8.1 State THREE gas analyser readings that are caused by a faulty catalytic converter - NSC Mechanical Technology Automotive - Question 8 - 2022 - Paper 1

To determine the causes of leakages on an internal combustion engine, the following methods can be employed:

1. Listening for hissing sounds at the air intake - This helps identify if air is escaping, which could mean leaks in the intake manifold.
2. Listening for hissing from the dipstick hole or oil filler cap - This can indicate blow-by of gases, suggesting worn piston rings.
3. Checking for bubbles in the radiator water - Bubbles may point to a blown head gasket, as combustion gases escape into the cooling system.

To find the allowable variation in percentage, use the formula:

ext{Variation} = rac{( ext{Highest reading} - ext{Lowest reading})}{ ext{Highest reading}} imes 100

In this case, the highest reading is 11 bar (Cylinder 1) and the lowest reading is 8.2 bar (Cylinder 3):

ext{Variation} = rac{11 - 8.2}{11} imes 100 = 25.5\\%

Thus, the allowable variation is 25.5%.

The maximum variation can be calculated using:

$ext{Maximum variation} = ext{Highest reading} - ext{Lowest reading}$

From the readings:

• Highest reading = 11 bar (Cylinder 1)
• Lowest reading = 8.2 bar (Cylinder 3)

$ext{Maximum variation} = 11 - 8.2 = 2.8 ext{ bar}$

Thus, the maximum variation is 2.8 bar.

Two possible causes for the low reading in Cylinder 3 (8.2 bar) are:

1. Worn compression rings - This can lead to loss of cylinder pressure as the rings fail to seal effectively.
2. Leaking head gasket - A compromised gasket can allow gases to escape or coolant to enter the cylinder, reducing compression.

If the wet test does not impact the reading for Cylinder 3, the following corrective measures should be taken:

1. Repair or replace the cylinder head - This will address any leakage issues from the head that could be affecting compression.
2. Replace piston rings - If the compression rings are worn or damaged, replacing them will restore proper compression.

Possible causes of low oil pressure include:

1. Worn oil pump - A failing pump may not be generating enough pressure to circulate oil effectively.
2. Clogged oil filter - If the filter is blocked, it can impede oil flow, leading to reduced pressure.

To correct high oil pressure, consider the following actions:

1. Change the oil to the correct viscosity - Using the recommended oil grade can help regulate pressure more effectively.
2. Check for a malfunctioning oil pressure relief valve - Ensure the valve is operating properly and replace if necessary.

Before connecting the fuel pressure tester, ensure to:

1. Verify if the tester can read the pressure of the engine accurately.
2. Use the right adaptor - Make sure the tester is compatible with the engine's fuel system.
3. Check the rubber pipe for any signs of wear or damage to avoid leaks during testing.

If the pressure in the cooling system drops, the following corrective measures should be taken:

1. Renew the faulty water hose - This ensures that any leak in the hose is addressed.
2. Replace the failure radiator - If the radiator is leaking or damaged, it needs to be replaced.
3. Inspect and renew the heater cap - A faulty cap can cause pressure loss, leading to cooling system failure.