Electronic Fuel Injection System (EFI)

Why modern car engines are computer controlled?

 Low exhaust emissions

 Good fuel economy
 Excellent driving performance under all driving conditions

EFI consists of a microprocessor based electronic control unit (ECU) and a large number of
electronic and electromechanical sensors and actuators. The following are jobs of this system to:

1. Provide accurate control of air fuel mixture ratio via fuel injection system
2. Assure accurate and precise ignition timing for all engine operating conditions
3. Monitor and control numerous additional parameters such as idle speed, exhaust gas
recirculation and air conditioner operation etc

What are the functions of electronic engine control systems (EECS)?

1. Fuel injection control

2. Ignition control
3. Idle speed control
4. Diagnostic function

What are component parts of electronic engine control system?

The engine control system is divided into three groups of components. These are

Sensors: record and transmit information in the form of electrical voltage signal to the ECU.

 Manifold pressure sensor: senses intake manifold pressure (D- type EFI).
 Air flow meter: senses intake air volume (L- type EFI).
 Crank angle sensor: senses crank angle.
 Engine speed sensor: senses engine speed.
 Water temperature sensor: senses coolant temperature.
 Intake air temperature sensor: senses intake air temperature.
 Throttle position sensor: senses throttle valve opening angle.
 Ignition switch: senses when IGSW is start position.
 Vehicle speed sensor: senses vehicle speed.
 Oxygen sensor: senses oxygen density in the exhaust gas.
 Neutral start switch: senses whether the transmission is in “P” or “N”.
 Taillight and defogger relays: senses electrical loads.
 Air conditioner: senses whether A/C is ON or OFF.
 Knock sensor: senses engine knocking.

Pr. By Aklilu Heyu

Engine computer: receives and processes the information contained from sensors and sends to
actuators for controlling the engine processes.

 ECU (electronic control unit): determines injection duration and timing, ignition
timing, idle speed etc… based upon the data stored in memory from sensors and sends
appropriate signal to actuators.

Actuators: receives the information from ECU and determines actual values of components.

 Injectors: injects fuel into intake manifold in accordance with signals from ECU.
 Igniter/power transistor: controls primary ignition circuit ON, OFF time.
 Idle speed control valve: controls idle speed by changing volume of air flowing through
throttle valve by pass in accordance with signals from engine computer.

The above electronic control system operates according to the IPO concepts. These means,

Input Process Output

Sensors ECU Actuators

TYPES OF INJECTIONS
Single-point injection (throttle body injection)
Single-point injection uses a single injector at the throttle body (the same location as was used by
carburetors). The earliest and simplest type of fuel injection, single-point simply replaces the
carburetor with one or two fuel-injector nozzles in the throttle body, which is the throat of the
engine’s air intake manifold. (fig. B)
Multi-point fuel injection
Multi-point fuel injection injects fuel into the intake ports just upstream of each cylinder's intake
valve. Multi-point fuel injection devotes a separate injector nozzle to each cylinder, right outside
its intake port, which is why the system is sometimes called port injection. (fig. A)

Pr. By Aklilu Heyu

Electronic fuel injection (EFI)

The electronic fuel injection system can be divided into three basic sub systems. These are the
 Fuel delivery system
 Air induction system
 Electronic control system

THE FUEL DELIVERY SYSTEM

Pr. By Aklilu Heyu

The fuel delivery system consists of the;
 Fuel tank
 Electrical fuel pump  Fuel injector
 Fuel filter  Fuel pressure regulator
 Fuel delivery pipe (fuel rail)  Fuel return pipe or line

Fuel is delivered from the tank to the injector by means of an electric fuel pump. The pump is
typically located in or near the fuel tank. Contaminants are filtered out by a high capacity inline
fuel filter.
Fuel is maintained at a constant pressure by means of a fuel pressure regulator. Any fuel which is
not delivered to the intake manifold by the injector is returned to the tank through a return pipe.

THE AIR INDUCTION SYSTEM

The air induction system consists of,

 Air cleaner  Air intake chamber
 Air flow meter  Intake manifold runner
 Throttle valve  Intake valve

When the throttle valve is opened air flows through air cleaner through the air flow meter (on L-
type EFI system) past the throttle valve and through a well tuned intake manifold runner to the
intake valve.
Air delivered to the engine is a function of driver demand. As the throttle valve is opened further,
more air is allowed to enter the engine cylinders.
EFI engines use two different methods to measures intake air volume. These methods are;
 The L- type EFI system
 The D- type EFI system
L-type EFI:

Pr. By Aklilu Heyu

  Measures the air flow directly by using an air flow meter.
D- type EFI:
 Measures air flow indirectly by monitoring the pressure in the intake manifold.

ELECTRONIC CONTROL SYSTEM

The electronic control system consists of ;

 Various engine sensors
 Electronic control unit (ECU)
 Fuel injector assemblies
 Wirings

The ECU determines precisely how much fuel needs to be delivered by the injector by
monitoring the engine sensors.
The ECU turns the injectors on for a precise amount of time, referred to as injection pulse width
or injection duration, to deliver the proper air/ fuel ratio to the engine.

Pr. By Aklilu Heyu

Self diagnosis system
This diagnostic system uses a check engine warning lamp in the combination meter (dash-board)
which is capable of warning the driver when specific faults are detected in the engine control
system. The check engine light is also capable of flashing a series of diagnosis codes to assist the
technician in troubleshooting these faults.

Whole system diagram for the electronic controlled engine

(This example is for the D-EFI type)

In the
electronic controlled engine system,
Sensors detect the state of the engine, and all information from the sensors is sent to
Engine Control Unit (ECU). According to the information from sensors, ECU calculates
injection volume and ignition timing. ECU also controls idle rotating speed by means of
the idle speed control valve (ISCV).

ECU gathers information from sensors about the engine, and then controls actuators for
Electronic Fuel Injection (EFI), Electronic Spark Advance (ESA) and Idle Speed
Control (ISC), according to that information.

And there is “SELF DIAGNOSIS” function in this system. If there is problem with the
electronic part of this system (that means, in the sensors, the wire harness and ECU itself)
The ECU detects the problem part and memorise it. When technicians check the “self
diagnosis code”, they can identify the problem easily.

Pr. By Aklilu Heyu