21.13_EFI ok

Diagnosis Master Technician - Gasoline Engine Control System EFI (Electronic Fuel Injection)- 1 -

2003 TOYOTA MOTOR CORPORATION. All right reserved.

EFI (Electronic Fuel Injection) Description

The EFI system uses various sensors to detect the engine condition and vehicle running condition. And the engine ECU calculates at the optimum fuel injection volume, and causes the injectors to inject the fuel. The figure shows the basic EFI configu-ration.

Engine ECUThis calculates the optimum fuel injection duration based on the sig-nals from the sensors.

Air flow meter or manifold pres-sure sensorThis detects the intake air mass or manifold pressure.

Crankshaft position sensorThis detects the crank angle and engine speed.

Camshaft position sensorThis detects the standard crank angle and the camshaft timing.

Water temperature sensorThis detects the coolant temperature.

Throttle position sensorThis detects the throttle valve open-ing angle.

Oxygen sensorThis detects the oxygen concentra-tion in the exhaust gas.

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Types of EFI

There are two types of EFI system clas-sified by the amount of the intake air detection method.

1. L-EFI (Air-flow control type)This type uses an air flow meter to detect the amount of the air flowing in the intake manifold.There are two types of detection methods: One directly measures the intake air mass, and one makes cor-rections based on the air volume.

2. D-EFI (Manifold pressure control type)This type measures the pressure in the intake manifold to detect the amount of the intake air using the intake air density.

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Engine ECU

Injector

Camshaft position sensor

Manifoldpressuresensor

Water temp. sensor

Throttle position sensor

Air flow meter

Oxygensensor

Oxygensensor

Crankshaft position sensor

Injection

Injection volumecontrol

Detectionof intakeair mass

Fuel

Injector

Engine speed

Engine

Air flow meter

Intake manifold

Air

Engine ECU

Injection

Injection volumecontrol

Detectionof intakemanifoldpressure Fuel

Injector

Engine speed

Engine

Intake manifold

Manifold pressuresensor

Air

Engine ECU


Fuel System Description

The fuel is taken from the fuel tank by the fuel pump and sprayed under pres-sure by an injector.The fuel pressure in the fuel line must be regulated to maintain stable fuel injec-tion by the pressure regulator and pulsa-tion damper.

Main components Fuel tank Fuel pump assembly

Fuel pump Fuel pump filter Fuel filter Pressure regulator

Delivery pipe Injector Pulsation damper

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Fuel Pump

The fuel pump is installed in the fuel tank and is integrated with the fuel filter, pres-sure regulator, fuel sender gauge, etc. The pump impeller is turned by the motor to compress the fuel. The check valve closes when the fuel pump is stopped to maintain the pres-sure in the fuel line and make it easier to restart the engine.If there is no residual pressure, vapor lock can easily occur at high tempera-tures, making restarting difficult. The relief valve opens when the pres-sure on the outlet side becomes too high in order to prevent the fuel pressure from becoming too high.

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Pulsationdamper

Pulsationdamper

Injector

Injector

Fuel tank

Fuel tank

Fuel pump

Fuel pumpFuel pump assembly

Fuel filter

Pressure regulator

Pressure regulator

Fuel pump filter

Fuel pump filter

Fuel filter

Delivery pipe

Delivery pipe

Inlet portOutlet port

Casing

Check valve

Relife valve

Pump impeller

Motor

Fuel pump filter

Fuel Impeller

Blade


Pressure Regulator

The pressure regulator controls the fuel pressure to the injector at 324 kPa (3.3 kgf/cm2). (Values may differ depending on engine models)In addition, the pressure regulator maintains the residual pressure in the fuel line in the same way as the fuel pump check valve.There are two types of fuel regulation methods.

1. Type 1This type controls the fuel pressure at a constant pres-sure.When the fuel pressure exceeds the force of the pres-sure regulator's spring, the valve opens to return fuel to the fuel tank and regulate the pressure.

