1.
A wet compression test is being performed on a four cylinder engine. The number two cylinder is low and the compression reading stays the same after adding oil. Technician A says the engine needs piston rings. Technician B says the engine has a faulty valve. Who is correct?
Correct Answer
B. Technician B
Explanation
Answer A is wrong. It would be the piston rings if the readings would have increased.
Answer B is correct. If there is no change in the compression reading after adding oil to the cylinder, the cylinder has a faulty valve.
Answer C is wrong. Technician B is correct.
Answer D is wrong. Technician B is correct.
2.
An engine is making a knocking sound that changes with RPM, and the noise disappears while a cylinder is being tested during the cylinder balance test. Which of the following could be the cause?
Correct Answer
A. Rod bearing
Explanation
A bad rod bearing will make a knocking sound with changes in RPM and disappear when the cylinder is shorted out.
3.
A power balance test is being performed. Technician A says to note the engine RPM before and during the test for each cylinder. Technician B says to record the RPM drop for each cylinder. Who is right?
Correct Answer
A. Technician A
Explanation
Technician A is correct. During a power balance test, it is important to note the engine RPM before and during the test for each cylinder. This helps in identifying any discrepancies or imbalances in the power output of each cylinder. By comparing the RPM values, technicians can determine if there is a drop in power in any specific cylinder, indicating potential issues such as a misfire or a faulty spark plug. Technician B's suggestion to record the RPM drop is not sufficient on its own, as it does not provide the necessary information to diagnose the specific cylinder causing the issue.
4.
7. A technician installs a radiator pressure tester on the radiator of a cold engine. After starting the engine the pressure quickly rises to 18 psi. Technician A says this is a normal condition. Technician B says the engine has a leaking cylinder head gasket. Who is correct?
Correct Answer
B. Technician B
Explanation
Answer A is wrong. It should take time for the pressure to build.
Answer B is correct. A leaking head gasket will force combustion into the coolant system causing an increase in system pressure.
Answer C is wrong. Technician B is correct.
Answer D is wrong. Technician B is correct.
5.
A vehicle has heavy white smoke emitting from its tailpipe at all engine speeds. The cause of this problem is:
Correct Answer
B. A leaking head gasket
Explanation
Answer A is wrong. Worn piston rings result in blow-by and oil burning in the combustion chamber producing blue/gray smoke.
Answer B is correct. A leaking head gasket results in a coolant leak from the jacket to the cylinder producing white/gray smoke.
Answer C is wrong. Leaking valve seals result in oil entering the combustion chamber, especially overnight or after sitting a while. At start up the engine will produce blue/gray smoke from this oil burning in the combustion chamber. This symptom may go away after the engine runs a while, but return again after the vehicle sits.
Answer D is wrong. A leaking fuel injector results in a rich condition producing excessive hydrocarbons and black smoke.
6.
The engine coolant's specific gravity (freeze point) can be measured by which tool?
Correct Answer
D. Hydrometer
Explanation
There are two main type of antifreeze testers available on the market today. Hydrometers and Refractometers. Hydrometers measure the specific gravity of antifreeze and refractometers measure the speed with which light travels through a sample of antifreeze.
7.
Technician A says a supercharger uses an intercooler to keep the engine's oil cool. Technician B says intercoolers are used on turbochargers to keep the oil cool. Who is correct?
Correct Answer
D. Neither Technician A or B
Explanation
Answer A. is wrong. Superchargers use an intercooler to keep the air charge cool.
Answer B is wrong. Turbochargers also use an intercooler to keep the air charge cool.
Answer C is wrong. Neither technician is correct.
Answer D is correct. Neither technician is correct.
8.
Two technicians are discussing a turbocharged engine. Technician A says the wastegate is a component used to control boost pressure. Technician B says when opened the wastegate diverts exhaust gas from the turbine wheel. Who is correct?
Correct Answer
C. Both Technician A and B
Explanation
Answer A is wrong. The wastegate is controlled by a valve and releases excess pressure back to the exhaust stream. This device is used to control intake manifold pressure.
Answer B is wrong. They are both right. When the gate opens exhaust by-passes the turbine wheel reducing intake manifold pressure.
Answer C is correct. Both technicians are correct.
Answer D is wrong. Both technicians are correct.
