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

Turbocharger surge occurs when the compressor wheel operates beyond its surge line — typically at low airflow conditions — causing a cyclic breakdown and recovery of airflow that produces a characteristic repetitive sound.

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

Boost pressure is the pressurized air delivered to the engine cylinders, so the gauge is connected at the intake manifold or the air piping after the charge air cooler to measure actual delivered boost.

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

The contaminated charge air cooler must be replaced because residual oil deposits restrict airflow and can be ingested into the engine; the root cause (typically a turbo seal or crankcase ventilation issue) must also be corrected.

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

Pre-lubricating the turbocharger by cranking without starting, and then idling before applying load, ensures the center bearing receives adequate oil pressure before the turbine spins at high speed, preventing dry-start damage.

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

An air leak on the pressurized intake side causes boost pressure loss, resulting in reduced power output; the escaping compressed air often produces a hissing or whistling noise under load.

DTC - Diesel Technician Certification Practice Test

DTC - Diesel Technician Certification Practice Test

DTC DTC Air Intake and Turbocharger Systems 2