HINT:The injection port of the injector is applied the vacuum by the manifold vacuum, which draws out the fuel. This vacuum is always changing depending on the engine conditions. Therefore, for this type the engine ECU calculates the fuel injection amount per injection duration in accordance with the changes in the intake manifold vacuum to ensure that the injector properly injects the fuel.

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2. Type 2This type is equipped with a delivery pipe that continu-ally regulates the fuel pressure to keep the fuel pres-sure higher than a determined pressure from the manifold pressure. The basic operation is the same as type 1, but because the manifold vacuum is applied to the dia-phragm's upper chamber, the fuel pressure is con-trolled by changing the fuel pressure when the valve is opened in accordance with the manifold vacuum. The fuel is returned to the fuel tank via the fuel return pipe.

HINT:The injection port of the injector is applied the vacuum by the manifold vacuum, which draws out the fuel. This vacuum is always changing depending on the engine conditions. Therefore, for this type the fuel pressure is continuously regulated in accordance with the intake manifold vacuum to keep the fuel pressure above a set pressure to maintain a set injection amount per injection duration.

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Valve

to Injector

Pressure regulator

Fuel filter

from Fuel pump

to Fuel tank

Diaphragm

fromDelivery pipe

toIntake manifold

Valve

to Fuel tank

Fuel tank

Pulsation damper

Pressure regulator Fuel return pipe


Pulsation Damper

The pulsation damper uses a diaphragm to absorb a slight amount of fuel pressure pulsation generated by the fuel injection and the compression of the fuel pump.

SERVICE HINT:

The fuel pressure can be inspected easily by the screw of the pulsation damper.

HINT:Some engine models do not have a pulsation damper.

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Injector

The injector injects fuel into the intake ports of the cylinders in accordance with the signal from the engine ECU. The signals from the engine ECU cause current to flow in the solenoid coil, which causes the plunger to be pulled, opening the valve to inject the fuel.Because the plunger stroke does not change, the amount of the fuel injection is controlled at the time the current is flowed to the solenoid.

SERVICE HINT:

Handling of the O-ring: The O-ring must not be reused. When installing the O-ring, first coat

it with new gasoline. When installing the injector to the

delivery pipe, be careful not to dam-age the O-ring.With the injector installed in the deliv-ery pipe, turn the indicator by hand. If it does not rotate smoothly, the O-ring is damaged.

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Plunger

Injector

Grommet

O-ring

Valve Coil


Fuel Filter/Fuel Pump Filter

1. Fuel filterThe fuel filter removes dirt and impu-rities from the fuel that is com-pressed by the fuel pump.

2. Fuel pump filterThe fuel pump filter removes dirt and impurities from the fuel before enter-ing the fuel pump.

SERVICE HINT:

If a fuel filter becomes clogged, it will reduce the fuel pressure sent to the injector, causing difficulties with engine starting or poor drivability.

HINT: Some fuel pumps are installed on

the outside of the fuel tank. In some models a union bolt or vari-

ous types of quick connectors are used to connect the fuel line.

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Fuel Pump Control

1. Basic operationThe fuel pump only operates when the engine is run-ning.Even when the ignition switch is turned ON, if the engine is not running, the fuel pump will not operate.

Fuel pump filter

Fuel filter

Engine ECU

CircuitopeningrelayEFI relay Fuel pump

IG

ST

NE signal

MicroprocessorFC

E1

STA

NE

Ignitionswitch


(1) Ignition switch ON: When the ignition switch is in the IG position, the EFI relay turns on.

(2) Ignition switch START: When the engine cranks, a STA signal (starter signal) is sent to the engine ECU from the ST terminal of the ignition switch.When the STA signal is input into the engine ECU, the engine turns on the transistor and the circuit opening relay is turned on. Then, current is allowed to flow into the fuel pump in order to operate the fuel pump.