9.
During a cylinder leakage test air bubbles appear coming from the radiator neck. Technician A says this may be caused by a leaking intake valve. Technician B says the engine may have a crack in the engine block. Who is correct?
Correct Answer
A. Technician A
Explanation
Answer A is wrong.
Answer B is correct. The blocks deck area and cylinder head will allow compression to leak into the coolant jacket.
Answer C is wrong.
Answer D is wrong.
10.
This question is not like the others. It has the word EXCEPT. For this question, look for the choice that could NOT cause the described situation. Read the entire question carefully before choosing your answer.
All of the following are reasons why you must disable the fuel injection system and ignition system when conducting an engine compression test, EXCEPT:
Correct Answer
D. Prevents inaccurate readings
Explanation
Disabling the fuel injection system and ignition system during an engine compression test is necessary to prevent damage to the ignition system, prevent fuel injection into the cylinders, and prevent an engine fire. However, it does not prevent inaccurate readings. Disabling these systems ensures that the engine is not running and allows for accurate measurement of compression in the cylinders.
11.
An engine has a noise that goes away as the engine warms and reaches operating temperature. Which of these is the most likely cause.
Correct Answer
C. Piston to wall clearance
Explanation
Answer A is wrong. A loose main bolt is not likely to go away as the engine reaches operating temperature.
Answer B is wrong. A spun connecting rod bearing is not likely to go away as the engine reaches operating temperature.
Answer C is correct. As the piston expands the clearance between it and the cylinder wall decreases and so does the noise. Also known as piston slap.
Answer D is wrong. A loose intake manifold will cause low vacuum.
12.
A vehicle vibrates only when placed in reverse. The most likely cause of this condition is:
Correct Answer
D. Faulty engine mount
Explanation
Answer A is wrong. Crossed ignition wires would likely cause a vibration in other speeds and gears as well.
Answer B is wrong. A clogged or faulty fuel injector would likely cause a vibration in other speeds and gears as well.
Answer C is wrong. A faulty or improperly replaced balance shaft would cause a vibration in all gears.
Answer D is correct. A worn or broken engine mount would result in a vibration only in reverse or drive.
13.
A vehicle's cooling system is loosing coolant. There is major corrosion around the aluminum water pump. Which of these are the most likely cause.
Correct Answer
B. Electrolysis
Explanation
Answer A is wrong. A stuck open thermostat will cause a vehicle to take too long to reach operating temperature. May also cause unwanted hot spots.
Answer B is correct. Electrolysis causes corrosion of dissimilar metals in a cooling system. The weaker metal of the two (aluminum) will corrode.
Answer C is wrong. A loose radiator cap will cause an engine to overheat.
Answer D is wrong. A faulty head gasket will result in gases and compression leaking from the compression chamber.
14.
What engine seal is pictured in the illustration to the right?
Correct Answer
D. Valve stem seal
Explanation
The correct answer is valve stem seal. The illustration to the right shows a seal that is typically used to prevent oil from leaking past the valve stems in an engine. This seal is located in the cylinder head and helps to maintain proper lubrication and prevent oil consumption. It is an important component in ensuring the efficient operation of the engine.
15.
The reading on the micrometer indicates:
Correct Answer
D. 6.50mm
Explanation
Answer A is wrong. The micrometers reading is not 6.05 it is 6.50mm.
Answer B is wrong. The micrometers reading is not 6.00 it is 6.50mm.
Answer C is wrong. The micrometers reading is not 5.50 it is 6.50mm.
Answer D is correct. The micrometers reading is 6.50 mm.
16.
During a cylinder leakage test air bubbles appear coming from the radiator neck. Technician A says this may be caused by a leaking intake valve. Technician B says the engine may have a crack in the engine block. Who is correct?
Correct Answer
B. Technician B
Explanation
Answer A is wrong.
Answer B is correct. The blocks deck area and cylinder head will allow compression to leak into the coolant jacket.
Answer C is wrong.
Answer D is wrong.
17.
Technician A says the ridge must be removed before installing new pistons. Technician B says a ridge reamer is used. Who is correct?
Correct Answer
C. Both Technician A and B
Explanation
Answer A is wrong. Both technicians are correct.
Answer B is wrong. Both technicians are correct.
