ASE Practice Test #3 2

Question 1

A vehicle has intermittent no-start that the customer describes as occurring only when the engine is hot. The engine cranks but does not start when hot. What should the technician suspect?

Accepted Answer

A heat-sensitive component failure such as a crankshaft position sensor, ignition module, or fuel pump that breaks down when hot and recovers when cool

Answer

Hot no-start conditions (starts fine cold, won't start when hot) are classic symptoms of thermally-sensitive electronic or electrical component failures. Electronic components (ignition modules, CKP sensors, camshaft position sensors, ECMs) can fail when hot and recover as they cool. Fuel pumps can fail hot due to heat-soaked vapor or worn motor windings. Attempting to restart immediately (before cooling) allows the technician to use scan tools to check for sensor signals that are absent when the fault is active.

Question 2

What is the purpose of the PCV (Positive Crankcase Ventilation) system in a gasoline engine?

Accepted Answer

To ventilate the crankcase by drawing blow-by gases (past the piston rings) back through the intake manifold for combustion, preventing pressure buildup and reducing hydrocarbon emissions

Answer

During engine operation, combustion gases blow past piston rings into the crankcase (blow-by). Without ventilation, these gases build pressure, force oil past seals, and contaminate the oil with fuel and water vapor. The PCV valve allows the intake manifold vacuum to draw these gases out of the crankcase, through the valve, and into the intake for combustion. This eliminates crankcase pressure, reduces emissions, and extends oil life. A stuck-closed PCV valve causes oil leaks and excessive crankcase pressure.

Question 3

A vehicle has a spongy brake pedal that improves after pumping multiple times. What is the MOST likely cause?

Accepted Answer

Air in the brake hydraulic system — compressible air causes the spongy feeling; pumping pushes fluid more firmly against the air bubble, temporarily improving pedal feel

Answer

Brake fluid is incompressible, so a properly bled system should have a firm pedal. Air is compressible. When air is trapped in a brake line or caliper, the pedal compresses the air before engaging the brakes, creating a spongy feel. Pumping the pedal temporarily increases hydraulic pressure past the air pocket, improving feel until the air redistributes. A thorough brake bleed (using pressure bleeding, vacuum bleeding, or the two-person method) removes the air and restores a firm pedal. The source of air entry must also be identified.

Question 4

What is "detonation" (engine knock) in a gasoline engine, and what are the primary causes?

Accepted Answer

Abnormal, spontaneous ignition of the end-gas charge ahead of the spark-ignited flame front, creating a pressure spike — caused by low-octane fuel, advanced timing, carbon deposits, or excessive cylinder temperature

Answer

Detonation (knock) occurs when the mixture of air and fuel in the cylinder ignites spontaneously due to heat and pressure before the normal spark-initiated flame front reaches it. Two flame fronts collide, creating a sharp pressure spike (knock). Causes include too-low octane fuel (insufficient resistance to spontaneous ignition), ignition timing too far advanced, excessive compression, carbon deposits raising effective compression, or intake charge temperature too high. Modern ECMs use knock sensors to retard timing when detonation is detected, protecting the engine.

Question 5

Which tool is used to measure the inside diameter of a cylinder bore for wear and out-of-round condition?

Accepted Answer

Dial bore gauge (cylinder bore gauge)

Answer

A dial bore gauge (also called a cylinder bore gauge) is the precision instrument used to measure cylinder bore diameter and detect taper (wear more at the top than bottom) and out-of-round (different diameters 90° apart). It is set to a reference with an outside micrometer, then inserted into the bore and rocked to find the minimum reading (indicating the true diameter). Multiple measurements at different depths and orientations map the wear pattern of the cylinder.