Engine ECU


IG

ST

NE signal

MicroprocessorFC

E1

STA

NE

Ignitionswitch

Engine ECU


IG

ST

NE signal

MicroprocessorFC

E1

STA

NE

Ignitionswitch


(3) Engine cranking/running At the same time the engine is running, the engine ECU receives the NE signal from the crankshaft posi-tion sensor, continuing the transistor on to keep the fuel pump operating.

(4) If engine is stopped: Even when the ignition switch is ON, if the engine is stopped, the NE signal will no longer be input into the engine ECU, so the engine ECU will turn off the tran-sistor, which turns off the circuit opening relay, causing the fuel pump to stop.

Engine ECU


IG

ST

NE signal

MicroprocessorFC

E1

STA

NE

Ignitionswitch

Engine ECU


IG

ST

MicroprocessorFC

E1

STA

NE

Ignitionswitch

NE signal


SERVICE HINT:

DLC 1 There are some vehicles equipped with a DLC1 as shown at left.When +B terminal and FP terminal of the DLC1 are shorted using an SST with the ignition switch turned ON, the current will flow to the fuel pump without pass-ing through the circuit opening relay to operate the fuel pump.In this way, the inspection of the fuel pressure or pump operation can be performed by forcing the fuel pump to operate.

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2. Fuel pump speed controlThis control reduce the fuel pump speed to decrease the pump wear and electrical power when much fuel is not required, such as when the engine is running at low speed. When the current flows into the fuel pump through the contact B of the fuel pump control relay and the resis-tor, the fuel pump operates at low speed.When the engine is cranking, when the engine is run-ning at high speed, or at heavy loads, the engine ECU switches the contact of the fuel pump control relay into A in order to operate the fuel pump at high speed.

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Ignitionswitch

Engine ECU


SST

DLC1

IG

+BDLC1

FP

ST

NE signal

MicroprocessorFC

E1

STA

NE

Engine ECU

Circuitopeningrelay

Fuel pumpcontrol relay

Resistor

A

B

EFI relay Fuel pump

IG

ST

NE signal

MicroprocessorFP

FC

E1

STA

NE

Ignitionswitch


HINT:ON-OFF control with speed control (by engine ECU and fuel pump ECU)Some models control the fuel pump speed using the fuel pump ECU instead of the circuit opening relay, fuel pump control relay and resistor.In addition, this type of control also has a fuel pump system diagnostic function.When a malfunction is detected, a signal is sent from the fuel pump ECU to DI terminal of the engine ECU.

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3. Fuel pump shut-off systemSome vehicles have a mechanism where the fuel pump control stops the fuel pump in the following con-ditions to maintain safety.

(1) When an airbag inflates:When the SRS driver's, front passenger's, or side air-bag inflates, the fuel cut-off control stops the fuel pump.When the engine ECU detects an airbag inflation sig-nal from the center airbag sensor assembly, the engine ECU turns off the circuit opening relay to stop the fuel pump operation. After the fuel cut-off control operates, the fuel cut-off control can be cancelled by turning the ignition switch OFF, causing the fuel pump to reoperate.

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EngineECU

EFI relay Fuel pumpFuel pump ECU

FPC

FP+

FP-

D1

Engine ECU


Ignitionswitch

MicroprocessorFC

E1

STA

NE signal

Center airbag sensor assembly

NE

GSFC

GSW

IG

ST


(2) When the vehicle crashes or rolls over:When the vehicle crashes, the fuel pump inertia switch will turn off the fuel pump to minimize fuel leak-age.The fuel pump inertia switch is located between the fuel pump ECU and the engine ECU.When the ball in the switch moves at a collision, the switch is separated from the contact to turn it OFF and stop the fuel pump operation. After this fuel cut-off operates, push the reset switch to the top to reset the fuel cut-off control, causing the fuel pump to reoperate.

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Injection Duration Control Fuel Injection Methods and Injection Timing

The fuel injection methods are to inject the fuel indepen-dently in each cylinder or to simultaneously inject the fuel into all the cylinders. There are also various injection tim-ings, such as injecting at a determined timing or injecting in accordance with the changes in the amount of the intake air or engine speed. The basic fuel injection method and injection timing are as follows. In addition, the larger the injection volume is, the start of the injection timing becomes faster.

