Objectives• Explain the difference between throttle body and port injection systems.• Describe the difference between a sequential fuel injection (SFI) system and a multi-port fuel injection (MFI) system.• Explain the design, purpose, and operation of major EFI components.
Objectives (Cont’d)• Describe the inputs used by the computer to control the idle air control and idle air control by-pass air motors.• Describe how the computer supplies the correct air/fuel ratio on a throttle body injection (TBI) system.
Objectives (Cont’d)• Explain how the clear flood mode operates on a TBI system.• Explain why manifold vacuum is connected to the pressure regulator in an MFI system.• Describe the operation of the pressure regulator in a returnless EFI system.
Objectives (Cont’d)• Describe the operation of the central injector and poppet nozzles in a central port injection (CPI) system.• Describe the operation of direct gasoline injection systems.
Types of Fuel Injection Systems• Throttle body injection (TBI)• Central port injection (CPI)• Port fuel injection (PFI)• Gasoline direct injection (GDI)
Basic Fuel Injection System• Input sensors – Give engine operating condition information to the computer.• Control module – Determines how much fuel the engine needs and controls the fuel injectors.• Fuel injectors – Meter and atomize the fuel entering the intake manifold or intake port.
Operating Modes• Open loop mode – The computer uses pre-programmed values and basic sensor information to determine injector pulse length.• Closed loop mode – In addition to the other input sensors, the computer uses signals from the exhaust oxygen sensor to determine injector pulse length.
Operating Modes (Cont’d)• Clear flood mode – The computer cuts off the fuel injectors when throttle position is high (wide open) and RPM is low (cranking speed).• Acceleration enrichment mode – The computer adds extra fuel during rapid changes in throttle position and manifold vacuum or air flow.
Port Firing Control• Multi-port injection (MPI) – The injectors are arranged and fired together in groups or pairs.• Sequential injection (SFI) – Each injector is fired individually just before the intake valve for that cylinder opens.
Gasoline Direct Injection (GDI) Features• Gasoline direction injection (GDI) – Allows for very lean air/fuel mixtures. – Increases volumetric efficiency. – Uses very high fuel pressures (typically between 400 and 1500 psi). – System operates similarly to diesel injection systems.
Summary• There are three types of electronic fuel injection systems: throttle body, port, and central multi-port.• Port injection systems use one of four firing systems: grounded single fire, grouped double fire, simultaneous double fire, or sequential fire.
Summary (Cont’d)• The airflow sensor determines the amount of air entering the engine.• The heart of the fuel injection system is the electronic control unit.• Two types of fuel injectors are currently in use: top feed and bottom feed.
Summary (Cont’d)• In a speed-density EFI system, the computer uses manifold pressure and engine rpm inputs to calculate the amount of air entering the engine.• In an EFI system, the computer supplies the proper air/fuel ratio by controlling injector pulse width.
Summary (Cont’d)• In an SFI system, each injector is controlled individually by the computer.• The pressure regulator maintains the specified fuel system pressure and returns excess fuel to the fuel tank.
Summary (Cont’d)• In a returnless fuel system, the pressure regulator and filter assembly is mounted with the fuel pump and gauge sending unit assembly in the fuel tank.• A central multi-port injection system has one central injector and a poppet nozzle in each intake port.
Summary (Cont’d)• GDI systems inject gasoline directly into the combustion chamber and allow for very lean operation.• EFI systems rely on inputs from various sensors; these include airflow, air temperature, mass airflow, manifold absolute pressure, oxygen, coolant temperature, and throttle position sensors.