ASE Light Vehicle Diesel Engines 3

Question 1

What is the primary function of the exhaust gas recirculation (EGR) system on a diesel engine?

Accepted Answer

Reduce NOx emissions by lowering combustion temperature

Answer

EGR routes inert exhaust gas back into the intake to lower peak combustion temperatures and reduce nitrogen oxide formation.

Question 2

A turbocharged diesel shows low boost and sluggish acceleration. Which component should you check for a stuck or leaking condition?

Accepted Answer

Turbocharger and its boost control/wastegate

Answer

Low boost is commonly caused by a failing turbo, leaking charge pipes, or a malfunctioning wastegate/VGT actuator.

Question 3

What fluid is injected into the exhaust stream in an SCR (selective catalytic reduction) system?

Accepted Answer

Diesel exhaust fluid (urea/DEF)

Answer

DEF (a urea-water solution) reacts in the SCR catalyst to convert NOx into nitrogen and water.

Question 4

On a diesel engine, what is the most likely cause of a 'no-start' with normal cranking speed and no smoke?

Accepted Answer

No fuel delivery or loss of fuel pressure

Answer

If the engine cranks normally but never fires and produces no smoke, fuel is likely not reaching the cylinders.

Question 5

Which measurement is most useful for diagnosing a diesel cylinder with low power contribution?

Accepted Answer

Compression test

Answer

A compression test reveals worn rings, valves, or head gasket issues that reduce a cylinder's combustion sealing.

ASE Practice Test