Four-Stroke Combustion Cycle and Engine Vacuum Quiz

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What is the effect of decreasing volume of the cylinder during the combustion cycle?

No effect on pressure

Increase in temperature

Increase in pressure (correct)

Decrease in pressure

How does abnormal combustion impact engine performance?

Has no effect on performance

Improves performance

Reduces performance (correct)

Stabilizes engine operation

What is the normal range of engine vacuum at idle?

0-5 inches Hg

15-22 PSI

15-22 inches Hg (correct)

1-10 PSI

Why should fuel and ignition systems be disabled during cranking compression testing?

To prevent injury or component damage Signup and view all the answers

What is the purpose of cranking the engine through one compression stroke during compression testing?

To record PSI Signup and view all the answers

How can poor cylinder seal affect engine performance?

Reduce combustion pressure and performance Signup and view all the answers

What does the Knock Sensor do?

Sends an AC voltage signal to the PCM Signup and view all the answers

How does the Mass Air Flow (MAF) Sensor respond to changes in air density?

More current is required to maintain temperature of the conductor Signup and view all the answers

What function does the Throttle Position (TP) Sensor primarily control?

Transmission shifting schedule Signup and view all the answers

Which sensor is responsible for adjusting the air-fuel ratio based on air density?

Intake Air Temperature (IAT) Sensor Signup and view all the answers

What is the purpose of the Fuel Tank Pressure Sensor?

Detects leaks in the fuel tank Signup and view all the answers

How does the Manifold Absolute Pressure (MAP) Sensor respond to low manifold pressure?

Sensor voltage decreases Signup and view all the answers

What role does the Ignition Reference Signals play in engine control?

Spark timing and injector triggering Signup and view all the answers

What should the first 'puff' pressure reading be in relation to the reading after 4 'puffs' during cranking compression analysis?

At least 50% of the reading after 4 'puffs' Signup and view all the answers

What does low pressure on the first 'puff' and inconsistent pressure build indicate during cranking compression analysis?

Piston ring sealing problem Signup and view all the answers

What is the recommended test to verify low compression in an engine?

Wet compression test Signup and view all the answers

What could be indicated by low compression that doesn’t build up on remaining 'puffs' and does not improve with a wet test?

Leaking valves, hole in piston, or head gasket leak Signup and view all the answers

What can be suspected when there is low compression in two adjacent cylinders?

Leaking head gasket Signup and view all the answers

What is the purpose of a Cylinder Leakage test?

Isolate the cause of low compression Signup and view all the answers

What should be done during a Cylinder Leakage test to isolate the cause effectively?

Introduce pressurized air and listen for leakage Signup and view all the answers

When should the Cylinder Leakage test be performed?

When Cranking Compression Analysis shows low compression Signup and view all the answers

What should be the position of the piston during the Cylinder Leakage test for it to be effective?

Top Dead Center (TDC) on compression stroke Signup and view all the answers

Why is it recommended for the engine to be warm during the Cylinder Leakage test?

To ensure accurate results Signup and view all the answers

What does the PCM stand for in the automotive context?

Powertrain Control Module Signup and view all the answers

Which component is responsible for converting CO, HC, and NOx into water, carbon dioxide, and nitrogen in a vehicle?

CAT Signup and view all the answers

What does the AIR system provide to the exhaust stream to help lower HC & CO emissions?

Oxygen Signup and view all the answers

What is the purpose of the ORVR system in a vehicle?

Prevent fuel vapors from escaping during refueling Signup and view all the answers

What does PCM use to control the air/fuel ratio based on O2 feedback when the engine is at specified temperature?

O2 sensor information Signup and view all the answers

Which type of memory found in PCM stores temporary data but gets erased when power is lost?

RAM Signup and view all the answers

In which mode of operation does the PCM determine an initial air/fuel ratio and deliver one injector pulse per RPM reference pulse?

Open Loop Signup and view all the answers

What is the main role of the PCV system in a vehicle?

To control crankcase pressure and reduce buildup of moisture and acids Signup and view all the answers

What is the purpose of the serial data transmitted by ECMs in vehicles?

To communicate information between vehicle components Signup and view all the answers