Deck 30: Electronic Fuel Injection

Question 1

The strength of the mass airflow (MAF)signal is determined by the energy needed to keep the heated sensing element at a constant temperature above the incoming ambient air temperature.

Answer 1

True

Question 2

Today the most commonly used EFI system is the mass airflow (MAF)system which relies on a MAF sensor that directly measures the amount of intake air.

Answer 2

True

Question 3

Idle speed control is a function of the PCM.

Answer 3

True

Question 4

GDI [gasoline direct injection] systems allow engines to run at very lean air/fuel ratios and eliminate the need for EGR systems.

Question 5

Bottom-feed injectors used in throttle body injection (TBI)systems are able to use fuel pressures as low as 10 psi.

Question 6

PFI systems use at least one injector at each cylinder.

Question 7

The PCM may order a richer fuel mixture when the engine is overheating.

Question 8

Because modern engines heat up rapidly, heated oxygen sensors (HO₂S)are not needed.

Question 9

The throttle stop screw on modern throttle bodies is used to adjust the idle speed.

Question 10

CPI (central multiport injection)injectors are located in the lower half of the intake manifold.

Question 11

Fuel injectors are electromechanical devices.

Question 12

The mass airflow (MAF)sensor measures changes in the intake manifold pressure that result from changes in engine load and speed.

Question 13

The auxiliary air valve is controlled by the PCM.

Question 14

To prevent fuel boiling in the TBI assembly, the fuel pressure is kept high.

Question 15

During closed loop engine mode, injector pulse width is controlled according to predetermined parameters held in the PCM's memory.

Question 16

All throttle body assemblies should be cleaned whenever the air filter is changed.

Question 17

OBD-II systems have only one O₂S (oxygen sensor)in the exhaust system, located after the catalytic converter (downstream).

Question 18

Nearly all of today's diesel systems have a common rail injection system in which the injectors are directly controlled by the PCM.

Question 19

To meet OBD II regulations, an updated version of the central port injection (CPI)system uses individual injectors for each poppet nozzle. This system, called central sequential fuel injection (CSFI)allows each injector to be shut off in the event of a misfire.

Question 20

Fuel trim can be monitored for diagnostic purposes.

Question 21

The throttle body of a port fuel injected engine may include any of the following components EXCEPT:

A)idle air control motor
B)single or double bores with throttle plates
C)throttle position sensor
D)oxygen sensor

Question 22

While discussing PFI systems, Technician A says the PCM provides the proper air/fuel ratio by controlling the fuel pressure. Technician B says the PCM provides the proper air/fuel ratio by controlling the injector pulse width. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 23

An O-ring at the base of a fuel injector ______.

A)seals the injector to its mounting position
B)provides thermal insulation to prevent the formation of vapor bubbles
C)dampens potentially damaging vibrations
D)All the answers are correct.

Question 24

Fuel injector firing is being discussed. Technician A says SFI systems control each injector separately so that it fires just before the intake valve opens. Technician B says sequential injector firing is more accurate than multiport systems. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 25

Typical fuel injector pulse widths range from _____ to _____ milliseconds.

A)1; 10
B)10; 100
C)100; 1,000
D)1,000; 10,000

Question 26

Technician A says pulsation dampers reduce the pressure pulsations caused by the rapid opening and closing of the fuel injectors. Technician B says the damper helps to reduce fuel noise and maintains pressure during engine cooldown. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 27

MAP output is the same as what is measured on a vacuum gauge. When intake vacuum is high, MAP voltage is high.

Question 28

Technician A says the vacuum hose on the fuel pressure regulator of a PFI system is connected to the intake manifold. Technician B says the fuel pressure regulator of a TBI injection system doesn't need a vacuum hose to regulate pressure because the injectors are located above the throttle plate where the air pressure is constant. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 29

Technician A says piezoelectric injectors rely on stacked crystals that expand when a voltage is applied. Technician B says piezoelectric injectors are slower acting than solenoid-type injectors. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 30

Fuel injectors may be controlled ______.

A)in pairs or groups
B)all at once
C)sequentially
D)All the answers are correct.

