ASE A8 Engine Performance Practice
Exam 100 Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A Instant
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1. A customer complains that the vehicle has a momentary hesitation only
during acceleration. Which of the following is the MOST likely cause?
A) A faulty exhaust gas recirculation (EGR) valve
B) A faulty oxygen sensor (O2)
C) A faulty positive crankcase ventilation (PCV) valve
D) A faulty throttle position sensor (TP)
A faulty TP sensor can cause a dead spot or an incorrect voltage signal during
throttle opening, leading to a momentary hesitation during acceleration. The
ECM does not receive the correct input to adjust the fuel mixture properly for
the sudden increase in airflow.
2. An engine has a code indicating insufficient EGR flow, and the EGR solenoid
has been diagnosed as faulty. This condition will MOST likely result in:
A) High CO emissions
B) High HC emissions
C) High CO2 emissions
D) High NOx emissions
,NOx is formed at high cylinder temperatures during combustion. The EGR
system reduces these temperatures by introducing inert exhaust gases into
the intake charge. A stuck-closed or insufficient EGR valve will not provide this
cooling effect, leading to elevated combustion temperatures and high NOx
emissions.
3. Two technicians are discussing variable valve timing (VVT) systems.
Technician A says a faulty oil control valve could be the cause of a sudden
drop in fuel economy. Technician B says contaminated engine oil can also
cause this condition. Who is correct?
A) Technician A only
B) Technician B only
C) Both Technician A and Technician B
D) Neither Technician A nor Technician B
VVT systems adjust valve timing to optimize engine performance and fuel
economy. The actuators and phasers are operated by oil pressure, making
them sensitive to oil quality and flow. A faulty oil control valve can prevent
proper VVT operation, and contaminated oil can clog the system, both
leading to a loss of fuel economy.
4. A cylinder compression test is performed, and two adjacent cylinders show
low compression. What is the MOST likely cause of these test results?
A) Burned exhaust valves
B) Weak piston rings
C) A faulty head gasket
D) Incorrect valve timing
When two adjacent cylinders show low compression, it is often due to a head
gasket failure that allows compression to leak between the two cylinders. A
,burned exhaust valve or weak piston rings typically affect only one cylinder.
Incorrect valve timing would generally affect all cylinders.
5. A vehicle has a vacuum gauge connected to an intake manifold port. The
needle fluctuates between 15 "Hg and 20 "Hg at idle. This reading MOST
likely indicates:
A) A normal condition
B) Late ignition or valve timing
C) A burned exhaust valve or engine misfire
D) A restricted exhaust
A normal, steady vacuum reading at idle typically ranges from 17–21 "Hg. A
fluctuating needle between 15 and 20 "Hg indicates an intermittent loss of
vacuum, which is a classic symptom of a stuck valve or an engine misfire. A
restricted exhaust would cause a slow drop at idle.
6. After performing a wet compression test (adding oil to the cylinder), the
pressure in each cylinder increases. What does this indicate?
A) Burned valve
B) Worn piston rings
C) Faulty head gasket
D) Incorrect valve timing
If compression increases after adding oil, the oil has improved the seal
between the piston rings and the cylinder wall. A burned valve would show
no change because the oil cannot seal a valve leak.
7. Blue smoke is coming from the exhaust pipe of a vehicle. What most likely
is the cause?
A) Worn piston ring
, B) Bad head gasket
C) Leaking fuel injector
D) Vacuum leak
Blue smoke indicates oil is entering the combustion chamber. Worn piston
rings allow oil to pass into the cylinder, producing blue-gray exhaust. A bad
head gasket produces white smoke, and a leaking fuel injector produces black
smoke.
8. A vacuum gauge is connected to the intake manifold of an engine and the
engine is run at 2000 rpm. During the test, the pointer on the gauge
fluctuates rapidly between readings of 10 and 20 inches of vacuum. These
test results point to:
A) A leaking intake manifold
B) Worn piston rings
C) Worn valve guides
D) A weak or broken valve spring
A weak or broken valve spring causes the vacuum gauge to fluctuate or jump
from high to low readings as the valve fails to seal consistently at higher
RPMs.
9. Engine detonation (knock) could be caused by any of the following EXCEPT:
A) A lean air/fuel mixture
B) Retarded ignition timing
C) Excess carbon in the combustion chambers
D) A stuck-closed EGR valve
Advanced ignition timing will cause knock, but retarded timing will not. A
lean mixture, excess carbon (which increases compression), and a stuck-
closed EGR valve all raise combustion temperatures and promote detonation.
