Engine Performance Practice Exam Test.
Blue smoke is coming from the exhaust pipe of a vehicle. Tech A says that worn piston rings could be the cause. Tech B says that a bad head gasket could be the cause. Who is right?
A. Tech A
B. Tech B
C. Both
D. Neither - CORRECT ANSWER A. Blue smoke...
Blue smoke is coming from the exhaust pipe of a vehicle. Tech A says that worn piston rings could be the
cause. Tech B says that a bad head gasket could be the cause. Who is right?
A. Tech A
B. Tech B
C. Both
D. Neither - CORRECT ANSWER A. Blue smoke means the engine is burning oil, which could be caused by
worn piston rings. Technician B is wrong because a bad head gasket would cause coolant to leak into
one or more cylinders, resulting in white exhaust smoke.
A vacuum gauge is connected to the intake manifold engine and the engine is run at 2,000 rpm. During
the test, the pointer on the gauge fluctuates rapidly between readings of 10 and 22 inches of vacuum.
These test results point to:
A. a leaking intake manifold gasket
B. worn piston rings
C. worn valve guides
D. a weak or broken valve spring - CORRECT ANSWER D. A leaking intake manifold gasket or worn piston
rings would not cause a vacuum gauge needle to fluctuate. Worn valve guides would make the needle
fluctuate at idle but the needle would
steady when engine speed is increased. A weak or broken valve spring will cause a vacuum gauge to
fluctuate or jump from low to high readings.
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 - CORRECT ANSWER B. Advanced ignition timing will cause knock, but
retarded timing will not.
,Tech A says that spark advance on an engine can be tested by listening to the way the engine sounds at
higher rpm. Tech B says that spark advance on an engine can be tested with a timing light that
incorporates an ignition advance meter. Who is right?
A. Tech A
B. Tech B
C. Both
D. Neither - CORRECT ANSWER B. To accurately measure spark advance, use a timing light that
incorporates an
ignition advance meter. The spark advance cannot be determined by listening to the way the engine
sounds.
A regular customer presents his vehicle for service. He describes symptoms of poor drivability and says
that the vehicle has been repaired for the same problem in the past. Which, of the following, should you
do first?
A. connect the vehicle to an engine analyzer
B. check for diagnostic trouble codes
C. check the vehicle service history and check for TSBs, service campaigns and recalls
D. perform a cylinder balance test - CORRECT ANSWER C. Checking the vehicle service history may get
you pointed in the right direction before you even raise the hood. What repairs have been performed
and what parts were installed? What fixed the car before? If it is a recurring problem, maybe a different
course of action is in order. If the vehicle really has failed in the same way, checking TSBs may provide
information on updated parts that weren't available previously and may solve the problem now. When
checking for service campaigns and recalls, you may find that the problem is a defect that the
manufacturer will repair.
Two techs are listening to a tapping noise coming from the top end of a V8 engine. Tech A says the noise
could be a valve needing adjustment. Tech B says the noise could be an exhaust leak. Who is right?
A. Tech A
B. Tech B
C. Both
D. Neither - CORRECT ANSWER C. A tapping noise that does not dissipate after the engine warms up
could be caused by worn valvetrain components or excessive valvetrain clearance. A similar type noise
can sometimes be caused by an exhaust leak at the exhaust manifold/cylinder head juncture.
, Tech A says a high spike line on an oscilloscope indicates disconnected or open plug wire. Tech B says a
high spike line indicates a closed gap on a spark plug. Who is right?
A. Tech A
B. Tech B
C. Both
D. Neither - CORRECT ANSWER A. A higher-by-comparison spike line on an oscilloscope could indicate a
disconnected or open spark plug wire. If a spark plug gap were closed, the oscilloscope would indicate a
very low spike line.
A vehicle can be started with great difficulty, but lacks power, and will not idle. Tech A says that there
could be a hole or tear in the duct between the mass air flow sensor and the throttle body. Tech B says
that a restricted fuel filter is the problem. Who is right?
A. Tech A
B. Tech B
C. Both
D. Neither - CORRECT ANSWER A. The fuel filter may be in need of service, but it is not the cause of the
problem. Unmetered air entering the engine means that there is more air than the amount for which
the engine is delivering fuel. A careful examination of the duct between the air flow sensor and the
throttle body should reveal where the unmetered air is entering.
A vehicle is towed in the with a 'cranks but won't start' condition. A 'noid' light test finds no injector
pulses, and Tech A says the vehicle need a computer. Tech B finds no spark and says the the vehicle
needs an ignition module. Who is right?
A. Tech A
B. Tech B
C. Both
D. Neither - CORRECT ANSWER D. Although the vehicle may need one of these items before being
returned to service, both technicians are jumping to conclusions. A defective crank sensor can
cause both of these symptoms, and that is far more likely than either of the other possibilities. The
correct action is to test until the defective component is located.
Tech A says that evidence of cylinder wear can be found using a cylinder leakage tester. Tech B says that
a blown head gasket can be found using a cylinder leakage tester. Who is right?
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