Light Vehicle Diesel Engines Flashcards

What is the main advantage of using a variable geometry turbocharger (VGT) on a light vehicle diesel?

Answer: Better boost response across a wide RPM range

A VGT adjusts vane geometry to optimize boost at both low and high RPM, reducing turbo lag and improving response.

A DPF differential pressure sensor reads abnormally high. What does this most likely indicate?

Answer: The DPF is heavily loaded or clogged

High differential pressure across the DPF indicates restriction from accumulated soot or ash requiring regeneration or replacement.

Why must engine oil meeting low-SAPS specifications be used in diesels equipped with a DPF?

Answer: To minimize ash that clogs the DPF

Low-SAPS (sulfated ash, phosphorus, sulfur) oils reduce ash buildup that permanently accumulates in and clogs the DPF.

An engine repeatedly enters limp mode after attempted regenerations. Besides the DPF, what should be evaluated?

Answer: EGR, turbo, and injector performance contributing to high soot

Excessive soot causing failed regens often stems from underlying issues like faulty injectors, EGR, or turbo problems.

What is the purpose of pilot injection in a modern common rail diesel?

Answer: Reduce combustion noise and smooth pressure rise

A small pilot injection before the main event softens the pressure rise, reducing diesel knock and combustion harshness.

A glow plug fails as a short circuit. What is a likely consequence for the system?

Answer: Blown fuse or controller fault and a glow plug warning

A shorted glow plug can overload the glow plug control module circuit, blowing a fuse and setting a fault.

When diagnosing low common rail pressure, which component is commonly tested for excessive internal leakage (return flow)?

Answer: Fuel injectors

Worn injectors can leak excessive fuel back to the return line, dropping rail pressure; a return-flow test identifies the faulty unit.