# Engine Mechanical - Ss

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Atahcpss
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Quizzes Created: 39 | Total Attempts: 144,025
Questions: 15 | Attempts: 612

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• 1.

### The process of mechanical testing will first help you identify the location of a mechanical problem and then identify the cause of the fault.

• A.

True

• B.

False

A. True
Explanation
The statement is true because mechanical testing is a systematic process that involves various techniques and tools to identify and analyze mechanical problems in a system or component. By conducting mechanical tests, such as stress tests, vibration tests, or load tests, engineers can determine the location of the problem and understand its root cause. This helps in troubleshooting and finding effective solutions to rectify the fault. Therefore, mechanical testing plays a crucial role in identifying and diagnosing mechanical problems.

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• 2.

### What unit of measure is used when testing engine compression and cylinder leakage?

• A.

Pounds per square inch (psi)

• B.

Kilopascals (kPa)

• C.

Both A and B

• D.

Pound feet

C. Both A and B
Explanation
Both pounds per square inch (psi) and kilopascals (kPa) are units of measure used when testing engine compression and cylinder leakage. These units are used to measure the pressure within the engine cylinders, which can indicate the overall health and efficiency of the engine. The use of both units allows for flexibility and compatibility with different testing equipment and standards.

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• 3.

### Which of the following methods may be used to manually perform a cylinder power balance test?

• A.

Unplug the ignition from each cylinder.

• B.

Unplug the fuel injectors.

• C.

Both A and B

• D.

None of the above

C. Both A and B
Explanation
To perform a power balance test, either the ignition or the fuel can be disabled.

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• 4.

### When testing intake manifold vacuum, the gauge needle oscillates back and forth rapidly, which generally indicates:

• A.

A partially restricted exhaust

• B.

A mechanical condition such as a burned or bent valve.

• C.

Late ignition or valve timing.

• D.

None of the above

B. A mechanical condition such as a burned or bent valve.
Explanation
The needle oscillations are an indication of an internal mechanical fault, which occurs as rapidly as the engine turns.

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• 5.

### How even should the cranking compression be between the lowest and highest cylinder readings on an engine without mechanical problems?

• A.

Within 5%

• B.

Within 3%

• C.

Within 14%

• D.

Within 10%

D. Within 10%
Explanation
The cranking compression between the lowest and highest cylinder readings on an engine without mechanical problems should be within 10%. This means that the compression readings of each cylinder should not differ by more than 10%. If the difference is greater than 10%, it could indicate potential mechanical issues in the engine, such as worn piston rings or valves.

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• 6.

### Which of the following malfunctions would be revealed during a running compression test?

• A.

A burned exhaust valve

• B.

• C.

Both A and B

• D.

None of the above

C. Both A and B
Explanation
During a running compression test, both a burned exhaust valve and a badly worn camshaft lobe would be revealed as malfunctions. A running compression test involves measuring the pressure inside the cylinders while the engine is running. A burned exhaust valve can cause a loss of compression, resulting in lower pressure readings. Similarly, a badly worn camshaft lobe can lead to improper valve timing and reduced compression. Therefore, both of these malfunctions would be detected during a running compression test.

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• 7.

### When checking cranking compression, which of the following malfunctions is either confirmed or ruled out by performing a wet test on a cylinder with low compression?

• A.

A small hole in the top of the piston

• B.

A burned exhaust valve

• C.

• D.

None of the above

D. None of the above
Explanation
A wet compression test validates the seal provided by the piston rings.

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• 8.

### When performing a cylinder leakage test, a small amount of air leakage can be heard from the exhaust tail pipe. This indicates:

• A.

Worn valve guides.

• B.

• C.

A bent intake valve.

• D.

Explanation
A leak heard from the associated part of the compression chamber will lead you to the bad sealing component.

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• 9.

### When testing cranking compression, Tech A says that all engines may be disabled to avoid starting by placing a shop rag in the engine intake. Tech B says that an engine may be disabled by removing the fuel pump relay (if equipped). Who is correct?

• A.

Tech A

• B.

Tech B

• C.

Both Techs A and B

• D.

