ASE Medium Heavy Truck T1 Gasoline
Engines Practice Exam 100 Questions
And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A
Instant Download Pdf
1. A gasoline engine is hard to start in cold weather. Which of the following is
the LEAST likely cause?
A) Incorrect spark plug gap
B) Weak battery
C) Excessive fuel injection pressure
D) Dirty air filter
Rationale: Cold-start issues are typically caused by inadequate voltage (weak
battery), poor ignition (wrong spark plug gap), or restricted airflow (dirty
filter). Excessive fuel injection pressure would actually help vaporize fuel in
cold conditions; insufficient pressure would be the problem.
2. When performing a compression test on a gasoline engine, what is the
normal compression ratio specification for a medium-duty truck engine?
A) 6:1 to 8:1
B) 8:1 to 10:1
C) 10:1 to 12:1
D) 12:1 to 14:1
Rationale: Most gasoline engines used in medium-duty trucks operate with
compression ratios between 8:1 and 10:1. Lower ratios are found in older
engines, while higher ratios are typically reserved for high-performance
applications.
,3. A technician is diagnosing a gasoline engine with excessive oil
consumption. Which of the following is the MOST common cause?
A) Excessive ring gap
B) Worn valve stem seals
C) Incorrect oil viscosity
D) Overfilled oil level
Rationale: Worn valve stem seals allow oil to be drawn into the combustion
chamber during the intake stroke, causing blue smoke and excessive oil
consumption. Incorrect viscosity would result in external leaks, not
consumption.
4. Which fuel system component is responsible for maintaining constant fuel
pressure regardless of engine speed?
A) Fuel pump
B) Fuel injector
C) Fuel pressure regulator
D) Fuel filter
Rationale: The fuel pressure regulator maintains a constant pressure
differential across the fuel injectors by routing excess fuel back to the tank via
the return line.
5. A gasoline engine is running rough at idle. A cylinder balance test finds that
cylinder 3 is significantly lower than the others. What is the MOST likely
cause?
A) Incorrect valve timing
B) Fouled spark plug
C) Leaking fuel injector
D) Disconnected spark plug wire
Rationale: A single low cylinder on a balance test typically points to an
ignition or fuel delivery issue specific to that cylinder. A fouled spark plug is a
common cause.
6. A medium-duty truck with a large-displacement gasoline engine has a
rough idle and low power. A cylinder compression test shows one cylinder
reading 90 psi while the others read about 155 psi. Which is the MOST likely
, cause?
A) A leaking head gasket, burned valve, or worn rings in that cylinder
B) A restricted exhaust system affecting all cylinders equally
C) A weak battery causing slow cranking
D) A clogged fuel injector on that cylinder
Rationale: A single low-compression cylinder points to a mechanical sealing
problem unique to that cylinder, such as a burned valve, blown head gasket,
or worn piston rings.
7. Technician A says a cylinder leakage (leak-down) test pinpoints where
compression is escaping. Technician B says air heard at the throttle body
during a leak-down test indicates a leaking intake valve. Who is correct?
A) Neither A nor B
B) Both A and B
C) A only
D) B only
Rationale: A leak-down test applies regulated air to a cylinder at TDC and lets
you listen for where it escapes. Air at the intake indicates a leaking intake
valve, at the exhaust indicates an exhaust valve, and into the crankcase
indicates rings.
8. During a running compression test, the snap-throttle reading is much lower
than the cranking compression reading on the same cylinder. This MOST likely
indicates:
A) A stuck-open thermostat
B) Excessive ignition timing advance
C) A restricted intake (such as a clogged air filter)
D) Worn piston rings only
Rationale: An abnormally low snap-throttle reading compared to cranking
points to an intake restriction limiting cylinder filling, reducing volumetric
efficiency.
9. What is the primary function of the camshaft in a gasoline engine?
A) Increase fuel efficiency
B) Control the opening and closing of valves
Engines Practice Exam 100 Questions
And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A
Instant Download Pdf
1. A gasoline engine is hard to start in cold weather. Which of the following is
the LEAST likely cause?
A) Incorrect spark plug gap
B) Weak battery
C) Excessive fuel injection pressure
D) Dirty air filter
Rationale: Cold-start issues are typically caused by inadequate voltage (weak
battery), poor ignition (wrong spark plug gap), or restricted airflow (dirty
filter). Excessive fuel injection pressure would actually help vaporize fuel in
cold conditions; insufficient pressure would be the problem.
2. When performing a compression test on a gasoline engine, what is the
normal compression ratio specification for a medium-duty truck engine?
A) 6:1 to 8:1
B) 8:1 to 10:1
C) 10:1 to 12:1
D) 12:1 to 14:1
Rationale: Most gasoline engines used in medium-duty trucks operate with
compression ratios between 8:1 and 10:1. Lower ratios are found in older
engines, while higher ratios are typically reserved for high-performance
applications.
,3. A technician is diagnosing a gasoline engine with excessive oil
consumption. Which of the following is the MOST common cause?
A) Excessive ring gap
B) Worn valve stem seals
C) Incorrect oil viscosity
D) Overfilled oil level
Rationale: Worn valve stem seals allow oil to be drawn into the combustion
chamber during the intake stroke, causing blue smoke and excessive oil
consumption. Incorrect viscosity would result in external leaks, not
consumption.
4. Which fuel system component is responsible for maintaining constant fuel
pressure regardless of engine speed?
A) Fuel pump
B) Fuel injector
C) Fuel pressure regulator
D) Fuel filter
Rationale: The fuel pressure regulator maintains a constant pressure
differential across the fuel injectors by routing excess fuel back to the tank via
the return line.
5. A gasoline engine is running rough at idle. A cylinder balance test finds that
cylinder 3 is significantly lower than the others. What is the MOST likely
cause?
A) Incorrect valve timing
B) Fouled spark plug
C) Leaking fuel injector
D) Disconnected spark plug wire
Rationale: A single low cylinder on a balance test typically points to an
ignition or fuel delivery issue specific to that cylinder. A fouled spark plug is a
common cause.
6. A medium-duty truck with a large-displacement gasoline engine has a
rough idle and low power. A cylinder compression test shows one cylinder
reading 90 psi while the others read about 155 psi. Which is the MOST likely
, cause?
A) A leaking head gasket, burned valve, or worn rings in that cylinder
B) A restricted exhaust system affecting all cylinders equally
C) A weak battery causing slow cranking
D) A clogged fuel injector on that cylinder
Rationale: A single low-compression cylinder points to a mechanical sealing
problem unique to that cylinder, such as a burned valve, blown head gasket,
or worn piston rings.
7. Technician A says a cylinder leakage (leak-down) test pinpoints where
compression is escaping. Technician B says air heard at the throttle body
during a leak-down test indicates a leaking intake valve. Who is correct?
A) Neither A nor B
B) Both A and B
C) A only
D) B only
Rationale: A leak-down test applies regulated air to a cylinder at TDC and lets
you listen for where it escapes. Air at the intake indicates a leaking intake
valve, at the exhaust indicates an exhaust valve, and into the crankcase
indicates rings.
8. During a running compression test, the snap-throttle reading is much lower
than the cranking compression reading on the same cylinder. This MOST likely
indicates:
A) A stuck-open thermostat
B) Excessive ignition timing advance
C) A restricted intake (such as a clogged air filter)
D) Worn piston rings only
Rationale: An abnormally low snap-throttle reading compared to cranking
points to an intake restriction limiting cylinder filling, reducing volumetric
efficiency.
9. What is the primary function of the camshaft in a gasoline engine?
A) Increase fuel efficiency
B) Control the opening and closing of valves