M

EngineECU

Link

Acceleration

Link

Ball

Ball

System diagram

Detecting a collisionNormal

Movement

Contactpoint(ON)

Contactpoint

Resetswitch

EFI mainrelay

FP+Fuelpump

Fuel pumpinertia switch

FP-

FPCDI

+BFuelpumpECU



Contactpoint(OFF)

Indipendent (Sequential)

Groups

Simultaneous

360

Crankshaft angle


1. Independent (Sequential) Fuel is injected independently for each cylinder once for every two crankshaft rotations.

2. Groups The fuel is injected for each group once for every two crankshaft rotations. 2 groups 3 groups 4 groups

Intake stroke

Independent (Sequential)

Ignition

Fuel injection

0 360

Crankshaft angle

1080

1

3

4

2

1

Groups

2 groups

3 groups

Intake stroke Fuel injection

53624

153624

4 groups

Crankshaft angle

18436

75

2

Ignition

0 360 1080


3. Simultaneous The fuel is simultaneously injected to the respective cylinders once for each rotation of the crankshaft.The amount of fuel required for combustion is injected over two injections.

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Fuel Injection Duration Control

The engine ECU changes the fuel injection volume by changing the injector injection duration.The actual fuel injection duration is determined by the fol-lowing two items.

1. The basic injection duration is determined by the amount of the intake air and the engine speed.

2. The various corrective injection durations are deter-mined by the signals from the various sensors.

The injection duration that the engine ECU finally outputs into the injector is added various corrections to the basic injection duration. There are following corrections:

Start enrichment Warm-up enrichment Air-fuel ratio feedback correction (some models only) Acceleration enrichment Fuel cut-off Power enrichment Other corrections

Intake stroke

Simultaneous

Fuel injection

Crankshaft angle

1

3

4

2

Ignition

0 360 1080

Intake air temp. correctionPower enrichment

Startenrichment

Warm-upenrichment

Air-fuel ratiofeedbackcorrection

Injection Duration =Basic injection duration + Corrective injection duration

Fuel cut-offAccelerationenrichment


Various corrections and signals

Various Corrections

1. Start enrichmentThe basic injection duration cannot be calculated from the amount of the intake air because the engine speed is low and the changes in the amount of the intake air are large at starting. For this reason, the fuel injection duration at starting is determined from the coolant temperature. The coolant temperature is detected by the water tem-perature sensor.The lower the water temperature is the fuel vaporiza-tion becomes worse. Therefore, the air-fuel mixture is made richer by lengthening the injection duration. The engine ECU determines that the engine is being started when the engine speed is 400 rpm or less. In addition, when the engine speed suddenly falls below 400 rpm due to a sudden increase of the load on the engine, a hysteresis is used to prevent the engine ECU from determining that an engine that has already been started is being started again unless the engine speed falls below 200 rpm.

SERVICE HINT:

When there is a malfunction with the water temperature sensor, it can be considered as the worse startability.

REFERENCE:To improve startability while the engine was cold, the old type of EFI had a cold start injector and cold start time switch in addition to the regular injector to increase the fuel volume at starting.

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Sensor Signal

VG / PIM

NE

G

THW

IDL

VTA

OX1A, OX1B

Basicinjectionduration Startenrichment

Various corrections

Air flow meter/Manifold pressuresensor

Crankshaftposition sensor

Camshaftposition sensor

Water temp.sensor

Throttleposition sensor

Oxygen sensor

Warm-upenrichment

Air-fuelratio feedbackcorrection

Accelerationenrichment

Fuelcut-off

Powerenrichment

Low

400rpm Normalcondition

Startingstate

Hysteresis

Long

STARTON

Short

Injectionduration

Coolant temp. High0


2. Warm-up enrichmentThe amount of the fuel injection is increased because the fuel vaporization is poor during the cold engine. When the coolant temperature is low, the fuel injection duration is increased to make the air-fuel mixture richer in order to attain the drivability during the cold engine. The maximum correction is twice as long as normal temperature.

