Deck 16: Variable Geometry and Series Turbochargers

Question 1

What is the primary purpose of a variable-geometry turbocharger (VGT)?

A)To decrease cylinder pressures.
B)To increase oxygen content.
C)To reduce intake air oxygen content.
D)To create exhaust backpressure.

Answer 1

D

Question 2

What characteristic of VGTs requires the use of titanium alloys for compressor wheels?

A)Low-pressure ratios.
B)Higher compressor discharge temperatures.
C)Increased turbine speed.
D)EGR gas flow across the compressor wheel.

Answer 2

B

Question 3

Consider a VGT. When intake boost pressure is at its highest value, what can most likely be observed regarding exhaust backpressure in the exhaust manifold?

A)It is also at its highest value.
B)It is at a low value.
C)It depends on the EGR gas requirements.
D)It is low because the waste gate will usually open.

Answer 3

A

Question 4

Technician A says that a late-model engine equipped with a VGT will close the vanes to increase intake boost and exhaust backpressure during braking. Technician B says the vanes will open to reduce intake airflow during engine braking. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 5

Which of the following conditions is required to increase the turbine speed of a VGT?

A)Widening the turbine nozzle ring opening or exit area.
B)Narrowing the turbine nozzle ring opening or exit area.
C)Increasing EGR flow.
D)Decreasing EGR flow.

Question 6

Which of the following strategies best explains how the VGT operates as an engine brake?

A)It narrows the nozzle ring to increase exhaust backpressure and boost pressure.
B)It narrows the nozzle ring to decrease exhaust backpressure and increase boost pressure.
C)It widens the nozzle ring to increase exhaust backpressure and boost pressure.
D)It widens the nozzle ring to decrease exhaust backpressure and boost pressure.

Question 7

Which VGT sensor is primarily responsible for preventing turbocharger overspeed?

A)Exhaust backpressure.
B)Mass airflow.
C)Boost pressure.
D)A variable reluctance sensor located on the turbine shaft.

Question 8

A typical VGT produced since 2010 will most commonly respond to electrical signals transmitted ____________.

A)directly from the ECM
B)from an engine controller
C)through the onboard vehicle network
D)from the EGR control module

Question 9

Which of the following conditions is required to decrease the turbine speed of a VGT?

A)Opening or widening the turbine nozzle ring exit area.
B)Narrowing the turbine nozzle ring exit area.
C)Increasing EGR flow.
D)Decreasing EGR flow.

Question 10

Technician A says that VGT engines can electronically vary turbocharger boost pressure. Technician B says that boost pressure from VGTs is typically higher than boost pressure from fixed-geometry turbochargers. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 11

Technician A says that without power to the VGT actuators, some actuators will typically provide a lot of boost, because the vanes are as much as 95% closed. Technician B says the turbocharger will not provide very much boost, because the vanes always default to an open position. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 12

Technician A says the turbocharger speed sensor is used to sense and prevent a turbocharger overspeed condition. Technician B says the speed sensor is used by the OBD system to detect faults with the turbocharger. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 13

After two technicians had listened to the noise made by a VGT when the key was switched on but before starting the engine, Technician A said the noise was the actuator moving to a default spring-loaded position after it had been shut down in a wide-open position. Technician B said the turbocharger actuator was relearning maximum and minimum actuator sweep positions during a self calibration process. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 14

Technician A says that VGT engines have less turbo lag. Technician B says VGT engines have more exhaust backpressure in the exhaust manifold than single-stage turbochargers have. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 15

Technician A says that coolant passageways through the turbocharger housing are used to keep the turbocharger bearings and other parts cooled when the engine is running. Technician B says that coolant passageways are used primarily to circulate coolant after the engine has been shut off. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 16

Technician A says the operation of the VGT actuator's electric motor is inspected during a bounce test. Technician B says the motor needs to be removed and checked by using an ohmmeter to determine whether it is faulty. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 17

While two technicians are discussing series turbocharging, Technician A says the high-pressure turbocharger has an exhaust bypass valve that prevents overspeeding. Technician B says the low-pressure turbocharger uses a waste gate to direct exhaust gases to the high-pressure turbocharger. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 18

Under which of the following operating conditions does the low-pressure turbocharger of a series turbocharger arrangement produce maximum boost?

A)High-speed, high-load operation.
B)Low-speed low-load operation.
C)High-speed, low-load operation.
D)Any low-load operation.

Question 19

Consider the operation of a single-sequential DualBoost turbocharger. What combination of air inlets and outlets are used?

A)One air inlet and two outlets.
B)Two air inlets and one outlet.
C)Two inlets and two outlets.
D)A dual path air inlet and bypass valve-regulated outlet.

Question 20

Technician A says that single-sequential turbochargers have two separate compressor and turbine housings. Technician B says that single-sequential turbochargers use two turbine wheels and one compressor wheel. Who is correct?

A)Technician A
B)Technician B
C)Both A and B
D)Neither A nor B

Question 21

What characteristic of VGTs requires the use of titanium alloys for compressor wheels?

