ASE Master Automobile Technician
Certification Practice Exam 100
Questions And Correct Answers
(Verified Answers) Plus Rationales
2026 Q&A Instant Download Pdf
1. An engine has low compression on one cylinder. Which test best helps
locate whether the loss is past the rings, valves, or head gasket?
A. Vacuum test
B. Cylinder balance test
C. Compression test
D. Cylinder leak-down test
D. Cylinder leak-down test
Leak-down testing pinpoints where pressure is escaping by introducing
compressed air into the cylinder and listening for air at the intake, exhaust, or
crankcase. A compression test only shows that pressure is low, not where it is
going.
2. A vehicle exhibits low oil pressure at idle but normal pressure at higher
RPMs. The most likely cause is:
A. Clogged oil filter
B. Worn engine bearings
C. Faulty oil pressure sensor
D. Thick engine oil
B. Worn engine bearings
Worn bearings increase clearance, lowering oil pressure especially at idle
when oil flow is minimal. At higher RPMs, the pump can keep up with the
increased clearance.
, 3. A technician hears a deep knocking sound that increases with engine
load. What is the probable cause?
A. Piston slap
B. Connecting rod bearing wear
C. Valve train noise
D. Detonation
B. Connecting rod bearing wear
A deep knock under load typically indicates rod bearing wear or clearance
issues. Piston slap is a lighter rattle that is worse when cold. Valve train noise
is a top-end tick. Detonation is a sharp ping.
4. Excessive blue smoke from the exhaust indicates:
A. Coolant burning
B. Oil burning
C. Rich air-fuel mixture
D. Incomplete combustion
B. Oil burning
Blue smoke is a signature sign of oil entering the combustion chamber, often
from worn valve guides or piston rings. Coolant burning produces white
smoke. A rich mixture produces black smoke.
5. A compression test shows one cylinder significantly lower than others.
Adding oil increases pressure. The cause is likely:
A. Leaking valves
B. Worn piston rings
C. Head gasket leak
D. Cracked cylinder head
B. Worn piston rings
Oil seals worn rings temporarily, boosting compression. If the pressure does
not increase, the loss is likely through valves or a head gasket.
6. A vehicle emits white-colored exhaust from its tailpipe at all engine
speeds. Which of these could be the cause?
A. Worn piston rings
, B. A leaking head gasket
C. Worn valve seals
D. A leaking fuel injector
B. A leaking head gasket
A leaking head gasket allows coolant to enter the cylinder, producing white-
gray exhaust. Worn piston rings cause blue/gray exhaust. Leaking valve seals
cause oil consumption. A leaking injector causes black sooty exhaust.
7. Technician A says that main bearing oil clearance can be checked with
plastigage. Technician B says that main bearing oil clearance can be
checked with a dial bore gauge. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
C. Both A and B
Either method can be used to check main bearing oil clearance. Plastigage is
a crush gauge that measures clearance directly. A dial bore gauge measures
the bore and the journal, and the difference is the clearance.
8. Which of the following is NOT a method of correcting excessive valve
stem-to-guide clearance?
A. Knurling the valve stem
B. Knurling the guide
C. Reaming for oversize
D. Guide replacement
A. Knurling the valve stem
The valve stem is hardened and cannot be knurled. Knurling the guide,
reaming for oversize valves, or replacing the guide are all acceptable repair
methods.
9. A vacuum gauge is connected to the intake manifold of an engine
running at idle. The pointer on the gauge fluctuates rapidly but steadies
as the engine speed is increased. The test results indicate:
, A. A leaking intake manifold gasket
B. Worn valve guides
C. Late ignition timing
D. A weak valve spring
B. Worn valve guides
Worn valve guides can cause the needle to fluctuate rapidly at idle but steady
as engine speed increases. A leaking intake manifold gasket or late ignition
timing causes a steady low reading. A weak valve spring causes fluctuation as
engine speed increases.
10.A technician takes a compression reading on a 4-cylinder engine and gets
readings of 140, 135, 135, and 40 psi. Then he performs a wet
compression test, and the readings are almost the same as those in the
first test. Technician A says that a burned valve could cause these
readings. Technician B says that a broken piston ring could cause these
readings. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
A. Technician A only
A burned valve will not allow the cylinder to build compression, and wet and
dry compression tests will be the same. If piston rings were at fault, wet test
readings would exceed dry test results.
