Question 1

A rich air-fuel mixture could cause a catalytic converter to overheat and melt.

Accepted Answer

A rich air-fuel mixture can cause an increase in the temperature of the exhaust gases, which may result in the catalytic converter overheating and melting.

Question 2

Technician A says if you remove the PCV valve from the valve cover and plug the end with your finger, the idle will increase if the valve is good. Technician B says that when you block the flow to the PCV valve, it will richen the air-fuel mixture. Which technician is correct?

Accepted Answer

B

Question 3

List several causes of engine overheating.

Accepted Answer

Overheating can be caused by a water pump with a loose or corroded impeller. Check the pump flow by holding the top radiator hose with the engine running and the thermostat open at normal operating temperature. The surge of the coolant can be felt when the engine is accelerated. Besides obvious cooling system problems, overheating can be caused by retarded ignition timing, a partially blocked catalytic converter or exhaust system, or even by detonation due to an inoperative EGR valve.

Question 4

Oil leaks are being discussed. Technician A says a blue lamp can be used to locate an oil leak after a dye has been installed in the crankcase. Technician B says it is a black light that is used. Which technician is correct?

Accepted Answer

The answer of Oil leaks are being discussed. Technician A...

Question 5

When does preignition occur?

Accepted Answer

The answer of When does preignition occur?...

Question 6

Highway driving can result in extra fuel and water dilution in the oil.

Accepted Answer

Highway driving typically results in less fuel and water dilution in the oil compared to short trips or city driving, as the engine operates at a steady, optimal temperature, allowing for better combustion and evaporation of contaminants.

Question 7

Oil consumption problems are being discussed. Technician A says a lack of regular services can cause the oil control rings to plug. Technician B says worn compression rings can cause oil consumption problems. Who is correct?

Accepted Answer

Both technicians are correct. A lack of regular services can cause the oil control rings to plug, leading to oil consumption problems. Worn compression rings can also cause oil consumption issues since they allow oil to slip past them into the combustion chamber.

Question 8

Engine operation is being discussed. Technician A says preignition can cause engine damage. Technician B says carbon deposits on the pistons can increase the compression ratio. Who is correct?

Accepted Answer

Both statements are correct. Preignition can indeed cause engine damage by igniting the fuel-air mixture before the intended spark, leading to excessive heat and potential damage. Carbon deposits on the pistons can effectively reduce the combustion chamber volume, thereby increasing the compression ratio, which can lead to issues such as knocking or preignition.

Question 9

Technician A says carbon removal additives can damage the muffler. Technician B says if the rpm rises when shorting a cylinder out, it could indicate a vacuum leak. Which technician is correct?

Accepted Answer

Carbon removal additives are not known to damage mufflers. Additionally, shorting out a cylinder would not indicate a vacuum leak, but rather an issue with that specific cylinder.

Question 10

Technician A says grounding out a plug wire to a cylinder with a cracked piston will can increase the noise. Technician B says a rod knock will become quieter as its cylinder is grounded. Who is correct?

Accepted Answer

Grounding out a plug wire to a cylinder with a cracked piston can indeed increase the noise, as it changes the combustion dynamics and can make any mechanical issues more audible. Similarly, a rod knock, which is a deep rapping noise that speeds up with engine RPM, can become quieter as its cylinder is grounded because grounding out the spark plug wire effectively disables that cylinder, reducing the forces acting on the rod and thus the noise it produces.

Question 11

An infrared analyzer can be used to check the radiator for combustion leaks.

Accepted Answer

An infrared analyzer can detect the presence of combustion gases, such as carbon monoxide, in the radiator coolant which indicate that there may be a leak in the cooling system.

Question 12

During a compression test, a cylinder shows lower readings than expected. Technician A squirts a tablespoon of oil into the cylinder and the compression raises. He says this indicates a problem with the rings. Technician B says a running compression test should be about one-quarter of that of a cranking compression test. Which technician is correct?

Accepted Answer

If adding oil to the cylinder causes the compression to raise, it indicates that there is a problem with the rings. This is because the oil helps to create a better seal between the rings and the cylinder walls, temporarily increasing compression. Technician B is incorrect as there is no set ratio of running compression test to cranking compression test.

Question 13

Technician A says an indication of preignition could be a hole burned in the center of a piston. Technician B says detonation is an explosion inside the cylinder. Which technician is correct?

Accepted Answer

Both statements are correct. Preignition can indeed lead to a hole being burned in the center of a piston due to the air-fuel mixture igniting too early and causing excessive heat. Detonation refers to an uncontrolled and explosive ignition of the fuel-air mixture within the cylinder, which can cause significant engine damage.

Question 14

Technician A says that an air-fuel mixture that is too lean can cause burned internal engine parts. Technician B says an overly rich mixture can cause oil wash from cylinder walls. Which technician is correct?

Accepted Answer

Both technicians are correct. A lean mixture can cause higher temperatures in the combustion chamber, leading to burnt internal engine parts. Conversely, if the mixture is too rich, unburned fuel can wash away the oil film on the cylinder walls, leading to increased engine wear.

Question 15

Comparing premium fuel to regular fuel, the burn time of premium fuel is _____.

Accepted Answer

Premium fuel has a higher octane rating, which means it burns slower and more efficiently than regular fuel. This leads to a longer burn time and can result in better performance and fuel economy for high-performance engines.

Question 16

If an engine will not turn over in either direction, it could be due to a broken crankshaft.

Accepted Answer

A broken crankshaft can prevent the engine from turning over in either direction.

Question 17

An engine exhibits a low, steady vacuum reading. This could indicate _____.

Accepted Answer

The answer of An engine exhibits a low, steady vacuum...

Question 18

Excessive clearance at a connecting rod bearing journal will cause a rod knock.

Accepted Answer

Excessive clearance at a connecting rod bearing journal allows the rod to move around excessively, causing it to knock against the crankshaft. This is commonly known as a "rod knock".

Question 19

Technician A says a faulty head gasket can cause the oil to mix with coolant. Technician B says this is called cross fluid contamination. Which technician is correct?

Accepted Answer

Technician A is correct in stating that a faulty head gasket can cause the oil to mix with coolant. Technician B is also correct in saying that this is called cross fluid contamination. Therefore, both technicians are correct.

Question 20

Technician A says that valvetrain noise will occur at half the speed of engine rpm. Technician B says valvetrain noises coming from inside the timing cover can be caused by a bad timing chain or chain guide. Which technician is correct?

Accepted Answer

Valvetrain noise occurs at half the speed of engine rpm because the camshaft, which operates the valves, turns at half the speed of the crankshaft. Technician B is correct because a bad timing chain or chain guide can indeed cause noises from inside the timing cover, as these components are crucial for the timing and operation of the valvetrain.

Quiz 3: Diagnosing Engine Problems