Exam 100 Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A Instant
Download Pdf
1. A customer complains that the vehicle has a momentary hesitation only
during acceleration. Which of the following is the MOST likely cause?
A) A faulty exhaust gas recirculation (EGR) valve
B) A faulty oxygen sensor (O2)
C) A faulty positive crankcase ventilation (PCV) valve
D) A faulty throttle position sensor (TP)
A faulty TP sensor can cause a dead spot or an incorrect voltage signal during
throttle opening, leading to a momentary hesitation during acceleration. The
ECM does not receive the correct input to adjust the fuel mixture properly for
the sudden increase in airflow.
2. An engine has a code indicating insufficient EGR flow, and the EGR solenoid
has been diagnosed as faulty. This condition will MOST likely result in:
A) High CO emissions
B) High HC emissions
C) High CO2 emissions
D) High NOx emissions
,NOx is formed at high cylinder temperatures during combustion. The EGR
system reduces these temperatures by introducing inert exhaust gases into
the intake charge. A stuck-closed or insufficient EGR valve will not provide this
cooling effect, leading to elevated combustion temperatures and high NOx
emissions.
3. Two technicians are discussing variable valve timing (VVT) systems.
Technician A says a faulty oil control valve could be the cause of a sudden
drop in fuel economy. Technician B says contaminated engine oil can also
cause this condition. Who is correct?
A) Technician A only
B) Technician B only
C) Both Technician A and Technician B
D) Neither Technician A nor Technician B
VVT systems adjust valve timing to optimize engine performance and fuel
economy. The actuators and phasers are operated by oil pressure, making
them sensitive to oil quality and flow. A faulty oil control valve can prevent
proper VVT operation, and contaminated oil can clog the system, both
leading to a loss of fuel economy.
4. A cylinder compression test is performed, and two adjacent cylinders show
low compression. What is the MOST likely cause of these test results?
A) Burned exhaust valves
B) Weak piston rings
C) A faulty head gasket
D) Incorrect valve timing
When two adjacent cylinders show low compression, it is often due to a head
gasket failure that allows compression to leak between the two cylinders. A
,burned exhaust valve or weak piston rings typically affect only one cylinder.
Incorrect valve timing would generally affect all cylinders.
5. A vehicle has a vacuum gauge connected to an intake manifold port. The
needle fluctuates between 15 "Hg and 20 "Hg at idle. This reading MOST
likely indicates:
A) A normal condition
B) Late ignition or valve timing
C) A burned exhaust valve or engine misfire
D) A restricted exhaust
A normal, steady vacuum reading at idle typically ranges from 17–21 "Hg. A
fluctuating needle between 15 and 20 "Hg indicates an intermittent loss of
vacuum, which is a classic symptom of a stuck valve or an engine misfire. A
restricted exhaust would cause a slow drop at idle.
6. After performing a wet compression test (adding oil to the cylinder), the
pressure in each cylinder increases. What does this indicate?
A) Burned valve
B) Worn piston rings
C) Faulty head gasket
D) Incorrect valve timing
If compression increases after adding oil, the oil has improved the seal
between the piston rings and the cylinder wall. A burned valve would show
no change because the oil cannot seal a valve leak.
7. Blue smoke is coming from the exhaust pipe of a vehicle. What most likely
is the cause?
A) Worn piston ring
, B) Bad head gasket
C) Leaking fuel injector
D) Vacuum leak
Blue smoke indicates oil is entering the combustion chamber. Worn piston
rings allow oil to pass into the cylinder, producing blue-gray exhaust. A bad
head gasket produces white smoke, and a leaking fuel injector produces black
smoke.
8. A vacuum gauge is connected to the intake manifold of an engine and the
engine is run at 2000 rpm. During the test, the pointer on the gauge
fluctuates rapidly between readings of 10 and 20 inches of vacuum. These
test results point to:
A) A leaking intake manifold
B) Worn piston rings
C) Worn valve guides
D) A weak or broken valve spring
A weak or broken valve spring causes the vacuum gauge to fluctuate or jump
from high to low readings as the valve fails to seal consistently at higher
RPMs.
9. Engine detonation (knock) could be caused by any of the following EXCEPT:
A) A lean air/fuel mixture
B) Retarded ignition timing
C) Excess carbon in the combustion chambers
D) A stuck-closed EGR valve
Advanced ignition timing will cause knock, but retarded timing will not. A
lean mixture, excess carbon (which increases compression), and a stuck-
closed EGR valve all raise combustion temperatures and promote detonation.