A)Low-pressure ratios."
B)Higher compressor discharge temperatures."
C)Increased turbine speed.
D)EGR gas flow across the compressor wheel."

Question 22

Technician A says that a late-model engine equipped with a VGT will close the vanes to increase intake boost and exhaust backpressure during braking. Technician B says the vanes will open to reduce intake airflow during engine braking. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 23

A VGT (variable-geometry turbocharger) has the functional capability of changing intake boost pressure and exhaust backpressure independent of:

A)engine speed"
B)intake pressure"
C)exhaust pressure
D)intake temperature"

Question 24

Since the VGT (variable-geometry turbocharger) pressure ratios are higher, more discharge heat is generated by the compressor wheel, which often requires:

A)titanium alloys"
B)aluminum alloys"
C)steel alloys
D)forged aluminum alloy"

Question 25

Approximately _____ percentage of the intake charge in diesels can be exhaust gas.

A)70%"
B)60%"
C)50%
D)40%"

Question 26

What exhaust backpressure is required in some engines to force enough exhaust gas into the fresh-air intake turbochargers?

A)30 psi"
B)40 psi"
C)60 psi
D)80 psi"

Question 27

Technician A says that exhaust backpressure is built up in the exhaust manifold before entering the turbocharger. Technician B says that an EGR flow control valve diverts intake air into the intake manifold. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 28

What is experienced as a delay between the driver's demand for power from the engine and the point in time when the engine responds with power in proportion to the driver's demand?

A)Ignition delay"
B)Throttle delay"
C)Combustion lag
D)Combustion lag"

Question 29

Technician A says that air reaches a cylinder more slowly in comparison to fuel, which can change dramatically from one combustion event to the next. Technician B says that smaller turbocharger compressor housings and wheels can produce proportionally greater airflow for better performance and reduced emissions. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 30

Which of the following allow more turbocharger exhaust flow in high horsepower engines?

A)Larger exhaust pipes"
B)Larger turbine housings"
C)Smaller turbine housings
D)Smaller A/R ratios"

Question 31

Increased inertia from heavier turbine and compressor wheel mass, along with bigger housings, means the turbocharger will take longer to spool, or build boost pressure, which in turn increases:

A)ignition delay"
B)throttle delay"
C)combustion lag
D)turbo lag"

Question 32

Higher turbine speeds are possible when using:

A)smaller lightweight turbine wheels"
B)larger lightweight turbine wheels"
C)waste-gate controls
D)turbo boost valve"

Question 33

What can enable higher turbine speeds?

A)Widening the width of the nozzle ring opening area"
B)Narrowing the width of the waste-gate opening area"
C)Narrowing the width of the boost valve ring opening area
D)Narrowing the width of the nozzle ring opening area"

Question 34

Technician A says that driving the turbine wheel at higher speeds enables very high compressor wheel speeds. Technician B says that pairing low inertia rotating components with electronic turbocharger controls provides adequate air and exhaust gas flow over an extended operational range. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 35

The VGT (variable-geometry turbocharger) electronic actuator communicates with other:

A)ECMs (engine control modules)"
B)TCMs (transmission control Modules)"
C)EBCMs (electronic brake control modules)
D)Vehicle control modules"

Question 36

Technician A says that creating higher backpressure speeds up the turbocharger, which decreases boost pressure. Technician B says that vanes surrounding the turbine wheel can move from open to a closed position to regulate the flow of exhaust gases across the turbine. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 37

Which of the following strategies best explains how the VGT operates as an engine brake?

A)It narrows the nozzle ring to increase exhaust backpressure and boost pressure."
B)It narrows the nozzle ring to decrease exhaust backpressure and increase boost pressure."
C)It widens the nozzle ring to increase exhaust backpressure and boost pressure.
D)It widens the nozzle ring to decrease exhaust backpressure and boost pressure."

Question 38

A typical VGT produced since 2010 will most commonly respond to electrical signals transmitted ____________.

A)directly from the ECM"
B)from an engine controller"
C)through the onboard vehicle network
D)from the EGR control module"

Question 39

Technician A says that VGT engines can electronically vary turbocharger boost pressure. Technician B says that boost pressure from VGTs is typically higher than boost pressure from fixed-geometry turbochargers. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 40

After two technicians had listened to the noise made by a VGT when the key was switched on but before starting the engine, Technician A said the noise was the actuator moving to a default spring-loaded position after it had been shut down in a wide-open position. Technician B said the turbocharger actuator was relearning maximum and minimum actuator sweep positions during a self calibration process. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 41

VGTs (variable-geometry turbochargers) are built along ____ designs.

A)1"
B)2"
C)3
D)4"

Question 42

Two technicians are discussing VGT's (variable-geometry turbochargers') variable-nozzle opening. Technician A says when less exhaust gas flow takes place across the turbine, the turbine speed drops because exhaust backpressure increases. Technician B says that by varying the width of the nozzle opening with an actuator, the turbine speed power is adjusted to provide just enough energy to drive the compressor wheel at the desired boost level for any engine speed and load condition. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 43

The position of the VGT (variable-geometry turbochargers) vanes can be varied to produce the desired boost pressure. At idle and during shutdown, the vanes are ----_____ closed?

