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ASE A8 Engine Performance Exam | Latest Verified
Questions and Detailed Answers
OVERVIEW DESCRIPTION
This Comprehensive set of multiple choice questions is designed for the ASE A8
Engine Performance exam, which assesses a technician’s ability to diagnose and
repair complex engine systems. The content is organized according to the official ASE
task list, covering six core areas: General Engine Diagnosis; Computerized Engine
Controls; Ignition System Diagnosis and Repair; Fuel, Air Induction, and Exhaust
Systems; Emissions Control Systems; and Engine Electrical Systems. Each question
reflects practical, real-world troubleshooting scenarios that evaluate a candidate’s
skill in interpreting scan tool data, analyzing sensor waveforms, and pinpointing faults
in fuel, ignition, emissions, and electronic control systems. The exam is administered
by the National Institute for Automotive Service Excellence (ASE).
A. General Engine Diagnosis
QUESTION 1
A vehicle has a rough idle and the owner complains of poor fuel economy. A vacuum
gauge connected to the intake manifold shows a steady reading of 10 in. Hg (normal is
17–21 in. Hg). Which of the following is the MOST likely cause?
A. Worn piston rings
B. Leaking intake manifold gasket
C. Stuck-open EGR valve
D. Retarded ignition timing
CORRECT ANSWER: D
EXPERT RATIONALE: A steady low vacuum reading typically indicates retarded ignition
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timing or a large vacuum leak. The other options cause different vacuum patterns (e.g.,
floating needle for rings, intermittent drop for stuck EGR).
QUESTION 2
An engine produces a sharp metallic rapping noise that becomes louder under load and
increases with engine speed. The noise is most likely coming from:
A. Worn connecting rod bearings
B. Piston slap
C. Excessive main bearing clearance
D. Collapsed lifter
CORRECT ANSWER: A
EXPERT RATIONALE: A sharp, heavy rapping noise that worsens under load is classic
for rod bearing wear. Main bearing noise is a heavier thump, piston slap is a hollow
knock cold, and a lifter tick is higher-pitched.
QUESTION 3
Technician A says that a cylinder compression test should be performed with the engine
warm and the throttle plate closed. Technician B says that a cylinder leak-down test can
identify the source of compression loss. Who is correct?
A. Technician A only
B. Technician B only
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C. Both A and B
D. Neither A nor B
CORRECT ANSWER: B
EXPERT RATIONALE: Compression tests are performed with the throttle wide open
(WOT) to allow maximum airflow. A leak-down test uses compressed air to pinpoint
where pressure escapes (intake, exhaust, crankcase).
QUESTION 4
A power balance test reveals that cylinder #3 has no drop in RPM when its fuel injector
is disabled. All of the following could be the cause EXCEPT:
A. Fouled spark plug on #3
B. Burned exhaust valve on #3
C. A restricted fuel injector on #3
D. A worn camshaft lobe on cylinder #2
CORRECT ANSWER: D
EXPERT RATIONALE: A power balance test identifies a weak cylinder by disabling each
cylinder in turn. A fault on a different cylinder (#2) would not cause #3 to show no RPM
drop.
QUESTION 5
A cylinder leak-down test shows 30% leakage on cylinder #4. Air can be heard escaping
from the oil fill cap. Which component is most likely at fault?
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A. Intake valve
B. Exhaust valve
C. Piston rings
D. Head gasket
CORRECT ANSWER: C
EXPERT RATIONALE: Air escaping into the crankcase (heard through the oil fill)
indicates leakage past the piston rings. Intake/exhaust valve leakage would be heard at
the throttle body or tailpipe.
QUESTION 6
During a vacuum test, the gauge needle fluctuates rapidly between 15 and 20 in. Hg at
idle. This condition is most likely caused by:
A. A leaking intake manifold gasket
B. A stuck-open EGR valve
C. Worn valve guides or valve sticking
D. Late ignition timing
CORRECT ANSWER: C
EXPERT RATIONALE: Rapid fluctuation of the vacuum needle at idle points to sticking
valves or worn guides. A steady low reading suggests a leak or timing issue, while
intermittent drops suggest EGR or valve problems.
