ASVAB Auto and Shop: Engine Systems and Repair 3 — Questions and Answers
Question 1: What does an engine's displacement measurement (e.g., 2.0L) refer to?
- The engine's oil capacity in liters
- The total volume swept by all pistons in one complete cycle (Correct answer)
- The fuel tank capacity
- The coolant system volume
Correct answer: The total volume swept by all pistons in one complete cycle
Engine displacement is the total volume swept by all pistons moving from bottom dead center to top dead center in one revolution.
Question 2: A vehicle produces white smoke from the exhaust on a warm day. What does this most likely indicate?
- Rich fuel mixture
- Coolant burning in the combustion chamber (Correct answer)
- Clogged catalytic converter
- Worn brake rotors
Correct answer: Coolant burning in the combustion chamber
White smoke from the exhaust typically indicates coolant is leaking into the combustion chamber, often due to a blown head gasket.
Question 3: Which of the following best describes valve overlap in an engine?
- When two valves in the same cylinder open simultaneously
- When the intake valve closes before the exhaust valve opens
- When both intake and exhaust valves are partially open at the same time (Correct answer)
- When the camshaft and crankshaft rotate at the same speed
Correct answer: When both intake and exhaust valves are partially open at the same time
Valve overlap is the brief period at the end of the exhaust stroke and beginning of the intake stroke when both valves are partially open simultaneously.
Question 4: What is the primary purpose of engine oil in a vehicle?
- Cool the combustion chamber directly
- Lubricate moving parts to reduce friction and wear (Correct answer)
- Improve fuel combustion efficiency
- Seal the combustion chamber
Correct answer: Lubricate moving parts to reduce friction and wear
Engine oil lubricates the moving metal components of the engine to minimize friction, reduce wear, and help dissipate heat.
Question 5: What is detonation (engine knock) in a gasoline engine?
- Premature ignition of the air-fuel mixture before the spark plug fires (Correct answer)
- Normal combustion proceeding from the spark plug
- Exhaust gas recirculating into the intake
- Carbon buildup on spark plug tips
Correct answer: Premature ignition of the air-fuel mixture before the spark plug fires
Detonation (knock) occurs when the air-fuel mixture ignites prematurely or unevenly in the cylinder, causing a characteristic knocking sound.
Question 6: A timing belt breaks while the engine is running. What is likely to happen in an interference engine?
- The engine will idle roughly but keep running
- Pistons and valves will collide, causing severe damage (Correct answer)
- The cooling system will overheat immediately
- The fuel injectors will stop firing
Correct answer: Pistons and valves will collide, causing severe damage
In an interference engine, the piston and valve paths overlap, so a broken timing belt causes pistons to strike open valves, causing catastrophic engine damage.
Question 7: What tool is used to measure the pressure inside an engine's cylinders?
- Torque wrench
- Compression tester (Correct answer)
- Vacuum gauge
- Feeler gauge
Correct answer: Compression tester
A compression tester is threaded into each spark plug hole to measure the peak pressure developed when the piston moves up on the compression stroke.
ASVAB Auto and Shop: Engine Systems and Repair 3
What does an engine's displacement measurement (e.g., 2.0L) refer to?