injector operation relies on voltage creating an electromagnetic field that lifts the injector pintle, enabling fuel to spray
• The upper O-ring seals against fuel rail leaks
• The lower O-ring seals against intake manifold leaks
• Pulse width is the duration an injector stays open, measured in milliseconds
• One second equals 1,000 milliseconds
• The three ways to increase fuel delivery are increasing fuel pressure, enlarging injector size, and increasing pulse width
• The component moving fuel through the injector is the injector pintle or solenoid

Fuel Injection System Differences

• GDI (Gasoline Direct Injection) is the most common fuel injection system
• PFI injects fuel into the intake port, before the intake valve
• GDI injects fuel directly into the combustion chamber
• Compared to PFI, GDI increases efficiency and power but can lead to carbon buildup
• SFI injects fuel per cylinder in sequence, whereas MPI injects fuel simultaneously
• Fuel injector tests consist of resistance, balance, flow, voltage, and leakage tests
• PFI injector voltage typically operates at 12V
• GDI injector voltage is between 50V-300V because it's a high pressure system

High-Pressure GDI Systems

• Steel GDI fuel lines should be replaced and never reused due to the risk of leaks
• GDI systems utilize a low-pressure pump in the tank and a high-pressure pump on the engine
• GDI system fuel pressure can reach 2,000-3,000 psi
• Carbon buildup on intake valves can occur in GDI systems due to lack of fuel washing

Additional Fuel System Details

• The fuel pump runs for 2-5 seconds when the key is turned on to prime the system and pressurize fuel lines
• Fuel filters are directional and must be installed correctly for proper flow
• Fuel filter locations include in-line (under the vehicle), in-tank, or near the engine bay
• Noise dampeners/pulsators reduce fuel line vibrations and noise

Fuel Injector & PCM Control

• The amperage test for fuel pump requires wiring the meter in series with the pump and setting it to the appropriate amperage (A) setting
• Before removing a pressurized fuel injector, depressurize the fuel system
• A NOID light tests for the injector pulse from the PCM (Powertrain Control Module)
• The PCM controls the injector ground, pulsing ground to open the injector while power remains constant
• FPCM (Fuel Pump Control Module) controls fuel pump operation, pressure, and efficiency