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Page 4 Keywords
Page 5 Environment protection Page 7 Australian design rules
Page 9 Fuel types used
Page 12 Emission control systems Page 13 Evaporative systems
Page 16 Positive crankcase ventilation Page 17 Exhaust emission controls Page 28 Air intake system
Page 33 Fuel injection systems Page 33 Air injection systems
Page 34 Section Overview Page 35 Review Questions One
Page 40 Safety when servicing vehicles Page 42 Protective clothing
Page 43 Using lifting equipment
Page 46 Emission components inspections Page 58 Section Overview
Page 59 Review Questions Two
Page 61 Elements and Performance Criteria
What is the objective of this unit?
To inspect and service emission control systems. What is this unit about?
It’s about these elements:
Prepare to inspect and service emission control system. Inspect emission control system.
Service emission control system. Complete work processes. How will I be assessed?
Assessment will take place when you are confident that you have acquired the skills and the underpinning knowledge necessary to successfully complete the unit. Practical skill assessment will take place only after a period of supervised practiced and repetitive experience. You must be able to meet all the requirements of this unit without direct supervision.
Where can I find the Elements and Performance Criteria? At the back of this workbook.
It is recommended that students learn the meaning and the correct spelling of the following key words that are particularly relevant to these unit standards.
Exhaust Emission Evaporation
Pressure Vacuum Fuel
Charcoal Canister Ventilation
Crankcase Valve Carburettor
Sensor Switch Recirculation
It is recommended that you are familiar with the following words and their definitions to help your understanding of the material contained in this workbook.
Evaporation: To change into a vapour/steam Deterioration: A gradual decline in quality
Ambient: Surrounding air – room temperature Mandatory: A requirement, a must do
Conjunction: Combination, joining together Residual: Left over at the end
Fluctuation: Continual change from one state to another Compress: To force together
Incombustible: Cannot not burn Pulsates: Shakes
Dissipate: To loose or spread out in different directions Instantaneous: Immediate
Optimum: Ideal, best. KEY WORDS
Limiting harm to the environment is a very important consideration for vehicle manufacturers. As well as having to comply with environmental laws the general motoring public are much more conscious of the environment when deciding on which vehicle to purchase.
As well as improvements to exhaust emissions manufacturers are moving to more environmentally friendly fuels and construction materials.
Exhaust emission controls are designed to reduce the amount of harmful gases released through the exhaust system into the atmosphere.
Typically vehicles without an emission control systems will emit gases from three main areas – the exhaust (60%), the crankcase (30%) and the fuel tank (10%). Vehicle emissions are primarily the result of the air and fuel not being completely used up during combustion. As a result, harmful gases are emitted, such as Hydrocarbons (HC), Carbon monoxide (CO) and Oxides of Nitrogen (NOx). Emissions are also caused by the evaporation of fuel contained in the fuel tank.
The main source of pollution from a vehicle is through the exhaust system.
The exhaust is the largest source of vehicle emissions containing three significant air pollutants these are CO-Carbon monoxide, HC-Hydrocarbons and NOx – Nitrogen oxides.
CO-Carbon Monoxide
Carbon monoxide is a tasteless, odourless and poisonous gas that forms during the combustion process due to incomplete combustion, resulting from a lack of oxygen or too much fuel. Carbon monoxide reduces the flow of oxygen in the bloodstream and is particularly dangerous to people with heart disease.
HC- Hydrocarbons
Hydrocarbons are made up of hydrogen and carbon elements. These elements are burned with oxygen during combustion, but all the fuel may not be consumed during this process. This residue comes out the exhaust pipe as hydrocarbons.
Hydrocarbons react in the presence of nitrogen oxides and sunlight to form ground-level ozone, a major component of smog. Ozone irritates the eyes, damages the lungs, and aggravates respiratory problems.
