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.