EFI

#1 -  SYSTEM OVERVIEW

Electronic Fuel Injection Overview

How Electronic Fuel Injection

Works

The Electronic Fuel Injection system can be

Electronic Fuel injection works on the some

divided into three: basic sub-systems. These

very basic principles.  The following

are the fuel delivery system, air induction

discussion broadly outlines how a basic or

system, and the electronic control system.

Convention Electronic Fuel Injection (EFI)

system operates.

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EFI #1 -  SYSTEM OVERVIEW

The Fuel Delivery System

•  The fuel delivery system consists of the

fuel tank, fuel pump, fuel filter, fuel delivery

pipe (fuel rail), fuel injector, fuel pressure

regulator, and fuel return pipe.

•  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 in line 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 fuel return pipe.

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EFI #1 -  SYSTEM OVERVIEW

The Air Induction System

•  Air delivered to the engine is a function of

•  The air induction system consists of the air

driver demand. As the throttle valve is

cleaner, air flow meter, throttle valve, air

opened further, more air is allowed to enter

intake chamber, intake manifold runner,

the engine cylinders.

and intake valve.

•  Toyota engines use two different methods

•  When the throttle valve is opened, air flows

to measure intake air volume. The L type

through the air cleaner, through the air flow

EFI system measures air flow directly by

meter (on L type systems), past the throttle

using an air flow meter. The D type EFI

valve, and through a well tuned intake

system measures air flow indirectly by

manifold runner to the intake valve.

monitoring the pressure in the intake

manifold.

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EFI #1 -  SYSTEM OVERVIEW

Electronic Control System

•  The electronic control system consists of

various engine sensors, Electronic Control

Unit (ECU), fuel injector assemblies, and

related wiring.

•  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.

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EFI #1 -  SYSTEM OVERVIEW

Basic System Operation

•  As fuel is sprayed into the intake airstream,

•  Air enters the engine through the air

it mixes with the incoming air and vaporizes

induction system where it is measured by

due to the low pressures in the intake

the air flow meter. As the air flows into the

manifold. The ECU signals the injector to

cylinder, fuel is mixed into the air by the fuel

deliver just enough fuel to achieve an ideal

injector.

air/fuel ratio of 14.7:1, often referred to as

stoichiometry.

•  Fuel injectors are arranged in the intake

manifold behind each intake valve. The

•  The precise amount of fuel delivered to the

injectors are electrical solenoids which are

engine is a function of ECU control.

operated by the ECU.

•  The ECU determines the basic injection

•  The ECU pulses the injector by switching

quantity based upon measured intake air

the injector ground circuit on and off.

volume and engine rpm.

•  When the injector is turned on, it opens,

•  Depending on engine operating conditions,

spraying atomized fuel at the back side of

injection quantity will vary. The ECU

the intake valve.

monitors variables such as coolant

temperature, engine speed, throttle angle,

and exhaust oxygen content and makes

injection corrections which determine final

injection quantity.

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