NOx – Nitrogen Oxides
Nitrogen oxides are the result of high combustion temperatures. Too little fuel in the air/fuel ratio causes excessive NOx levels. When exposed to sunlight and combined with unburnt hydrocarbons, NOx creates smog. They also contribute to the formation of acid rain. HC, CO, NOx Air pollutants Smog
Exhaust gas analyser readings
ENVIRONMENT PROTECTION
Earth Ozone layer Stratosphere Ultra high atmosphere Ultra Violet radiation 50km 10km Troposphere Ozone Protection
Ozone is a molecule that contains three oxygen atoms (O3). The common oxygen molecule contains two atoms (O2). Ozone is formed in the upper atmosphere approximately 15 to 20 kilometres above the earth’s surface, known as the stratosphere.
The ozone layer screens out dangerous types of solar radiation. A small decrease within the ozone layer can greatly increase the amount of harmful radiation that reaches earth’s surface.
Ozone is formed by oxygen (O2) molecules being carried up into the atmosphere by convection currents of hot air radiating from the earth’s surface.
The oxygen (O2) molecules are broken down by ultra violet radiation into two single oxygen atoms (O) these atoms then combine with other oxygen molecules (O2) to form an ozone molecule (O3), creating an ozone layer.
An increase in UV radiation reaching the earth’s surface can effect: Phytoplankton
The base of all marine life can be seriously threatened as many fish and marine animals have a surface dwelling larval stage, which can be injured or destroyed by UV radiation. Crop production
Crop production will decline as plant life is scorched; livestock feeding and health will also be at risk.
Increased skin cancers
An increase in skin cancer is likely, as a 1% loss of ozone will lead to a 2% increase in UV radiation reaching the earth’s surface and consequently a 4% increase in skin cancer.
Ozone layer depletion occurs when chlorofluorocarbons (CFC’s) enter the earth’s stratosphere. Once the CFC molecule reaches the stratosphere, UV radiation breaks down the CFC molecule. From this breaking down process a chlorine atom is released, which bonds with an oxygen atom (O2) to form a chlorine monoxide molecule trapping oxygen molecules.
The trapping effect reduces the number of oxygen atoms available for the reformation of the ozone. The result is depletion within the ozone layer and the formation of holes within the ozone layer at the north and South Pole regions, due to winds that hold these pollutants over the poles (known as circum polar vortex).
Unfortunately the chlorine molecule has an expected atmospheric life (EAL) of approximately 100 years and will greatly contribute to the ongoing problem of the Stratosphere Breaks down ultra violet light Skin cancer Chlorine
Heats and warms the earth’s surface CFC’S Halons CO2 NOx Methane Some heat radiation
escapes trap the rest Troposphere
Earth Incoming solar
radiation
Global Warming
The energy that warms and lights the earth is derived from the sun. A large quantity of that energy takes the form of short wave radiation, including visible light. When the earth surface is struck by this energy, the energy changes from light to heat and warms the earth’s surface. The earth’s surface releases some of this heat in the form of long wave infra red radiation.
Most of the long wave infra red radiation deflects back out to space, but a small amount remains trapped within the earth’s atmosphere.
Gases such as methane, carbon dioxide, nitrous oxide (fertilisers) and water vapour (clouds) help provide the trap, absorbing and reflecting these infra red waves radiated by the earth. These gases help to keep the earth inhabitable. Should greenhouse gases increase, more heat energy will remain trapped and the earth will continue to warm and overheat, the result would be a melting of the polar ice caps and a gradual flooding of the earth’s surface.
Scientists have discovered that CFC's in the lower atmosphere, (before they start to deplete ozone in the stratosphere) are highly efficient greenhouse gases. Each molecule of chlorine can trap over 10,000 times more energy than a molecule of carbon dioxide. CFC’s are estimated to contribute over 20% of the greenhouse effect. So as the ozone is depleted, UV radiation penetrates lower, leading to additional warming of the earth’s surface. Highly effective greenhouse gases Infra red radiation
The Department of Transport and Regional Services, the National Road Transport Commission and representatives from the automotive industry in each state have developed performance and design rules for motor vehicle safety, emissions and/or anti-theft.
The main ADR’s that relate to service emission control systems are:
Fuel systems: This rule specifies requirements when using petrol that will ensure safe operation and will reduce the risks of fire as a result of petrol spillage during filling or as a result of an impact.