Neither Tech A nor B

B. Tech B
Explanation
All engines should be disabled by removing fuel delivery from the engine.

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• 10.

### Which of the following can be measured by a running compression test, but NOT by a cranking compression test?

• A.

The sealing capability of the valves

• B.

The sealing capability of the rings and pistons

• C.

• D.

None of the above

D. None of the above
Explanation
A running compression test measures the compression pressure in the cylinders while the engine is running. This test can provide information about the sealing capability of both the valves and the rings and pistons. It can also detect issues with bad piston rings. Therefore, all of the options listed can be measured by a running compression test, making the correct answer "None of the above".

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• 11.

### When performing a cranking compression test, Tech A says the final reading should be reached on the second compression pulse. Tech B says the first compression pulse should read at least half as much as the final reading. Who is correct?

• A.

Tech A

• B.

Tech B

• C.

Both Techs A and B

• D.

Neither Tech A nor B

B. Tech B
Explanation
Tech B is correct. During a cranking compression test, the first compression pulse should read at least half as much as the final reading. This is because the first pulse represents the initial compression of the engine, while the final reading represents the maximum compression achieved. The first pulse should not be significantly lower than half of the final reading, as this could indicate issues with the engine's compression. Therefore, Tech B's statement is accurate.

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• 12.

### Techs A and B are discussing how to obtain the most accurate results when testing cranking compression on a gasoline engine. Tech A says the battery must be at least half charged. Tech B says at least three compression pulses should be made on each cylinder while watching the gauge. Who is correct?

• A.

Tech A

• B.

Tech B

• C.

Both Techs A and B

• D.

Neither Tech A nor B

D. Neither Tech A nor B
Explanation
Neither Tech A nor Tech B is correct. The accuracy of cranking compression testing on a gasoline engine does not depend on the battery being at least half charged. Additionally, while making at least three compression pulses on each cylinder can provide more consistent results, it does not guarantee the most accurate results. Other factors such as engine temperature, throttle position, and the condition of the engine components can also affect the accuracy of the test. Therefore, both Tech A and Tech B are incorrect.

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• 13.

### When leak-down testing a cylinder with high leakage, air escaping from the spark plug hole of an adjacent cylinder would indicate a possible?

• A.

Hole in the piston

• B.

Intake valve

• C.

Exhaust valve

• D.

Explanation
If air is escaping from the spark plug hole of an adjacent cylinder during leak-down testing, it indicates a possible issue with the head gasket. The head gasket is responsible for sealing the combustion chamber and preventing any leakage between cylinders. If there is a leak in the head gasket, air can escape from one cylinder to another, causing the adjacent cylinder to show signs of leakage. This can be a potential cause of high leakage in the cylinder being tested.

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• 14.

### In order to leak check a cylinder, the piston must be on the intake stroke.

• A.

True

• B.

False

B. False
Explanation
To leak check a cylinder, the piston must be on the compression stroke, not the intake stroke. During the compression stroke, the piston moves upward, compressing the air-fuel mixture in the cylinder. This creates the necessary pressure for detecting any leaks in the cylinder. On the other hand, during the intake stroke, the piston moves downward to allow the air-fuel mixture to enter the cylinder, which is not suitable for leak checking. Hence, the statement is false.

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• 15.

### When diagnosing an engine misfire, what test is used to determine the misfiring cylinder?

• A.

Engine vacuum test

• B.

Power balance test

• C.

Cranking compression test

• D.

Cylinder leak-down test

B. Power balance test
Explanation
The power balance test is used to determine the misfiring cylinder when diagnosing an engine misfire. This test involves temporarily disabling each cylinder one at a time while the engine is running and observing the change in engine RPM. If there is a significant drop in RPM when a specific cylinder is disabled, it indicates that the cylinder is not contributing its fair share of power and is likely the misfiring cylinder. This test helps identify the specific cylinder that is causing the misfire, allowing for targeted repairs or troubleshooting.

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• Current Version
• Mar 20, 2023
Quiz Edited by
ProProfs Editorial Team
• Oct 01, 2015
Quiz Created by
Atahcpss

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