DTC DTC Air Intake and Turbocharger Systems 2

Question 1

What condition can cause a turbocharger to 'surge,' producing a repetitive whooshing or cyclical noise?

Accepted Answer

Compressor wheel operating in an unstable flow region due to low airflow demand

Answer

Excessive boost pressure from a stuck-closed wastegate

Answer

A partially blocked air filter restricting compressor inlet flow

Answer

A cracked charge air cooler allowing boost to escape

Question 2

When performing a boost pressure test on a turbocharged diesel, where should the pressure gauge be connected?

Accepted Answer

At the intake manifold or the charge air cooler outlet pipe

Answer

At the turbocharger turbine inlet (exhaust side)

Answer

At the crankcase breather outlet

Answer

At the fuel return line

Question 3

A diesel technician finds the charge air cooler core is clogged with oil residue internally. What is the CORRECT repair procedure?

Accepted Answer

Replace the charge air cooler and diagnose the source of the oil contamination before reinstalling a new unit

Answer

Flush the charge air cooler with solvent, reinstall, and monitor for further contamination

Answer

Leave the charge air cooler in place and repair the turbocharger seal only

Answer

Replace only the turbocharger without cleaning the charge air cooler

Question 4

What is the recommended procedure immediately after installing a new or rebuilt turbocharger before starting the engine?

Accepted Answer

Pre-lube the turbocharger center bearing by cranking the engine without starting, then let the engine idle before applying load

Answer

Install the turbocharger, start the engine immediately, and idle at high RPM to seat the bearings

Answer

Fill the turbocharger oil inlet port with clean engine oil, then start and immediately load the engine

Answer

Remove the oil drain line, fill with gear oil, reinstall, then start normally

Question 5

Which symptom would MOST likely indicate an air leak between the turbocharger compressor outlet and the intake manifold?

Accepted Answer

Low power, lower-than-normal boost, and possible hissing noise under load

Answer

Excessive black exhaust smoke at all engine speeds

Answer

Blue exhaust smoke at startup only

Answer

Low power with white exhaust smoke and low boost pressure

Question 6

In a diesel engine with a two-stage turbocharger system, what is the function of the low-pressure (LP) turbocharger?

Accepted Answer

To provide the initial compression stage, feeding pre-compressed air into the high-pressure compressor

Answer

To compress exhaust gases before they enter the high-pressure turbine

Answer

To regulate EGR flow between the two compressor stages

Answer

To act as a wastegate for the high-pressure turbocharger

Question 7

What is the most likely cause of blue-white smoke from a diesel engine that occurs primarily at idle and clears up at higher engine speeds?

Accepted Answer

Worn turbocharger seals allowing oil to be drawn into the intake under low-boost vacuum

Answer

Overfueling caused by a stuck-open injector

Answer

Coolant leaking past a failed head gasket into the combustion chamber

Answer

A clogged diesel particulate filter causing excess back pressure