Question 31

Technician A says an air/fuel ratio sensor responds to minor changes in the air/fuel mixture. Technician B says that when an air/fuel ratio sensor is used on an OBD-II vehicle, both the upstream and downstream sensors must be air/fuel ratio type sensors. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 32

Which of the following is NOT representative of sequential fuel injection systems?

A)They have one injector per cylinder
B)Injectors are located in the intake manifold ports
C)All injectors receive the same PCM commands simultaneously
D)None of the answers is correct.

Question 33

Technician A says in a returnless fuel system, the pressure regulator is mounted on the fuel rail. Technician B says in a returnless fuel system the pressure regulator, fuel sender, and pump assembly are combined in one unit inside the fuel tank. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 34

While discussing central port injection (CPI), Technician A says the poppet nozzles are opened by the computer. Technician B says the poppet nozzles are opened by fuel pressure. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 35

Technician A says a throttle body may house one fuel injector. Technician B says a throttle body may house two fuel injectors. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 36

Technician A says throttle-by-wire systems (ETC)eliminate the need for a cruise control actuator. Technician B says ETC also allows the PCM to be more effective when limiting engine and vehicle speeds. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 37

Technician A says TBI systems use top fuel-feeding injectors. Technician B says PFI systems use bottom fuel-feeding injectors. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 38

Technician A says the computer uses the TP sensor and ECT sensor signals to determine the amount of air entering the engine in a speed-density system. Technician B says the computer uses the TP sensor and oxygen sensor signals to determine the amount of air entering the engine in a speed-density system. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 39

In closed loop, the PCM adjusts the pulse width according to inputs from a variety of sensors, but primarily the _____.

A)TP (throttle position)
B)ECT (engine coolant temperature)
C)IAT (intake air temperature)
D)O₂S (oxygen sensor)

Question 40

While cranking a fuel injected engine and holding the accelerator to the wide-open throttle position, the air/fuel mixture will be ______.

A)lean
B)normal
C)rich
D)stoichiometric

Question 41

A sudden increase in TP voltage tells the PCM to _____ to prevent hesitation and stumbling during acceleration.

A)advance base ignition timing
B)retract the IAC valve pintle
C)momentarily enrich the mixture
D)open the EGR valve

Question 42

Which of the following is NOT a component of a throttle-by-wire system?

A)accelerator pedal position sensor
B)throttle position sensor
C)throttle control motor
D)IAC motor (idle air control)

Question 43

A CPI (central multiport injection)fuel injection system for a six-cylinder engine has ______.

A)only one injector solenoid
B)six poppet nozzles
C)a single fuel pressure regulator
D)All the answers are correct.

Question 44

The fuel pressure regulator can be located _____.

A)on the throttle body
B)on the fuel rail
C)inside the fuel tank
D)All the answers are correct.

Question 45

Each fuel injector has a _____-wire connector.

A)one
B)two
C)three
D)four

Question 46

Technician A says when the ECT sensor detects low engine temperature, the PCM decreases the injection pulse width. Technician B says when the TP sensor detects a sudden increase in throttle angle, the PCM increases the injectors' pulse width. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 47

Technician A says the fuel pressure regulator in a PFI system senses manifold vacuum and  continually adjusts the fuel pressure to maintain a constant pressure drop across the injector. Technician B says the pressure regulator in a PFI system is designed to provide a constant pressure to the fuel injector throughout the range of engine loads and speeds. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 48

Fuel trim is being discussed. Technician A says a positive fuel-trim value means the PCM detects a lean mixture and is increasing the pulse width to add more fuel to the mixture. Technician B says LTFT [long-term fuel trim] is erased when the ignition is turned off. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 49

The most important sensor in the fuel management system is _____.

A)MAF (mass airflow)
B)MAP (manifold absolute pressure)
C)oxygen sensor
D)CKP (crankshaft position sensor)

Question 50

A fuel injection system that uses a MAP sensor [manifold absolute pressure] to determine the amount of air entering the engine is called a _____-type injection system.

A)common rail
B)mass airflow
C)stoichiometric
D)speed density

Question 51

The longest injector pulse width occurs during ______.

