ASE Light Vehicle Diesel Engines 2

Question 1

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

Accepted Answer

High-pressure fuel pump

Answer

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

Question 2

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

Accepted Answer

Glow plug system

Answer

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

Question 3

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

Accepted Answer

Burn off accumulated soot

Answer

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

Question 4

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

Accepted Answer

Incomplete combustion from too much fuel or too little air

Answer

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

Question 5

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

Accepted Answer

Crankshaft position sensor

Answer

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

ASE Practice Test