ASVAB Auto and Shop: Engine Systems and Repair 2 — Questions and Answers
Question 1: What is the purpose of the camshaft in a 4-stroke engine?
- Pump fuel to the injectors
- Open and close intake and exhaust valves (Correct answer)
- Spin the alternator belt
- Control ignition timing directly
Correct answer: Open and close intake and exhaust valves
The camshaft uses lobes to push on valve lifters, opening and closing the intake and exhaust valves at precisely timed intervals.
Question 2: A car engine runs hot and the temperature gauge reads high. The coolant level is normal. What is the most likely cause?
- Clogged fuel filter
- Faulty thermostat stuck closed (Correct answer)
- Worn brake pads
- Low power steering fluid
Correct answer: Faulty thermostat stuck closed
A thermostat stuck in the closed position prevents coolant from circulating through the radiator, causing the engine to overheat.
Question 3: Which engine component seals the combustion chamber between the cylinder head and engine block?
- Valve stem seal
- Head gasket (Correct answer)
- Piston ring
- Crankshaft seal
Correct answer: Head gasket
The head gasket forms a seal between the cylinder head and the engine block to contain combustion pressure and prevent coolant or oil leaks.
Question 4: What does a PCV (Positive Crankcase Ventilation) valve do?
- Pressurizes the fuel tank
- Vents crankcase gases back into the intake manifold (Correct answer)
- Controls valve timing
- Regulates oil pressure
Correct answer: Vents crankcase gases back into the intake manifold
The PCV valve recirculates blow-by gases from the crankcase back into the intake manifold to be burned, reducing emissions.
Question 5: An engine has low compression in one cylinder. What is the most likely cause?
- Clogged air filter
- Worn or damaged piston rings (Correct answer)
- Dirty fuel injector
- Weak battery
Correct answer: Worn or damaged piston rings
Worn piston rings allow combustion gases to bypass the piston and escape into the crankcase, reducing compression in that cylinder.
Question 6: What type of engine uses glow plugs instead of spark plugs?
- Rotary engine
- Two-stroke gasoline engine
- Diesel engine (Correct answer)
- Hybrid electric engine
Correct answer: Diesel engine
Diesel engines use glow plugs to preheat the combustion chamber, since they ignite fuel by compression rather than a spark.
Question 7: What is the function of the crankshaft in an engine?
- Convert rotational motion into linear motion
- Convert linear piston motion into rotational motion (Correct answer)
- Drive the water pump directly
- Control fuel delivery timing
Correct answer: Convert linear piston motion into rotational motion
The crankshaft converts the up-and-down (linear) motion of the pistons into the rotational motion that ultimately drives the vehicle.
ASVAB Auto and Shop: Engine Systems and Repair 2
What is the purpose of the camshaft in a 4-stroke engine?