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8.1 Answer the following questions with reference to an exhaust gas analysis - NSC Mechanical Technology Automotive - Question 8 - 2021 - Paper 1
Question 8
8.1 Answer the following questions with reference to an exhaust gas analysis. 8.1.1 State TWO causes of a low CO2 exhaust gas reading. 8.1.2 State TWO corrective m... show full transcript
Worked Solution & Example Answer:8.1 Answer the following questions with reference to an exhaust gas analysis - NSC Mechanical Technology Automotive - Question 8 - 2021 - Paper 1
Step 1
8.1.1 State TWO causes of a low CO2 exhaust gas reading.
Answer
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A too rich air/fuel mixture can lead to incomplete combustion, resulting in lower CO2 levels in the exhaust.
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A misfire in the ignition system, such as a faulty spark plug, can cause unburnt fuel to exit the cylinder, also contributing to low CO2 readings.
Step 2
8.1.2 State TWO corrective measures for the causes stated in QUESTION 8.1.1.
Answer
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Adjusting the fuel mixture to ensure it is not too rich can help restore normal combustion and increase CO2 emissions.
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Replacing or servicing the faulty spark plug or ignition system component will help achieve a complete combustion and thus improve CO2 levels.
Step 3
8.2 State TWO exhaust gas readings, as detected by a gas analyser, which are caused by a lean air/fuel mixture.
Answer
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High levels of oxygen (O2) in the exhaust, indicating excess unburnt oxygen due to insufficient fuel.
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High carbon dioxide (CO2) levels may also occur as a byproduct of lean conditions.
Step 4
8.3 State ONE cause and ONE corrective measure for the following cylinder leakage test results: 8.3.1 Hissing sound at the exhaust pipe.
Answer
Cause: A leaking exhaust valve allows exhaust gases to escape, creating a hissing sound.
Corrective Measure: Replace the exhaust valve to ensure proper sealing during combustion.
Step 5
8.3 State ONE cause and ONE corrective measure for the following cylinder leakage test results: 8.3.2 Bubbles in the radiator water.
Answer
Cause: A blown head gasket can allow combustion gases to leak into the cooling system, resulting in bubbles in the radiator.
Corrective Measure: Replace the blown head gasket to restore integrity between the combustion chamber and the cooling system.
Step 6
8.4 Explain why an internal combustion engine should be at normal operating temperature when diagnostic tests are performed.
Answer
An internal combustion engine needs to be at normal operating temperature for diagnostic tests to ensure accurate readings. At this temperature, the engine's components expand properly, oil viscosity stabilizes, and the catalytic converter functions effectively, providing reliable data on the engine's performance and emissions.
Step 7
8.5 Complete the table below by writing down the question numbers (8.5.1 to 8.5.4) and the answer in the ANSWER BOOK.
Answer
8.5.1 - Replace fuel filter.
8.5.2 - Renew or disconnect and blow out restricted fuel lines.
8.5.3 - Clean or replace the pump fuel strainer.
8.5.4 - Check and correct the voltage to the fuel pump.
Step 8
8.6 State THREE manufacturer’s specifications required before an oil pressure test can be done.
Answer
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The oil pressure specification when the engine is cold.
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The acceptable oil pressure range when the engine is idling.
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The acceptable oil pressure range when the engine is operating at high revolutions.
Step 9
8.7 Explain FOUR steps to perform a radiator cap pressure test.
Answer
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Obtain the radiator cap's opening pressure specifications, which are usually stamped on the cap.
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Install the cap onto the adapter of the cooling system pressure tester.
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Pump up the tester while monitoring the pressure gauge to ensure it reaches the specified level.
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Note the reading when the pressure is released; this indicates whether the cap is maintaining proper pressure.