SERVICE HINT:

When there is a malfunction with the water temperature sensor, it can be considered as poor drivability.

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3. Air-fuel ratio feedback correction (For most mod-els)When there are no major fluctuations in the engine load or engine speed, such as when idling or driving at constant speed after warming up, fuel (air-fuel mixture close to the theoretical air-fuel ratio) is supplied based on the amount of the intake air. The following corrections are activated when driving at a constant speed after warming up.

(1) Feedback control using the oxygen sensor (Air-fuel ratio feedback control):The engine ECU determines the basic injection dura-tion to achieve the theoretical air-fuel ratio. However, a slight deviation from the theoretical air-fuel ratio occurs in accordance with the actual engine con-ditions, changes over time, and other conditions. Therefore, an oxygen sensor detects the oxygen con-centration in the exhaust gas to determine if the cur-rent fuel injection duration becomes the theoretical air-fuel ratio against the amount of the intake air. If the engine ECU determines from signals of the oxy-gen sensor that the air-fuel ratio is richer than the the-oretical air-fuel ratio, it shortens the injection duration to make the air-fuel mixture leaner. Conversely, if it determines that the air-fuel ratio is lean, it will lengthen the injection duration to make the air-fuel mixture richer.The feedback control operates to maintain the aver-age air-fuel ratio at the theoretical air-fuel ratio by repeatedly performing minor corrections. (This is called a "closed-loop" operation.)

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Large

Small

Low High

Amountof injectiondurationcorrection

0

Coolant temp.

Rich

0.45 V

Lean

Rich

Lean

Oxygen sensor

ECU Determinationof Engine ECU

Feedbackcorrection

Decrease Increase

Decrease Increase


In order to prevent overheating of the catalyst and assure good engine operation, air -furl ratio feedback does not occur under the following conditions (open-loop opera-tion):

During engine starting During after-start enrichment During power enrichment When the coolant temperature is below a determined

level When fuel cut-off occurs When the lean signal continues longer than a deter-

mined time The center point (a) changes during the feedback control such as time passes. In this case, the center point is forced to be returned to the center. If it is not, it will cause the out of the correction range of the feedback control. This is called air-fuel ratio learned control or long fuel trim.

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(2) Feedback control using the air-fuel ratio sensor (A/F sensor):The output voltage of the oxygen sensor changes rap-idly around the theoretical air-fuel ratio as shown in the illustration (upper). The A/F sensor data which the engine ECU attains is displayed in the hand-held tester. (When the air-fuel ration is lean, the voltage is high. Conversely, the volt-age is low when rich.)As a result, the detection precision of the air-fuel ratio has been improved. If the current air-fuel ratio changes from the theoretical air-fuel ratio as shown in the illustration (below), the engine ECU continuously corrects the air-fuel ratio using the oxygen sensor signal. For the A/F sensor, however, the engine ECU corrects instantly by determining the amount of change from the theoretical air-fuel ratio.

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1.2

1.01.0

0.8

1.2

a aa

0.8

Correctionratio

Correctionrange

Rich mixture

Air-fuel ratio learned control

Lean mixture

Normal condition Over life time

Central feedback value

Theoreticalair-fuel ratio

Rich

Lean

Output characteristics

(V)4.2

2.211 14.7 19

(V)1

0.1

Disorder

Injectionvolume

A/F sensor

A/F sensor

Air-fuel ratio sensor

Air-fuelratiosensor

Air-fuel ratia

Oxygensensor

Oxygen sensor

Oxy

gen

sens

or o

utpu

t

Dat

a of

A/F

sen

sor

Oxygensensor

Correction at aconstant proportion

Immediate correction

EngineECU

AF+3.3V

3.0VAF-


(3) CO emission control correction for vehicles without an oxygen sensor or A/F sensor:For vehicles without an oxygen sensor or A/F sensor, a variable resistor can be used to adjust the CO con-centration (%) during idling.Turning the resistor to the R side makes the concen-tration richer, and turning it to the L side makes it leaner. For vehicles equipped with an oxygen sensor or A/F sensor, however, CO adjustment is not required dur-ing idling because these vehicles are automatically adjusted to the proper air-fuel ratio using the sensor signal.