A)70-75%"
B)80-85%"
C)90-95%
D)95-100%"

Question 44

In most engines, at what vehicle speed do the VGT (variable-geometry turbocharger) vanes close to provide the engine with a natural retarding force that more closely resembles a gasoline-fueled engine with a throttle plate?

A)10-20 mph"
B)3-6 mph"
C)5-10 mph
D)6-8 mph"

Question 45

Technician A says that coolant passageways through the turbocharger housing are used to keep the turbocharger bearings and other parts cooled when the engine is running. Technician B says that coolant passageways are used primarily to circulate coolant after the engine has been shut off. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 46

While two technicians are discussing series turbocharging, Technician A says the high-pressure turbocharger has an exhaust bypass valve that prevents overspeeding. Technician B says the low-pressure turbocharger uses a waste gate to direct exhaust gases to the high-pressure turbocharger. Who is correct?

A)Technician A"
B)Technician B"
C)Both A and B
D)Neither A nor B"

Question 47

A "woofing" sound from the air intake when the engine is rapidly accelerated and decelerated is one symptom of a slow-responding actuator and this condition, known as turbocharger surge, produces a sound referred to as:

A)woofing"
B)chuggle"
C)slugging
D)chuffing"

Question 48

Technician A says that the calibration code on a Garrett electric actuator must match a specific engine calibration for the turbocharger to operate correctly. Technician B says that a sticking nozzle ring will eventually overload the electric motor in the VGT (variable-geometry turbocharger) actuator and cause it to burn out. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 49

Which of the following does NOT cause a vibration that is synchronized to specific engine speed?

A)Out of balance turbocharger"
B)Broken or bent connecting rod"
C)Out of balance or bent crankshaft
D)Dented vibration damper"

Question 50

When replacing motors and modules in the actuator, the ECM (Engine Control Module) is required to ________ to accurately adjust vane or the sliding nozzle's new position.

A)re-learn the actuator"
B)reprogram all factory settings"
C)update the EEPROM (electronically erasable programmable read only memory)
D)be replaced"

Question 51

Two technicians are explaining how to replace a VGT (variable-geometry turbocharger) actuator. Technician A says that you hold and shake the sector gear inside the turbocharger to check for excessive movement, which would indicate a failed bearing in the sector shaft. Technician B says that if the sector gear does not sweep freely, the turbocharger will need to be replaced. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"

Question 52

What continuously monitors the VGT (variable-geometry turbocharger) to detect any condition that could lead to potential increases in exhaust emissions?

A)FICM (fuel injection control module)"
B)ECM (engine control module)"
C)OBD (on-board diagnostic) monitors
D)BCM (body computer module)"

Question 53

Consider the operation of a single-sequential DualBoost turbocharger. What combination of air inlets and outlets are used?

A)One air inlet and two outlets."
B)Two air inlets and one outlet."
C)Two inlets and two outlets.
D)A dual path air inlet and bypass valve-regulated outlet."

Question 54

What diesel engine, code-named Scorpion Diesel, uses a unique, patented single-sequential turbocharger (SST)?

A)Ford's 6.7 L Power Stroke"
B)GM 6.6L Duramax"
C)Cummins 6.7: Six
D)Fiat V6 Diesel"

Question 55

Single-sequential turbocharger (SST) claims to have reduced the mass of the turbine wheel and accompanying inertia by up to:

A)20%"
B)30%"
C)40%
D)50%"

Question 56

Ford used this DualBoost Turbo turbocharger from 2011 until 2014, when it replaced it with a:

A)Garrett VGT (variable-geometry turbochargers)"
B)Holset VGT (variable-geometry turbochargers)"
C)Waste-gate turbocharger
D)Fixed turbocharger"

Question 57

Also known as aftercooling and intercooling, what system removes excess heat from the air, thereby charging the cylinders?

A)CAC (charge air cooling)"
B)EGR Cooler"
C)ATAAC (air-to-air charge air cooling)
D)JWAC (jacket water aftercooler)"

Question 58

High boost pressures produced by which of the following enable the use of late intake valve closing?

A)ATAAC (air-to-air charge air cooling)"
B)JWAC (jacket water aftercooler)"
C)Series turbocharging
D)VGT (variable-geometry turbocharger)"

Question 59

Which of the following use a mechanism to hold the intake valve open longer under high boost conditions so that the engine does not need to work as hard to compress air?

A)Otto cycle engines"
B)Miller cycle engines"
C)2-stroke cycle engines
D)4-stroke Otto cycle engines"

Question 60

Technician A says that a single-sequential turbocharger (SST) integrates four turbochargers into a single component. Technician B says that a single housing unit supports two compressor wheels, a configuration that reduces space requirements. Who is right?

A)A only"
B)B only"
C)Both A and B
D)Neither A nor B"