electronic fuel injection overview autoshop 101

8/9/2019 Electronic Fuel Injection Overview Autoshop 101

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Electronic Fuel Injection Overview

How Electronic Fuel InjectionWorks

Electronic Fuel injection works on the somevery basic principles. The followingdiscussion broadly outlines how a basic orConvention Electronic Fuel Injection (EFI)

system operates.

The Electronic Fuel Injection system can bedivided into three: basic sub-systems. Theseare the fuel delivery system, air inductionsystem, and the electronic control system.

EFI #1 - SYSTEM OVERVIEW

© Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.



The Fuel Delivery System

• The fuel delivery system consists of thefuel tank, fuel pump, fuel filter, fuel deliverypipe (fuel rail), fuel injector, fuel pressureregulator, and fuel return pipe.

• Fuel is delivered from the tank to theinjector by means of an electric fuel pump.The pump is typically located in or near the

fuel tank. Contaminants are filtered out by ahigh capacity in line fuel filter.

• Fuel is maintained at a constant pressureby means of a fuel pressure regulator. Anyfuel which is not delivered to the intakemanifold by the injector is returned to thetank through a fuel return pipe.





The Air Induction System

• The air induction system consists of the aircleaner, air flow meter, throttle valve, airintake chamber, intake manifold runner,and intake valve.

• When the throttle valve is opened, air flowsthrough the air cleaner, through the air flowmeter (on L type systems), past the throttlevalve, and through a well tuned intakemanifold runner to the intake valve.

• Air delivered to the engine is a function ofdriver demand. As the throttle valve isopened further, more air is allowed to enterthe engine cylinders.

• Toyota engines use two different methodsto measure intake air volume. The L typeEFI system measures air flow directly byusing an air flow meter. The D type EFIsystem measures air flow indirectly by

monitoring the pressure in the intakemanifold.





Electronic Control System

• The electronic control system consists ofvarious engine sensors, Electronic ControlUnit (ECU), fuel injector assemblies, andrelated wiring.

• The ECU determines precisely how muchfuel needs to be delivered by the injector bymonitoring the engine sensors.

• The ECU turns the injectors on for aprecise amount of time, referred to as

injection pulse width or injection duration,to deliver the proper air/fuel ratio to theengine.





Basic System Operation

• Air enters the engine through the airinduction system where it is measured by

the air flow meter. As the air flows into thecylinder, fuel is mixed into the air by the fuelinjector.

• Fuel injectors are arranged in the intakemanifold behind each intake valve. Theinjectors are electrical solenoids which areoperated by the ECU.

• The ECU pulses the injector by switchingthe injector ground circuit on and off.

• When the injector is turned on, it opens,spraying atomized fuel at the back side ofthe intake valve.

• As fuel is sprayed into the intake airstream,it mixes with the incoming air and vaporizesdue to the low pressures in the intakemanifold. The ECU signals the injector todeliver just enough fuel to achieve an idealair/fuel ratio of 14.7:1, often referred to asstoichiometry.

• The precise amount of fuel delivered to theengine is a function of ECU control.

• The ECU determines the basic injectionquantity based upon measured intake air

volume and engine rpm.

• Depending on engine operating conditions,injection quantity will vary. The ECUmonitors variables such as coolanttemperature, engine speed, throttle angle,and exhaust oxygen content and makesinjection corrections which determine finalinjection quantity.





Advantages of EFI

Uniform Air/Fuel Mixture Distribution

Each cylinder has its own injector whichdelivers fuel directly to the intake valve. Thiseliminates the need for fuel to travel throughthe intake manifold, improving cylinder tocylinder distribution.

Highly Accurate Air/Fuel Ratio ControlThroughout All Engine Operating Conditions EFI supplies a continuously accurate air/fuelratio to the engine no matter what operatingconditions are encountered. This providesbetter driveability, fuel economy, andemissions control.

