The document discusses electronic fuel injection systems and their components. It explains the differences between throttle body, port, and central port injection systems. The objectives are to describe the operation of major EFI components like fuel injectors, control modules, sensors that provide input on engine operation, and operating modes like open loop, closed loop, and clear flood. It also summarizes different types of port fuel injection firing systems and gasoline direct injection features and components.

1. Chapter Twenty-Eight
Electronic Fuel Injection

2. 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.

3. 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.

4. 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.

5. 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.

6. Types of Fuel Injection Systems
• Throttle body injection (TBI)
• Central port injection (CPI)
• Port fuel injection (PFI)
• Gasoline direct injection (GDI)

7. Port Fuel Injection

8. 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.

9. 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.

10. 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.

11. Open and Closed Loop

12. 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.

13. 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.

14. A Typical GDI System

15. 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

16. A Mass Airflow Sensor

17. A MAP Sensor

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.