ASVAB Auto and Shop: Engine Systems and Repair 5 — Questions and Answers
Question 1: What is the purpose of the exhaust gas recirculation (EGR) system?
- Increase fuel vaporization
- Reduce NOx emissions by recirculating a portion of exhaust gas into the intake (Correct answer)
- Cool the exhaust manifold
- Improve combustion efficiency at high RPM
Correct answer: Reduce NOx emissions by recirculating a portion of exhaust gas into the intake
The EGR system recirculates a small amount of exhaust gas back into the intake to lower combustion temperature, reducing harmful nitrogen oxide (NOx) emissions.
Question 2: When replacing a timing chain, what additional component should typically be replaced at the same time?
- Alternator
- Timing chain tensioner and guides (Correct answer)
- Throttle body
- Fuel pressure regulator
Correct answer: Timing chain tensioner and guides
Tensioners and guides wear along with the timing chain, so replacing them together prevents premature chain failure after a fresh installation.
Question 3: What does a higher compression ratio in a gasoline engine generally indicate?
- Greater tolerance for low-octane fuel
- Higher potential power output but requiring higher-octane fuel (Correct answer)
- Less efficient combustion
- Lower operating temperatures
Correct answer: Higher potential power output but requiring higher-octane fuel
Higher compression ratios extract more energy from combustion, increasing power output, but require higher-octane fuel to prevent detonation.
Question 4: What type of valve train arrangement has the camshaft mounted directly in the cylinder head?
- Overhead valve (OHV)
- Overhead camshaft (OHC) (Correct answer)
- Flathead (side valve)
- Pushrod with rocker arms
Correct answer: Overhead camshaft (OHC)
In an overhead camshaft (OHC) design, the camshaft sits in the cylinder head, operating valves directly or via short rocker arms for improved high-RPM performance.
Question 5: A car's engine oil appears milky or frothy on the dipstick. What does this indicate?
- The oil is overdue for a change
- Coolant has mixed with the engine oil, likely due to a head gasket failure (Correct answer)
- The engine is burning oil excessively
- The oil is too cold to circulate properly
Correct answer: Coolant has mixed with the engine oil, likely due to a head gasket failure
Milky, frothy oil indicates that coolant has entered the oil system, which typically results from a blown head gasket or cracked engine block.
Question 6: What is the purpose of balancing shafts in some engines?
- Drive the oil pump at twice crankshaft speed
- Counteract vibrations caused by the firing order of the pistons (Correct answer)
- Synchronize the camshaft to the crankshaft
- Prevent the crankshaft from flexing
Correct answer: Counteract vibrations caused by the firing order of the pistons
Balance shafts spin with counterweights that cancel out the secondary vibrations produced by the pistons' reciprocating motion, especially in 4-cylinder engines.
Question 7: What is the correct procedure when checking engine oil level?
- Check immediately after turning off a hot engine with the car on a slope
- Check with the engine running and the car level
- Check with the engine off, car on level ground, after letting oil settle (Correct answer)
- Check only when the oil warning light comes on
Correct answer: Check with the engine off, car on level ground, after letting oil settle
Oil level should be checked with the engine off on level ground, allowing time for oil to drain back into the pan so the dipstick reads accurately.
ASVAB Auto and Shop: Engine Systems and Repair 5
What is the purpose of the exhaust gas recirculation (EGR) system?