310T Engine and Fuel Systems 3

Question 1

A diesel engine exhibits excessive white smoke at startup that clears after warm-up. What is the most likely cause?

Accepted Answer

Incomplete fuel combustion due to cold engine

Answer

White smoke at cold startup is typically unburned fuel vapor from incomplete combustion that dissipates as the engine reaches operating temperature.

Question 2

On a common rail diesel fuel system, what component maintains system pressure between injection events?

Accepted Answer

High-pressure accumulator rail

Answer

The high-pressure accumulator rail stores pressurized fuel and dampens pressure fluctuations to maintain consistent injection pressure.

Question 3

Which condition would cause a diesel engine to run rough and produce black smoke under load?

Accepted Answer

Restricted fuel filter

Answer

A restricted fuel filter starves injectors of fuel at high demand, causing incomplete combustion and black smoke under load.

Question 4

When performing a diesel engine compression test, a reading of 380 psi on one cylinder versus 480 psi on all others indicates:

Accepted Answer

Worn or damaged rings or valves in that cylinder

Answer

A cylinder reading more than 10% below the average indicates internal sealing problems such as worn rings, damaged valves, or a blown head gasket.

Question 5

A technician notices the crankcase pressure is excessive and oil is pushed out through seals. What test should be performed first?

Accepted Answer

Cylinder leakdown test

Answer

A cylinder leakdown test identifies which cylinders are passing combustion gases into the crankcase, causing excessive blow-by pressure.

(310t) Truck and Coach Technician Certification Practice Test