A)deceleration
B)idle
C)acceleration
D)cold starting

Question 52

Technician A says the air/fuel ratio of a GDI (gasoline direct injection)engine can be as high as 60 to 1. Technician B says because the air/fuel ratios are so lean, GDI engines require lower compression ratios to prevent detonation. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 53

Technician A says an SFI is more efficient than an MFI injection because fuel is injected only when the intake valve is open, so the fuel can't condense when the intake valve is closed. Technician B says an MFI injection system can shut down the injector for a misfiring cylinder, preventing catalytic converter overheating. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 54

Only _____ meets the requirements of OBD II regulations.

A)MPI (multipoint injection)
B)TBI (throttle body injection)
C)TPI (tuned port injection)
D)SFI (sequential fuel injection)

Question 55

Technician A says the oxygen sensor (O₂S)detects misfires by monitoring the amount of unburned fuel in the exhaust system. Technician B says a heating element inside the sensor allows the sensor to reach operating temperature quickly and to maintain its temperature during periods of idling or low engine load. Who is correct?

A)A only
B)B only
C)both A and B
D)neither A nor B

Question 56

Which sensor synchronizes the firing of the injectors and determines when piston number 1 is on the compression stroke?

A)CKP (crankshaft position sensor)
B)CMP (camshaft position sensor)
C)TPS (throttle position sensor)
D)VSS (vehicle speed sensor)

Question 57

IAC (idle air control)valves are operated by a ______.

A)vacuum servo
B)reversible DC electric motor
C)stepper motor
D)All the answers are correct.

Question 58

If the throttle is held wide open while the engine is cranked over by the starter motor, the fuel management system will enter _____ mode.

A)closed loop
B)open loop
C)clear flood
D)maximum fuel delivery

Question 59

Which of the following is NOT an operating mode of a GDI (gasoline direct injection)engine?

A)idle mode
B)full-power mode
C)stoichiometric mode
D)lean burn (stratified)mode

Question 60

In most TBI systems, the fuel pressure is maintained at _____.

A)2 to 7 psi (14 to 49 kPa)
B)10 to 25 psi (70 to 172 kPa)
C)30 to 45 psi (210 to 315 kPa)
D)60 to 125 psi (420 to 875 kPa)

Question 61

The ____________________ in a TBI system is designed to provide a constant pressure on the fuel injector throughout the range of engine loads and speeds.

Question 62

The IAC system uses a ____________________ motor to retract or extend the IAC valve.

Question 63

The high-pressure fuel pump used in GDI ( gasoline direct injection)is driven by the ____________________.

Question 64

The ____________________ in a PFI system controls the amount of air that enters the engine as well as the amount of vacuum in the intake manifold.

Question 65

In TBI, MFI, and SFI systems, the fuel pressure must be high enough to prevent fuel ____________________.

Question 66

Explain the major differences between throttle body injectors and port fuel injectors.

Question 67

The ____________________ system controls idle speed by opening and closing a bypass passage in the throttle body in response to commands from the PCM.

Question 68

The ____________________ receives signals from all the system sensors, processes them, and transmits programmed electrical pulses to the fuel injectors.

Question 69

The ideal, or stoichiometric mixture of air and fuel for a gasoline engine is ____________________ to 1.

Question 70

A speed-density EFI system computer determines the amount of air entering the engine from the ____________________ sensor and engine rpm input signals.

Question 71

The length of time an injector is energized is called the ____________________ width.

Question 72

A mass airflow-type fuel injection system uses a ____________________ sensor to determine the amount of air entering the engine.

Question 73

In ____________________ systems, the injectors are grouped together in pairs or groups, and these pairs or groups of injectors are turned on at the same time.

Question 74

In a GDI system, the fuel is injected at pressures above ____________________ psi.

Question 75

The ____________________ helps to maintain constant fuel pressure, reduces fuel noise, and maintains pressure during engine cool down.

Question 76

____________________ systems inject gasoline directly into the cylinders.

Question 77

In a GDI (gasoline direct injection)system, the tip of the injector is located ______.

A)inside the combustion chamber
B)on the throttle body
C)in the intake port
D)in the intake manifold plenum

Question 78

Fuel injectors are ____________________ top and bottom devices.

Question 79

____________________ systems inject fuel above the throttle plates.

Question 80

The injectors on a modern port fuel injection system receive fuel from the ____________________.