Diesel engine exhaust smoke emissions: This rule limits the cloudiness of diesel engine exhaust smoke emissions.
Exhaust emission control for heavy duty vehicles: This rule limits exhaust emissions from the engine of heavy duty motor vehicles in order to reduce air pollution.
Emission control for light vehicles: This rule sets limits for the extent of fuel evaporation and exhaust emissions.
Mandatory operations on unleaded petrol: This rule requires vehicles to be manufactured to use unleaded petrol and to have certain features such as filler necks that will not accept a super filler nozzle.
The main ADR’s that relate to service diesel exhaust systems are ADR 79 and ADR 80. These rules require Australian vehicles to be within specified exhaust emission levels in order to reduce air pollution.
The Australian Government is currently considering the case for adopting the more stringent Euro 6 emissions regulations.
A National Environment Protection Measure (Diesel Vehicle Emissions) is also in place. This measure sets out the emission standards, compliance requirements, testing and the process for dealing with vehicles with excessive exhaust emissions.
Limiting harm to the environment is a very important consideration for vehicle manufacturers. As well as having to comply with environmental laws the general motoring public are much more conscious of the environment when deciding on which vehicle to purchase.
As well as improvements to exhaust emissions manufacturers are moving to more environmentally friendly fuels and construction materials.
AUSTRALIAN DESIGN RULES
ADR17 ADR30 ADR36 ADR37 ADR41 EURO 6
Vehicles traditionally used petrol or diesel for motive power. However, as the cost of these fuels has increased and the environmental harm that they cause has become known, vehicle manufacturers have developed technologies to power vehicles using alternative fuels.
PETROL
Petrol is refined from crude oil and is the most common type of automotive fuel. It is a mixture of hydrogen and carbon, and is called a hydrocarbon.
There are many disadvantages associated with petrol, these include:
It is carcinogenic (can cause cancer) if it enters the water supply
It is highly flammable
It produces harmful exhaust emissions when used in the combustion process.
Its supply is reducing and its cost is increasing. DIESEL
Diesel fuel is also refined from crude oil; however it takes less refining and consequently it is usually cheaper than petrol. Diesel fuel has a higher energy density than petrol and provides better fuel efficiency.
This improved fuel efficiency results in lower overall harmful emissions when compared to petrol engines. However; to withstand the higher compression pressures diesel engines have to made of a heavier construction than petrol engines and consequently are more commonly found in commercial vehicles.
BIO-DIESEL
Bio-diesel is a liquid fuel that is refined from animal fats or plant oils and can be used in normal diesel engines. Its main advantages are that it is a renewable fuel (grow more plants) and it is non-toxic. It can be used to fuel buses and commercial vehicles.
Burning bio-diesel contributes no additional CO2 to the atmosphere. A possible disadvantage to bio-diesel is the impact that it may have on food supply, particularly in third world countries. If farmers switch from growing crops for fuel rather than for food, food supply is likely to drop and food prices will most likely increase.
LPG
Liquefied Petroleum Gas (LPG) is refined from crude oil as a clear colourless liquid. Its non-toxic and non-corrosive features make it an attractive cleaner fuel; however it is less energy efficient than petrol or diesel and can only be used with vehicles specifically designed for LPG.
CNG
Compressed Natural Gas; Natural gas is found when drilling for oil. CNG is simply natural gas that is compressed; however as it is a gas it has lower energy efficiency. For this reason it needs a large fuel tank. Natural gas is an energy source that has much lower air emissions than other fossil fuels, such as oil or coal.Natural gas is the world’s cleanest burning fossil fuel and it has emerged as the environmentally preferred fossil fuel of choice.
ETHANOL
Ethanol is becoming an increasingly popular fuel as it can be manufactured using sugar cane or corn. Ethanol only engines can produce similar power and torque to petrol engines. Ethanol also has the added advantage in that it burns clean; however it can be quite corrosive on fuel system components. METHANOL
Methanol has a higher thermal efficiency than petrol and can yield greater power. However it is less fuel efficient and again it can be corrosive to fuel system components. It is a colourless liquid that is poisonous and flammable, although less flammable than petrol.
