Deck 15: Fixed Geometry and Wastegated Turbochargers

Question 1

What is the primary function of a turbocharger?

A)It operates only as an engine brake.
B)It speeds up engine warm-up.
C)It supplies addtional intake air mass.
D)It enables the use of larger displacement engine.

Answer 1

B

Question 2

Which of the following reasons best explains how turbochargers maintain intake boost pressure (normalization) at high altitudes?

A)Greater exhaust heat from lean air-fuel mixtures at high altitudes.
B)Less resistance to compressor wheel rotation offered by lower-density air at high altitudes.
C)Greater pressure differential across the turbine wheel at high altitudes.
D)The use of a boost pressure sensor to provide closed-loop feedback control over intake pressure.

Answer 2

B

Question 3

Why is a barometric pressure sensor used on an electronically controlled, fixed-geometry-turbocharged diesel engine?

A)To increase boost pressure.
B)To lower air-fuel ratios.
C)To minimize exhaust smoke at high altitudes.
D)To prevent turbocharger overspeed.

Answer 3

D

Question 4

Technician A says that all engines lose power at higher altitudes due to lower air density. Technician B says that turbocharged diesel engines are an exception and that intake manifold air pressure remains the same regardless of altitude. Who is correct?

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

Question 5

Technician A says that turbocharging a diesel engine reduces most noxious emissions because the cylinder pressure is higher. Technician B says that turbocharging lowers emissions because it provides more air to completely burn fuel in the cylinders. Who is correct?

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

Question 6

Technician A says that a barometric pressure sensor on an electronically controlled diesel engine prevents fixed-geometry turbocharger damage caused by overspeeding. Technician B says that waste gates provide turbocharger overspeed protection. Who is correct?

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

Question 7

Which of the following is the most likely cause of bent and distorted turbocharger compressor blades?

A)Contact with a 1/4" (6 mm) nut.
B)Turbo overspeed.
C)Overheating.
D)Air cleaner sealing gasket ingestion.

Question 8

Which of the following features is characteristic of engines that use waste-gated turbochargers?

A)Less turbo lag.
B)Slower throttle response.
C)Reduced exhaust backpressure.
D)Greater power density at high speed and load conditions.

Question 9

Technician A says that turbocharging pressure in a diesel engine is limited by the threshold at which a diesel combustion chamber will begin to detonate. Technician B says that diesel turbocharger pressures are designed to match the air-fuel ratio requirements of the engine combustion system. Who is correct?

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

Question 10

Technician A says that fixed-geometry turbochargers that lack controls are designed to provide maximum boost pressure at rated speed or peak horsepower. Technician B says that a properly matched turbocharger will need to provide maximum boost pressure at the highest cylinder pressure, which is peak torque. 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 turbocharger lag is caused by the inertia of heavy compressor and turbine wheel assemblies. Technician B says turbocharger lag is caused by the slow buildup of fuel rate by the high-pressure injection system. Who is correct?

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

Question 12

Which of the following is the most likely cause of a pitted and worn turbocharger compressor wheel?

A)Water ingestion.
B)A turbocharger that's been in service for too long.
C)A leaking air induction system.
D)Parts of a rag or air filter gasket passing through the compressor wheel.

Question 13

Consider an on-highway diesel engine that has a precisely matched turbocharger. Under which of the following conditions should turbine speeds be greatest to achieve maximum engine output?

A)Peak horsepower.
B)Peak torque.
C)Low engine rpm.
D)High idle.

Question 14

Which of the following is changed when the diameter of a turbocharger turbine or compressor housing is increased?

A)A/R ratio.
B)Inducer diameter.
C)Exducer diameter.
D)Nozzle ring.

Question 15

Which of the following conditions is likely caused by the waste gate failing to close on a waste-gated turbocharger?

A)Turbo bearing failure.
B)Higher CO emissions.
C)Low power.
D)Excessive turbo slobber.

Question 16

Technician A says that if a turbocharger is disassembled and a new compressor wheel is installed, then the turbocharger will need to be balanced. Technician B says that a compressor wheel's light weight will not affect turbocharger operation one way or another. Who is correct?

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

Question 17

Technician A says that excessive wear on the thrust bearing will cause the compressor wheel to contact the compressor housing. Technician B says that only excessively worn center support bearings will allow the compressor wheel to contact the compressor housing. Who is correct?

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

Question 18

Which of the following conditions is likely caused by the failure of the waste gate to open on a waste-gated turbocharger?

A)Turbo bearing failure.
B)Higher carbon monoxide (CO) emissions.
C)Low power.
D)Excessive turbo slobber.

Question 19

Technician A says waste-gated turbochargers enable smaller displacement diesel engines to produce more power at low engine speeds. Technician B says waste gates prevent turbochargers from overspeeding at high speed and load conditions. Who is correct?