ASE A8 Engine Performance Exam | Latest Verified
Questions and Detailed Answers
OVERVIEW DESCRIPTION
This Comprehensive set of multiple choice questions is designed for the ASE A8
Engine Performance exam, which assesses a technician’s ability to diagnose and
repair complex engine systems. The content is organized according to the official ASE
task list, covering six core areas: General Engine Diagnosis; Computerized Engine
Controls; Ignition System Diagnosis and Repair; Fuel, Air Induction, and Exhaust
Systems; Emissions Control Systems; and Engine Electrical Systems. Each question
reflects practical, real-world troubleshooting scenarios that evaluate a candidate’s
skill in interpreting scan tool data, analyzing sensor waveforms, and pinpointing faults
in fuel, ignition, emissions, and electronic control systems. The exam is administered
by the National Institute for Automotive Service Excellence (ASE).
A. General Engine Diagnosis
QUESTION 1
A vehicle has a rough idle and the owner complains of poor fuel economy. A vacuum
gauge connected to the intake manifold shows a steady reading of 10 in. Hg (normal is
17–21 in. Hg). Which of the following is the MOST likely cause?
A. Worn piston rings
B. Leaking intake manifold gasket
C. Stuck-open EGR valve
D. Retarded ignition timing
CORRECT ANSWER: D
EXPERT RATIONALE: A steady low vacuum reading typically indicates retarded ignition
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timing or a large vacuum leak. The other options cause different vacuum patterns (e.g.,
floating needle for rings, intermittent drop for stuck EGR).
QUESTION 2
An engine produces a sharp metallic rapping noise that becomes louder under load and
increases with engine speed. The noise is most likely coming from:
A. Worn connecting rod bearings
B. Piston slap
C. Excessive main bearing clearance
D. Collapsed lifter
CORRECT ANSWER: A
EXPERT RATIONALE: A sharp, heavy rapping noise that worsens under load is classic
for rod bearing wear. Main bearing noise is a heavier thump, piston slap is a hollow
knock cold, and a lifter tick is higher-pitched.
QUESTION 3
Technician A says that a cylinder compression test should be performed with the engine
warm and the throttle plate closed. Technician B says that a cylinder leak-down test can
identify the source of compression loss. Who is correct?
A. Technician A only
B. Technician B only
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C. Both A and B
D. Neither A nor B
CORRECT ANSWER: B
EXPERT RATIONALE: Compression tests are performed with the throttle wide open
(WOT) to allow maximum airflow. A leak-down test uses compressed air to pinpoint
where pressure escapes (intake, exhaust, crankcase).
QUESTION 4
A power balance test reveals that cylinder #3 has no drop in RPM when its fuel injector
is disabled. All of the following could be the cause EXCEPT:
A. Fouled spark plug on #3
B. Burned exhaust valve on #3
C. A restricted fuel injector on #3
D. A worn camshaft lobe on cylinder #2
CORRECT ANSWER: D
EXPERT RATIONALE: A power balance test identifies a weak cylinder by disabling each
cylinder in turn. A fault on a different cylinder (#2) would not cause #3 to show no RPM
drop.
QUESTION 5
A cylinder leak-down test shows 30% leakage on cylinder #4. Air can be heard escaping
from the oil fill cap. Which component is most likely at fault?
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A. Intake valve
B. Exhaust valve
C. Piston rings
D. Head gasket
CORRECT ANSWER: C
EXPERT RATIONALE: Air escaping into the crankcase (heard through the oil fill)
indicates leakage past the piston rings. Intake/exhaust valve leakage would be heard at
the throttle body or tailpipe.
QUESTION 6
During a vacuum test, the gauge needle fluctuates rapidly between 15 and 20 in. Hg at
idle. This condition is most likely caused by:
A. A leaking intake manifold gasket
B. A stuck-open EGR valve
C. Worn valve guides or valve sticking
D. Late ignition timing
CORRECT ANSWER: C
EXPERT RATIONALE: Rapid fluctuation of the vacuum needle at idle points to sticking
valves or worn guides. A steady low reading suggests a leak or timing issue, while
intermittent drops suggest EGR or valve problems.