Answer C is correct. The ridge is removed with a ridge reamer before installing the new pistons.
Answer D is wrong. Both technicians are correct.
18.
A cylinder power balance test is being performed on a vehicle with sequential fuel infection. The #5 cylinders RPM drop is less than all of the others. Technician A says this could be due to a restriction in the fuel injector. Technician B says this could be due to leaking secondary insulation. Who is correct?
Correct Answer
C. Both Technician A and B
Explanation
Answer A is wrong. Both technicians are correct.
Answer B is wrong. Both technicians are correct.
Answer C is correct. Both restricted fuel injectors and leaking secondary wires will reduce the cylinders contribution. Anything that would have an effect on the cylinders power. It could be mechanical like a faulty valve, possibly the ignition, or the fuel mixture affecting this cylinders power output.
Answer D is wrong. Both technicians are correct.
19.
A compression test is being performed on a vehicle. The #1 cylinder is 30lbs. lower than specifications. The pressure increases after injecting oil into the cylinder. Technician A says that excessive carbon buildup is the cause of this condition. Technician B says the results of this test indicate one of the cylinders valves are defective. Who is correct?
Correct Answer
D. Neither Technician A or B
Explanation
Answer A is wrong.
Answer B is wrong.
Answer C is wrong.
Answer D is correct. Neither technician is correct. When injecting oil increases the cylinders pressure, the piston rings are faulty. Compression is blowing past this weak seal.
20.
The least likely to cause low oil pressure in an engine is:
Correct Answer
D. Worn valve guides
Explanation
Answer A. is wrong. This is a least question. An open oil pressure valve will cause low oil pressure.
Answer B is wrong. This is a least question. Worn main crankshaft bearings will cause low oil pressure.
Answer C is wrong. This is a least question. Worn camshaft bearings will lower oil pressure.
Answer D is correct. This is the least likely. It is unlikely that a valve guide will lower oil pressure.
21.
The top compression ring groove of piston is worn excessively and the gap is found to be larger than specifications. The technician would most likely:
Correct Answer
D. Replace the piston
Explanation
Answer A is wrong. Many manufacturers install tapered rings on their pistons factory. The compression pressure actually help the ring seal against the cylinder.
Answer B is wrong. Installing a larger piston ring would not repair this condition.
Answer C is wrong. This was done to remove carbon from the ring grooves before measurements were taken.
Answer D is correct. Replacing the piston is the most likely answer.
22.
A technician performs a battery capacity test on a vehicle that will not start. The test results in a reading of 9.1 volts at 70° F. Technician A says the battery has failed the capacity test. Technician B says battery voltage readings will increase as temperature decreases. Who is correct?
Correct Answer
A. Technician A
Explanation
Answer A is correct. If the capacity voltage goes below 9.6 volts at 70° F the battery has failed the capacity test.
Answer B is wrong. The voltage reading gets lower as the outside temperature drops.
Answer C is wrong. Technician A is correct.
Answer D is wrong. Technician A is correct.
23.
A vacuum gauge is connected to the intake manifold of an engine. The needle fluctuates between (15 in. Hg and 20 in. Hg) at idle. This reading indicates:
Correct Answer
A. A sticking valve or misfire.
Explanation
Answer A is correct. If the gauge readings fluctuate between (15 and 20 in Hg) this indicates a stuck valve or engine miss.
Answer B is wrong. If the gauge reads low (15-20 in Hg) this indicates late valve or ignition timing, leaking manifold gasket, low compression, leaking carburetor, or stuck throttle valve.
Answer C is wrong. If the gauge reads steady (17-22 in Hg) this indicates a normal running engine.
Answer D is wrong. If the gauge reading drops slowly at an idle this indicates a clogged or blocked exhaust.
24.
A power balance test is being performed. Technician A says to note the engine RPM before and during the test for each cylinder. Technician B says to record the RPM drop for each cylinder. Who is right?
Correct Answer
B. Technician B
Explanation
Technician B is correct because recording the RPM drop for each cylinder during a power balance test helps to identify which cylinders are not performing as expected. The purpose of the test is to determine how each cylinder affects engine performance by observing changes in RPM when individual cylinders are temporarily disabled or tested. Technician A’s method of noting RPM before and during the test is less specific to the test’s goal.