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4. Acceleration enrichmentThe air-fuel ratio becomes lean, especially during the start of acceleration because a fuel supply lag tends to occur during acceleration against the rapid change of the amount of the intake air when the accelerator pedal is depressed.For this reason, the injection duration is lengthened to increase the fuel injection volume against the intake air to prevent the air-fuel mixture from becoming lean. The acceleration is determined by the speed of the change in the throttle valve opening angle. The correction during acceleration increases greatly during the start of acceleration and is gradually reduced thereafter until the increase has ended.In addition, the more rapid the acceleration is, the larger the fuel injection volume increase.

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L R

LR

180

SST

Rich mixture

Leaner

Injection volumeVariableresistor

Increased

Decreased

Engine ECU

Injector

Lean mixture

RicherIdle mixtureadjustingscrew

Large

LargeChange of the amountof the intake air

Small

Small

Correctionvolume

Large

Small

Correctionvolume

Time

Slow acceleration

Sudden acceleration


5. Fuel cut-offDuring deceleration, injection operation is stopped according to the deceleration condition in order to reduce the harmful exhaust gases and improve the engine braking effect. Then the fuel cut-off control is activated to cut-off the fuel injection. The state of deceleration is determined from the throt-tle valve opening and the engine speed. When the throttle valve is closed and the engine speed is high, it is determined that the vehicle is decelerating.

Fuel cut-off controlThe fuel cut-off control stops the fuel injection when the engine speed is higher than a determined speed and the throttle valve is closed. Fuel injection will resume when the engine speed slows to a determined speed or the throttle valve is opened. The fuel cut-off engine speed and fuel injection resump-tion engine speed will increase when the coolant temper-ature is low.In addition, the fuel cut-off engine speed and fuel injection resumption engine speed are increased when the air con-ditioner switch is on to prevent the engine speed from fall-ing and an engine from stalling.There are also some engine models in which these engine speeds drop during braking (i.e., when the stop light switch is on).

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6. Power enrichmentAs there is a large amount of the intake air at heavy loads, such as when climbing a steep hill, it is difficult to sufficiently mix the injected fuel with the intake air. And all of the intake air is not used during combustion, causing some to remain.Therefore, more fuel than for the theoretical air-fuel ratio is injected to use all of the intake air in combus-tion to increase power. Heavy loads are determined from the throttle position sensor opening, engine speed, and intake air mass (VG or PIM). The greater the intake air mass (VG or PIM) or the higher the engine speed is, the ratio of the increased amount becomes larger.In addition, the amount is further increased when the throttle valve opening angle becomes a certain value or more.The correction of the increased amount is from approx. 10% to 30%.

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Coolant temperature

Injection resumption

Fuel cut-off

Eng

ine

spee

d

Low High


7. Intake air temperature correctionThe air density changes depending on the air tempera-ture.For this reason, a correction must be made to increase or decrease the fuel volume in accordance with the intake air temperature to optimize the mixture ratio required for the current engine conditions. The intake air temperature is detected by the intake air temperature sensor. The engine ECU is set to a standard intake air tempera-ture of 20 C (68 F).The correction amount is determined when the tempera-ture rises above or falls below this temperature. When the intake air temperature is low, the amount is increased because the air density is high. When at high temperature, the amount is decreased because the air density is low. The correction of the increased/decreased amount is approx. 10%.

HINT:For hot-wire type air flow meters, the air flow meter itself outputs a corrective signal for the intake air tem-perature. Therefore, intake air temperature correction is not required.

