8.1 TABLE 8.1 below shows the results of the gas analysis of an internal combustion engine - NSC Mechanical Technology Automotive - Question 8 - 2023 - Paper 1
Question 8
8.1 TABLE 8.1 below shows the results of the gas analysis of an internal combustion engine. Complete TABLE 8.1 by giving ONE cause and ONE appropriate corrective mea... show full transcript
Worked Solution & Example Answer:8.1 TABLE 8.1 below shows the results of the gas analysis of an internal combustion engine - NSC Mechanical Technology Automotive - Question 8 - 2023 - Paper 1
Step 1
8.1 Complete TABLE 8.1
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Answer
High oxygen (O2) reading:
Cause: Too lean air-fuel ratio.
Corrective Measure: Reset fuel mixture.
High hydrocarbon (HC) reading:
Cause: Excessive unburnt fuel.
Corrective Measure: Reset fuel mixture.
Step 2
8.2.1 Remove the high-tension lead.
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Answer
This step is necessary to prevent distribution of high voltage, ensuring safety and avoiding electrical shocks during the testing process.
Step 3
8.2.2 Unplug the fuel-injection system.
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Unplugging the fuel-injection system prevents fuel from entering the exhaust system, which is essential for accurate compression testing.
Step 4
8.2.3 Fully open the throttle valve.
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This allows the correct amount of air to enter the cylinder, ensuring that the readings obtained are accurate and reflect the engine's actual performance.
Step 5
8.2.4 Record the readings.
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Recording the readings is crucial for comparing them with specifications and determining if the engine is functioning correctly.
Step 6
8.3.1 Hissing sound at the air intake.
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Cause: Leaking inlet valves.
Corrective Measure: Replace or reseal the valves.
Step 7
8.3.2 Hissing sound at the dipstick.
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Cause: Worn piston rings.
Corrective Measure: Overhaul the engine and fit new pistons.
Step 8
8.4 State THREE causes of a high oil-pressure reading.
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Blocked oil passages.
Too little crankshaft bearing clearance.
Contaminated oil.
Step 9
8.5.1 State TWO manufacturer’s specifications required before the fuel pressure test can be conducted.
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Fuel pressure after the fuel pump.
Fuel pressure when the engine is idling.
Step 10
8.5.2 Where on the vehicle is the fuel-pressure tester inserted?
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The fuel-pressure tester is fitted to the fuel line.
Step 11
8.5.3 Why may the rubber pipe on the fuel pressure tester not be worn?
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A worn rubber pipe could lead to fuel leakage, inaccurate results, and pose a fire hazard.
Step 12
8.6 State FOUR causes of pressure drop during a cooling system pressure test.
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Coolant leaks from between gaskets/seals of the cooling system.
