Light Vehicle Diesel Engines Flashcards

In a common rail diesel injection system, what component is primarily responsible for generating the extremely high fuel pressure?

Answer: High-pressure fuel pump

The high-pressure pump pressurizes fuel and feeds the common rail, while the lift pump only supplies low-pressure fuel from the tank.

A diesel engine has hard starting when cold but runs fine once warm. Which system should you inspect first?

Answer: Glow plug system

Glow plugs preheat the combustion chamber for cold starts, so a faulty glow plug system causes cold-start difficulty that disappears when warm.

What is the purpose of the diesel particulate filter (DPF) regeneration process?

Answer: Burn off accumulated soot

Regeneration raises exhaust temperature to oxidize trapped soot into ash and gases, restoring DPF flow.

Excessive black smoke from a diesel under load most commonly indicates which condition?

Answer: Incomplete combustion from too much fuel or too little air

Black smoke results from unburned fuel, typically due to over-fueling, a restricted air intake, or a failing turbocharger.

Which sensor signals the PCM about the position and speed of the crankshaft for diesel injection timing?

Answer: Crankshaft position sensor

The crankshaft position sensor provides RPM and TDC reference data essential for precise injection timing.

What does a glow plug 'wait-to-start' lamp indicate to the driver?

Answer: Glow plugs are still preheating the cylinders

The lamp stays on while the glow plugs heat the combustion chambers and goes out when it is safe to crank.

Why is using clean, properly filtered fuel especially critical in modern high-pressure common rail diesels?

Answer: Tight injector tolerances are easily damaged by contaminants

Common rail injectors operate with micron-level clearances, so water or particulates can quickly cause wear and failure.