ASE Practice Test #3 2 — Questions and Answers
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?
- Weak battery
- 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 (Correct answer)
- Low coolant level
- Worn starter motor brushes
Correct 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
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?
- To add fresh air directly into the combustion chamber
- 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 (Correct answer)
- To pressurize the crankcase for better oil distribution
- To cool the engine oil by circulating fresh air through the oil pan
Correct 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
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?
- A leaking brake caliper piston seal
- 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 (Correct answer)
- Low brake fluid in the reservoir
- Warped front brake rotors
Correct 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
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?
- Normal combustion that occurs before TDC
- 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 (Correct answer)
- A loose engine mount causing a knocking noise
- Fuel injector backfire into the intake manifold
Correct 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
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?
- Outside micrometer
- Dial bore gauge (cylinder bore gauge) (Correct answer)
- Vernier caliper
- Feeler gauge
Correct answer: Dial bore gauge (cylinder bore gauge)
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.
Question 6: When should a torque-to-yield (TTY) fastener be replaced rather than reused?
- Only when visually damaged
- After every removal — TTY fasteners are designed to be used once and are permanently deformed beyond their elastic limit during initial tightening; reuse reduces clamping force and risks fastener failure (Correct answer)
- TTY fasteners can be reused up to 3 times
- Only when the threads are visually stripped
Correct answer: After every removal — TTY fasteners are designed to be used once and are permanently deformed beyond their elastic limit during initial tightening; reuse reduces clamping force and risks fastener failure
Torque-to-yield fasteners (commonly used for cylinder head bolts, connecting rod bolts, and main bearing cap bolts) are designed to stretch plastically during tightening to provide precise, consistent clamping force. Once stretched past the elastic limit (yield point), the fastener has permanently deformed and cannot achieve the same clamping force if retightened. Reusing TTY fasteners risks insufficient clamping force (head gasket leak) or fastener failure under load. OEM specifications always specify replacement of TTY fasteners.
ASE Practice Test #3 2
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?