Engine and Fuel Systems Flashcards

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

Answer: Incomplete fuel combustion due to cold engine

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

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

Answer: High-pressure accumulator rail

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

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

Answer: Restricted fuel filter

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

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

Answer: Worn or damaged rings or valves in that cylinder

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

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

Answer: Cylinder leakdown test

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

What is the purpose of the fuel return line on a diesel injection system?

Answer: To return excess fuel and cool the injectors back to the tank

The fuel return line carries excess fuel and absorbed heat from the injectors back to the fuel tank, cooling the injection components.

A truck's engine idles smoothly but stumbles when throttle is applied quickly. On a diesel, this most likely indicates:

Answer: Turbocharger lag or restricted intake

Stumbling under rapid throttle application in a turbocharged diesel often results from turbo lag or a restricted air intake causing a momentary lean condition.