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

Question 20

Technician A says that an engine that uses two turbochargers could use compressor and turbine housings of two different sizes. Technician B says that an engine that uses two turbochargers could use identical turbochargers, which is referred to as a parallel turbocharged engine. Who is correct?

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

Question 21

Which of the following is NOT the result of an engine reaching a limit where the addition of more fuel produces no increase in power and cannot breathe in enough air?

A)Blue exhaust smoke"
B)Black exhaust smoke"
C)Decreasing fuel economy
D)High exhaust temperatures"

Question 22

Exhaust gas energy would normally vent directly to the atmosphere. Instead, which of the following can recover some of that energy to improve engine efficiency?

A)Supercharger"
B)Nitrous oxide"
C)Vent tube
D)Turbochargers"

Question 23

Technician A says that a supercharger uses energy from exhaust gases to turn a turbine wheel, which causes a compressor impeller to pressurize air for combustion. Technician B says that every engine reaches a limit where the addition of more fuel produces no increase in power because it cannot breathe in enough air. Who is right?

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

Question 24

When a turbocharger turns at high speed, the compressor can supply air to the combustion chambers at pressure above:

A)15.7 psi"
B)12.7 psi"
C)13.7 psi
D)14.7 psi"

Question 25

Why is a barometric pressure sensor used on an electronically controlled, fixed-geometry-turbocharged diesel engine?

A)To increase boost pressure."
B)To lower air-fuel ratios."
C)To minimize exhaust smoke at high altitudes.
D)To prevent turbocharger overspeed."

Question 26

Technician A says that turbocharging a diesel engine reduces most noxious emissions because the cylinder pressure is higher. Technician B says that turbocharging lowers emissions because it provides more air to completely burn fuel in the cylinders. Who is correct?

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

Question 27

Two technicians are discussing turbocharger operation. Technician A says that turbochargers are used on diesel engines to improve their power output while decreasing engine size and displacement. Technician B says that turbochargers enhance engine efficiency. Who is right?

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

Question 28

A restricted, undersized, or otherwise damaged exhaust system is easily overlooked when investigating complaints about:

A)loss of power under load at high speed"
B)loss of power under load at low speed"
C)loss of power with no load at high speed
D)loss of power with no load at low speed"

Question 29

Which of the following features is characteristic of engines that use waste-gated turbochargers?

A)Less turbo lag."
B)Slower throttle response."
C)Reduced exhaust backpressure.
D)Greater power density at high speed and load conditions."

Question 30

What causes the pressure to drive the turbine wheel of the turbocharger?

A)Temperature of unexpanded exhaust gas"
B)Intake pressure"
C)Engine compression
D)Energy of unexpanded exhaust gas"

Question 31

Which of the following can prevent exhaust gas from expanding?

A)Narrow exhaust manifold runners"
B)Wide exhaust manifold runners"
C)Energy of unexpanded exhaust gas
D)Exhaust pressure"

Question 32

What other condition can occur when the air to support combustion during turbo lag is not adequate?

A)White smoke"
B)Black smoke"
C)Blue smoke
D)Grey smoke"

Question 33

Technician A says that turbocharger lag is caused by the inertia of heavy compressor and turbine wheel assemblies. Technician B says turbocharger lag is caused by the slow buildup of fuel rate by the high-pressure injection system. Who is correct?

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

Question 34

Which of the following is NOT a disadvantage of fixed-geometry turbochargers?

A)Produces little boost at low speeds"
B)Air-fuel ratios are also low at low-speed operation"
C)High PM, HC, and CO emissions
D)Air-fuel ratios are high at low-speed operation"

Question 35

Turbochargers are designed to turn faster at lower engine load factors, increasing power density, or power output per liter (or cubic inch) of displacement, of small-bore engines at low speed while minimizing:

A)turbocharger lag"
B)horsepower"
C)torque lag
D)ignition delay"

Question 36

Smaller displacement engines will not need to turn as fast to produce what is known as:

A)speed density"
B)power density"
C)torque ratio
D)power ratio"

Question 37

Consider an on-highway diesel engine that has a precisely matched turbocharger. Under which of the following conditions should turbine speeds be greatest to achieve maximum engine output?

A)Peak horsepower."
B)Peak torque."
C)Low engine rpm.
D)High idle."

Question 38

Technician A says that if a turbocharger is disassembled and a new compressor wheel is installed, then the turbocharger will need to be balanced. Technician B says that a compressor wheel's light weight will not affect turbocharger operation one way or another. Who is correct?

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

Question 39

The inlet to the turbine is located on the outside radius of the turbine housing and attaches to the:

A)exhaust manifold"
B)intake manifold"
C)DPF (diesel particulate filter)
D)vehicle exhaust pipe"

Question 40

What is shaped like the turbine housing but with the opposite direction of gas flow?

