DTC DTC Air Intake and Turbocharger Systems

Question 1

What is the primary purpose of the charge air cooler (intercooler) in a turbocharged diesel engine?

Accepted Answer

To reduce the temperature of compressed air before it enters the intake manifold

Answer

To cool the engine coolant before it enters the radiator

Answer

To lower the exhaust gas temperature before the turbocharger

Answer

To cool the turbocharger center housing

Question 2

A diesel engine exhibits black smoke at full load accompanied by lower than normal boost pressure. Which component is MOST likely at fault?

Accepted Answer

Worn or damaged turbocharger

Answer

Clogged fuel injectors

Answer

Faulty EGR valve stuck open

Answer

Restricted exhaust back-pressure sensor

Question 3

When inspecting a turbocharger for shaft play, what type of movement indicates a worn center bearing?

Accepted Answer

Excessive radial (side-to-side) play

Answer

Rotational play only

Answer

Excessive axial (end-to-end) play only

Answer

No detectable movement at all

Question 4

What does a Variable Geometry Turbocharger (VGT) use to control boost pressure at different engine speeds?

Accepted Answer

Adjustable vanes in the turbine housing that redirect exhaust gas flow

Answer

A wastegate valve that bypasses exhaust gases around the turbine

Answer

A bypass valve on the compressor outlet

Answer

A mechanically driven supercharger that supplements the turbo

Question 5

A technician notices oil in the intake air piping between the turbocharger and the charge air cooler. What is the MOST likely cause?

Accepted Answer

Worn turbocharger compressor seal allowing oil to be ingested

Answer

Overfilled engine oil level causing crankcase pressure

Answer

Clogged crankcase ventilation (breather) tube

Answer

Defective positive crankcase ventilation (PCV) valve

Question 6

What is the purpose of the wastegate on a conventional turbocharger?

Accepted Answer

To limit maximum boost pressure by routing excess exhaust gas around the turbine wheel

Answer

To allow exhaust gases to bypass the diesel particulate filter during regeneration

Answer

To control the EGR rate by metering exhaust back into the intake

Answer

To vent crankcase pressure to the atmosphere

Question 7

Which air filter restriction measurement tool is most commonly used to determine when a diesel engine air filter requires replacement?

Accepted Answer

A manometer or restriction indicator on the air cleaner housing

Answer

A vacuum gauge connected to the crankcase breather

Answer

A pressure gauge on the turbocharger compressor outlet

Answer

An infrared thermometer measuring filter temperature