Light Vehicle Diesel Engines Flashcards

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

Answer: Reduce NOx emissions by lowering combustion temperature

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

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

Answer: Turbocharger and its boost control/wastegate

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

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

Answer: Diesel exhaust fluid (urea/DEF)

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

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

Answer: No fuel delivery or loss of fuel pressure

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

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

Answer: Compression test

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

What does a clogged or saturated fuel filter typically cause in a diesel engine?

Answer: Power loss and stalling under load

A restricted fuel filter starves the engine of fuel, causing hesitation, power loss, and stalling especially under heavy load.

Why do diesel engines compress air to a much higher ratio than gasoline engines?

Answer: Heat of compression ignites the fuel without a spark

Diesels rely on compression-ignition, where high compression heats the air enough to ignite injected fuel without a spark plug.