32 Questions
What is the effect of decreasing volume of the cylinder during the combustion cycle?
Increase in pressure
How does abnormal combustion impact engine performance?
Reduces performance
What is the normal range of engine vacuum at idle?
15-22 inches Hg
Why should fuel and ignition systems be disabled during cranking compression testing?
To prevent injury or component damage
What is the purpose of cranking the engine through one compression stroke during compression testing?
To record PSI
How can poor cylinder seal affect engine performance?
Reduce combustion pressure and performance
What does the Knock Sensor do?
Sends an AC voltage signal to the PCM
How does the Mass Air Flow (MAF) Sensor respond to changes in air density?
More current is required to maintain temperature of the conductor
What function does the Throttle Position (TP) Sensor primarily control?
Transmission shifting schedule
Which sensor is responsible for adjusting the air-fuel ratio based on air density?
Intake Air Temperature (IAT) Sensor
What is the purpose of the Fuel Tank Pressure Sensor?
Detects leaks in the fuel tank
How does the Manifold Absolute Pressure (MAP) Sensor respond to low manifold pressure?
Sensor voltage decreases
What role does the Ignition Reference Signals play in engine control?
Spark timing and injector triggering
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'
What does low pressure on the first 'puff' and inconsistent pressure build indicate during cranking compression analysis?
Piston ring sealing problem
What is the recommended test to verify low compression in an engine?
Wet compression test
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
What can be suspected when there is low compression in two adjacent cylinders?
Leaking head gasket
What is the purpose of a Cylinder Leakage test?
Isolate the cause of low compression
What should be done during a Cylinder Leakage test to isolate the cause effectively?
Introduce pressurized air and listen for leakage
When should the Cylinder Leakage test be performed?
When Cranking Compression Analysis shows low compression
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
Why is it recommended for the engine to be warm during the Cylinder Leakage test?
To ensure accurate results
What does the PCM stand for in the automotive context?
Powertrain Control Module
Which component is responsible for converting CO, HC, and NOx into water, carbon dioxide, and nitrogen in a vehicle?
CAT
What does the AIR system provide to the exhaust stream to help lower HC & CO emissions?
Oxygen
What is the purpose of the ORVR system in a vehicle?
Prevent fuel vapors from escaping during refueling
What does PCM use to control the air/fuel ratio based on O2 feedback when the engine is at specified temperature?
O2 sensor information
Which type of memory found in PCM stores temporary data but gets erased when power is lost?
RAM
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
What is the main role of the PCV system in a vehicle?
To control crankcase pressure and reduce buildup of moisture and acids
What is the purpose of the serial data transmitted by ECMs in vehicles?
To communicate information between vehicle components
Test your knowledge on the effects of compression in the four-stroke combustion cycle, abnormal combustion, volumetric efficiency, combustion chamber design, and engine vacuum. Learn about the significance of manifold vacuum tests in diagnosing various engine mechanical conditions.
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