Superior Throttle Response and Power

By delivering fuel directly at the back of theintake valve, the intake manifold design canbe optimized to improve air velocity at theintake valve. This improves torque andthrottle response.

Excellent Fuel Economy WithImproved Emissions Control

Cold engine and wide open throttleenrichment can be reduced with an EFIengine because fuel puddling in the intakemanifold is not a problem. This results inbetter overall fuel economy and improvedemissions control.

Improved Cold EngineStartability and Operation

The combination of better fuel atomizationand injection directly at the intake valveimproves ability to start and run a coldengine.

Simpler Mechanics,Reduced Adjustment Sensitivity

The EFI system does not rely on any majoradjustments for cold enrichment or fuelmetering. Because the system ismechanically simple, maintenancerequirements are reduced.





EFI/TCCS System

With the introduction of the Toyota ComputerControl System (TCCS), the EFI system wentfrom a simple fuel control system to a fullyintegrated engine and emissionsmanagement system. Although the fueldelivery system operates the same asConventional EFI, the

Ignition Spark Management (ESA)

The EFI/'TCCS system regulates sparkadvance angle by monitoring engineoperating conditions, calculating theoptimum spark timing, and firing the spark

plug at the appropriate time.

Idle Speed Control (ISC)

The EFI/TCCS system regulates engine idlespeed by means of several different types ofECU controlled devices. The ECU monitorsengine operating conditions to determinewhich idle speed strategy to use.

TCCS Electronic Control Unit (ECU) alsocontrols ignition spark angle. Additionally,TCCS also regulates an Idle Speed Controldevice, an Exhaust Gas Recirculation (EGR)Vacuum Switching Valve and, depending onapplication, other engine related systems.

Exhaust Gas Recirculation (EGR)

The EFI/TCCS system regulates the periodsunder which EGR can be introduced to theengine. This control is accomplished throughthe use of an EGR Vacuum Switching Valve.

Other Engine Related Systems

In addition to the major systems justdescribed, the TCCS ECU often operates anElectronically Controlled Transmission(ECT), a Variable Induction System (T-VIS),the air conditioner compressor clutch, andthe turbocharger/supercharger.





Self Diagnosis System

A self diagnosis system is incorporated intoall TCCS Electronic Control Units (ECUs)and into some Conventional EFI systemECUs. A Conventional EFI engine equippedwith self diagnostics is a P7/EFI system.This diagnostic system uses a check enginewarning lamp in the combination meterwhich is capable of warning the driver whenspecific faults are detected in the enginecontrol system. The check engine light is

also capable of flashing a series ofdiagnosis codes to assist the technician introubleshooting these faults.

Summary

The Electronic Fuel Injection systemconsists of three basic subsystems.

• The electronic control system determinesbasic injection quantity based upon

electrical signals from the air flow meterand engine rpm.

• The fuel delivery system maintains aconstant fuel pressure on the injector. Thisallows the ECU to control the fuel injectionduration and deliver the appropriateamount of fuel for engine operatingconditions.

• The air induction system delivers air to theengine based on driver demand. Theair/fuel mixture is formed in the intakemanifold as air moves through the intakerunners.

The EFI system allows for improved engineperformance, better fuel economy, andimproved emissions control. Althoughtechnologically advanced, the EFI system is

mechanically simpler than other fuelmetering systems and requires very littlemaintenance or periodic adjustment.

• The Conventional EFI system only controlsfuel delivery and injection quantity. 'Meintroduction of EFI/TCCS added control OfElectronic Spark Advance, idle speed, EGR,and other related engine systems.

• Most of Toyota's late model EFI systems

are equipped with some type of on boarddiagnosis system. All TCCS systems areequipped with an advanced self diagnosissystem capable of monitoring manyimportant engine electrical circuits. Onlysome of the later productionConventional(P7) EFI engines areequipped with a self diagnosis system.

Reprinted with permission from Toyota Motor Sale,U.S.A., Inc. from #850 EFI Course Book.



electronic fuel injection overview autoshop 101

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