11.Technician A says that retarded valve timing can cause high cylinder
compression readings. Technician B says that a lean air/fuel mixture can
cause a high intake manifold vacuum reading. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
D. Neither A or B
Certification Practice Exam 100
Questions And Correct Answers
(Verified Answers) Plus Rationales
2026 Q&A Instant Download Pdf
1. An engine has low compression on one cylinder. Which test best helps
locate whether the loss is past the rings, valves, or head gasket?
A. Vacuum test
B. Cylinder balance test
C. Compression test
D. Cylinder leak-down test
D. Cylinder leak-down test
Leak-down testing pinpoints where pressure is escaping by introducing
compressed air into the cylinder and listening for air at the intake, exhaust, or
crankcase. A compression test only shows that pressure is low, not where it is
going.
2. A vehicle exhibits low oil pressure at idle but normal pressure at higher
RPMs. The most likely cause is:
A. Clogged oil filter
B. Worn engine bearings
C. Faulty oil pressure sensor
D. Thick engine oil
B. Worn engine bearings
Worn bearings increase clearance, lowering oil pressure especially at idle
when oil flow is minimal. At higher RPMs, the pump can keep up with the
increased clearance.
, 3. A technician hears a deep knocking sound that increases with engine
load. What is the probable cause?
A. Piston slap
B. Connecting rod bearing wear
C. Valve train noise
D. Detonation
B. Connecting rod bearing wear
A deep knock under load typically indicates rod bearing wear or clearance
issues. Piston slap is a lighter rattle that is worse when cold. Valve train noise
is a top-end tick. Detonation is a sharp ping.
4. Excessive blue smoke from the exhaust indicates:
A. Coolant burning
B. Oil burning
C. Rich air-fuel mixture
D. Incomplete combustion
B. Oil burning
Blue smoke is a signature sign of oil entering the combustion chamber, often
from worn valve guides or piston rings. Coolant burning produces white
smoke. A rich mixture produces black smoke.
5. A compression test shows one cylinder significantly lower than others.
Adding oil increases pressure. The cause is likely:
A. Leaking valves
B. Worn piston rings
C. Head gasket leak
D. Cracked cylinder head
B. Worn piston rings
Oil seals worn rings temporarily, boosting compression. If the pressure does
not increase, the loss is likely through valves or a head gasket.
6. A vehicle emits white-colored exhaust from its tailpipe at all engine
speeds. Which of these could be the cause?
A. Worn piston rings
, B. A leaking head gasket
C. Worn valve seals
D. A leaking fuel injector
B. A leaking head gasket
A leaking head gasket allows coolant to enter the cylinder, producing white-
gray exhaust. Worn piston rings cause blue/gray exhaust. Leaking valve seals
cause oil consumption. A leaking injector causes black sooty exhaust.
7. Technician A says that main bearing oil clearance can be checked with
plastigage. Technician B says that main bearing oil clearance can be
checked with a dial bore gauge. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
C. Both A and B
Either method can be used to check main bearing oil clearance. Plastigage is
a crush gauge that measures clearance directly. A dial bore gauge measures
the bore and the journal, and the difference is the clearance.
8. Which of the following is NOT a method of correcting excessive valve
stem-to-guide clearance?
A. Knurling the valve stem
B. Knurling the guide
C. Reaming for oversize
D. Guide replacement
A. Knurling the valve stem
The valve stem is hardened and cannot be knurled. Knurling the guide,
reaming for oversize valves, or replacing the guide are all acceptable repair
methods.
9. A vacuum gauge is connected to the intake manifold of an engine
running at idle. The pointer on the gauge fluctuates rapidly but steadies
as the engine speed is increased. The test results indicate:
, A. A leaking intake manifold gasket
B. Worn valve guides
C. Late ignition timing
D. A weak valve spring
B. Worn valve guides
Worn valve guides can cause the needle to fluctuate rapidly at idle but steady
as engine speed increases. A leaking intake manifold gasket or late ignition
timing causes a steady low reading. A weak valve spring causes fluctuation as
engine speed increases.
10.A technician takes a compression reading on a 4-cylinder engine and gets
readings of 140, 135, 135, and 40 psi. Then he performs a wet
compression test, and the readings are almost the same as those in the
first test. Technician A says that a burned valve could cause these
readings. Technician B says that a broken piston ring could cause these
readings. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
A. Technician A only
A burned valve will not allow the cylinder to build compression, and wet and
dry compression tests will be the same. If piston rings were at fault, wet test
readings would exceed dry test results.
11.Technician A says that retarded valve timing can cause high cylinder
compression readings. Technician B says that a lean air/fuel mixture can
cause a high intake manifold vacuum reading. Who is right?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
D. Neither A or B