A)Compressor housing"
B)Vehicle exhaust pipe"
C)Intake manifold
D)DPF (diesel particulate filter)"

Question 41

Technician A says waste-gated turbochargers enable smaller displacement diesel engines to produce more power at low engine speeds. Technician B says waste gates prevent turbochargers from overspeeding at high speed and load conditions. Who is correct?

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

Question 42

If you find a worn compressor/turbine wheel shaft or bearings, which of the following should be done?

A)Replace the turbocharger"
B)Shim the compressor shaft"
C)Shim the turbine shaft
D)Rebuild the turbocharger"

Question 43

Two technicians are explaining how to measure turbocharger radial bearing clearance. Technician A says that while rotating the turbine wheel, you check for any binding or roughness. Technician B says that any contact between the compressor wheel and housing indicates that the center support bearings are excessively worn. Who is right?

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

Question 44

To measure center support bearing wear, push down on the compressor wheel with moderate finger pressure while inserting the thickest feeler blade that will fit between the compressor wheel and the:

A)turbine wheel"
B)compressor bearings"
C)compressor Shaft
D)compressor housing"

Question 45

Two technicians are explaining how to measure waste-gate movement. Technician A says that you apply a calibrated amount of air pressure to the waste-gate actuator, usually around 100 psi. Technician B says that you compare maximum boost pressure to the manufacturer's specifications to determine waste-gate operation threshold. Who is right?

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

Question 46

When gas temperatures increase, molecules spread farther apart, so the gas loses:

A)pressure"
B)space"
C)temperature
D)density"

Question 47

If intake or underhood intake air temperature is 75°F (24°C) at atmospheric pressure (15 psi [103 kPa] at sea level), the turbo outlet temperature will be:

A)185°F"
B)285°F"
C)385°F
D)485°F"

Question 48

Power decreases 1% for every _____ above 90°F.

A)05°F"
B)10°F"
C)20°F
D)30°F"

Question 49

Increases in charge air temperatures result in higher combustion chamber temperatures, which increase the production of:

A)NOx (oxides of nitrogen)"
B)CO (carbon monoxide)"
C)CO₂ (carbon dioxide)
D)HC (hydrocarbons)"

Question 50

Which of the following is NOT a benefit of charge air cooling?

A)Increases air density and oxygen content"
B)Provides additional air mass for cooling valves and pistons"
C)Denser, cooler air improves fuel economy
D)Major improvement in power"

Question 51

Efficient and effective heat transfer is necessary to prevent:

A)low emissions"
B)engine damage"
C)ignition delay
D)combustion delay"

Question 52

A JWAC (jacket water aftercooler) is capable of lowering the turbocharger boost air temperature from approximately 300°F to approximately:

A)200°F"
B)250°F"
C)100°F
D)150°F"

Question 53

The Ford 6.7 L Power Stroke uses a(n):

A)liquid CAC (charge air cooler)"
B)standard CAC (charge air cooler)"
C)JWAC (jacket water aftercooler)
D)intake manifold jacket water aftercooler"

Question 54

Technician A says that when servicing the cooling system of an engine that uses a JWAC (jacket water aftercooler), bleeding air from the cooler is not necessary. Technician B says that the JWAC is a low point in the cooling system, so air can become trapped in the cooler and prevent proper functioning. Who is right?

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

Question 55

Moving the heated charge air through an ATAAC can drop the temperature from higher than 400°F to:

A)80°F-90°F"
B)90°F-110°F"
C)110°F-120°F
D)120°F-140°F"

Question 56

The ECM will disconnect which of the following devices when the engine is under boost pressure and when intake air temperatures need to be lowered?

A)Electric air intake heaters"
B)Glow plugs"
C)Injectors
D)DPF (diesel particulate filter)"

Question 57

A CAC (charge-air-cooler) system pressure drop is measured with a:

A)slack-tube mercury manometer"
B)slack-tube water manometer"
C)digital flow meter
D)digital multimeter"

Question 58

Technician A says that small cracks do not warrant replacing a CAC (charge-air-cooler) system, because dirt ingestion into the engine through a crack is not likely when a cooler is pressurized. Technician B says that many manufacturers do not recommend replacing the cooler if the leak is small. Who is right?

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

Question 59

Two technicians are describing pressure testing a CAC (charge-air-cooler). Technician A says that you connect an air pressure regulator to the test adapter plug, and pressurize the cooler to 30 psi. Technician B says that you shut off the air pressure supply to the regulator, and count the number of seconds it takes for the cooler to drop 15 psi. Who is right?

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

Question 60

After a turbocharger failure or after a CAC (charge-air-cooler) core has become internally restricted, which of the following is done?

A)Blow out the core with compressed air"
B)Run a wire through the core"
C)Back-flush cooler cores
D)Place the CAC (charge-air-cooler)"