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)
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.
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.
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.
