Chapter Twenty-Eight Electronic Fuel Injection
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Chapter Twenty-Eight
Electronic Fuel Injection
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)
Port Fuel Injection
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.
Open and Closed Loop
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.
A Typical GDI System
Common Input Sensors
• Mass airflow (MAF) sensor• Intake air temperature (IAT) sensor• Manifold absolute pressure (MAP) sensor• Coolant temperature (ECT) sensor• Throttle position (TP) sensor• Crankshaft speed (CKP) sensor• Oxygen (HO2S) sensor
A Mass Airflow Sensor
A MAP Sensor
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.
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