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8. Voltage correctionThere is a slight delay between the time where the engine ECU sends an injection signal to the injector, and the time when the injector actually injects the fuel.If there is a severe drop in battery voltage, then this delay will be longer. This means that the time the injector injects the fuel is shorter than the time calculated by the engine ECU. Therefore, the ratio of air becomes higher (in other words, leaner) than the mixture ratio required by the engine.For this reason, the engine ECU adjusts this by mak-ing the injector injection duration longer in accordance with the battery voltage drop.

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Intake air temperature

Cor

rect

ion

coef

ficie

nt

Low

1.0

20(68)

High

Battery voltage (V)

Standard operating delay time

Cor

rect

ive

inje

ctio

ndu

ratio

n (m

sec)

Low

On

Off

Open

Close

Injector actually open

Injection signalVoltage correction

14High


Exercise

These are the pre-course study materials for the Frequent Service Job Course. The objective of this course is to learn the work procedure and points of frequent service jobs. In the pre-course study, you will study the basic knowledge needed for repair work, and the basic mechanism and operation of automobiles. After you finish studying all of the chapters, please take the Examination.

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Diagnosis Master Technician - Gasoline Engine Control System EFI (Electronic Fuel Injection)Question- 1- 20 -

The following statements pertain to the EFI. Mark each of the following statements True or False.

Question- 2

The following illustration shows the fuel pump control circuit. For its operation, select the statement that is False.

No. Question True or False Correct Answers

1 The engine ECU always determines the proper fuel injection volume based on the signals from various sensors. True False

2 The check valve of the fuel pump closes to maintain the remaining pressure in the fuel line when the fuel pump is stopped. True False

3 The pressure regulator of recent models constantly controls the fuel pressure at higher pressure against the intake manifold pressure. True False

4 The pulsation damper absorbs the fuel pressure pulsation in the fuel line. True False

1. The engine ECU turns on the circuit opening relay and the fuel pump operates while the ignition switch is at IG position.

2. The STA signal is input in the engine ECU and the fuel pump operates while the ignition switch is at ST position.

3. The NE signal is input in the engine ECU while the engine is running and the fuel pump operates contin-uously.

4. If the engine is stalled, the fuel pump is stopped because the NE signal is not input in the engine ECU even if the ignition switch is at IG position.

Engine ECU

Circuit openingrelayEFI relay Fuel pump

IG

ST

NE signal

MicroprocessorFCE1

STA

NE

Ignitionswitch

Diagnosis Master Technician - Gasoline Engine Control System EFI (Electronic Fuel Injection)Question- 3- 21 -

The following statements pertain to the basic injection duration. Mark each of the following statements True or False.

Question- 4

About the condition that the air-fuel ratio feedback correction stops, mark each of the following statements True or False.

Question- 5

The following statements pertain to the acceleration enrichment. Select the statement that is True.


1 The basic injection duration is determined by the accelerator open-ing angle and the engine speed. True False

2 The corrective injection duration is calculated from the engine condi-tion detected by various sensors. True False

3 Actual injection duration = Basic injection duration + Corrective injection duration True False

4 The injection duration becomes longer by the warm-up enrichment because the fuel is difficult to be vaporized during a cold engine. True False


1 During engine starting. True False

2 After engine warm-up (Coolant temperature: more than 50C (122 C)) True False

3 During correction of acceleration enrichment and power enrichment. True False

4 During the fuel cut-off control. True False

5 When the output from the oxygen sensor is 0 V (lean) more than 15 seconds. True False

1. The acceleration is detected by the vehicle speed sensor.

2. For the acceleration enrichment, the fuel increases greatly during the start of the acceleration and is gradually reduced thereafter until the increase has ended.

3. The more rapid acceleration is, the smaller the injection volume increases.

4. The acceleration is detected by the crankshaft position sensor and camshaft position sensor.

21.13_EFI ok

Documents

fuel pressure

fuel line

fuel sender gauge

optimum fuel injection

stable fuel injection

intake air mass

intake air density

air volume