HYBRID
Hybrid vehicles refer to vehicles that are powered using a combination of electrical batteries to power an electric motor and fuel to power an internal combustion engine.
Depending on the engine set up a wide range of fuels can be used. Hybrid vehicles offer excellent fuel economy.
The hybrid battery is recharged from two sources, the generator powered by the engine and through reclaiming the energy used during braking.
ELECTRIC FUELLED VEHICLES
Electric fuelled vehicles use an electric motor rather than an internal combustion engine and are powered using energy from rechargeable batteries. They produce no exhaust fumes are quiet in operation and are cheap to operate. On the negative side they can have a limited driving range before the batteries need to be recharged, the batteries are expensive and some batteries do not perform well in cold conditions.
HYDROGEN FUEL CELLS
Fuel cells convert hydrogen and oxygen to electricity without going through a combustion process.
As they operate at much higher efficiencies than traditional combustion engines they produce double the amount of energy with very low emissions. At the moment hydrogen tanks are too large for use in cars, however, it is expected that fuel cells will become the most widely used energy source in the future.
URBAN DESIGN
In recent years the numbers of vehicles on our roads has increased significantly as vehicles have become more affordable, roads have improved and more people are working.
This has led to a much more mobile society where many households now have two or even three vehicles at their disposal.
With this increase in vehicles comes increased traffic and costs associated with running vehicles. As a result demand has increased for smaller more fuel efficient vehicles that are easier to park and cheaper to run in busy urban settings.
Emission control systems are installed to vehicles to reduce the levels of harmful exhaust emissions into the atmosphere.
Sensors, valves, switches and regulators are used to monitor, vent and switch the emission control devices on and off, throughout the engine operation range.
The four main emission control systems used in vehicles are the: evaporation
positive crankcase ventilation exhaust emission control systems air intake system
EMISSION CONTROL SYSTEMS
Reduce emissions
Fuel filter high pressure side Pressure regulator PCV valve Injector Solenoid valve pressure regulator Purge control Solenoid Vacuum switch valve Distributor ECU Vacuum delay valve Orifice
Throttle sensor and idle switch
Air valve EGR control valve
Water thermo switch
Orifice EGR modulator valve Solenoid valve EGR Solenoid valve idle speed control Catalytic converter Water thermo valve Oxygen sensor Water thermo sensor
Intake air thermo sensor Air flow
meter Fuel pump Fuel filter low pressure side
Three-way check valve
No.2 purge
control valve No.1 purge control valve Exhaust gas Vacuum Fuel Air Other
The evaporation control system is designed to prevent fuel vapours from evaporating into the atmosphere by preventing fuel vapour build up in the sealed fuel tank.
The evaporative system is made up of the following: Fuel tank and fuel lines
Fuel cap Roll over valve Carbon canister
Purge control valve/Solenoid
Fuel Tank and Fuel Lines
An automotive fuel tank is a storage container that is designed to safely contain fuel and to supply fuel on demand to the engine. Fuel tanks are generally mounted at the rear of the vehicle (as far away from the engine as possible).
The fuel tank may be constructed of either steel or plastic and are usually baffled to increase strength and to prevent fuel surging when the vehicle is cornering.
The steel fuel tank is coated with a lead-tin alloy to prevent rusting. The plastic used in plastic fuel tanks must resist fuel deterioration and be strong enough to withstand impact.
A fuel tank Metal Lead Plastic Aluminium EVAPORATION SYSTEMS Evaporative components Fuel tank ECU Inlet manifold
Purge control valve
Charcoal canister Atmospheric port
The fuel tank contains a filler pipe that is designed to only accept the correct fuel pump nozzle size for the vehicle. For example, for a 91 octane fuelled vehicle only a 91 octane fuel nozzle will fit into the fuel tank filler pipe.
An expansion chamber, either inside the fuel tank or as a separate air chamber is installed to ensure that the fuel tank does not completely fill as a result of the expansion rate of the fuel.
A fuel tank sender unit is commonly installed into the fuel tank to measure the amount of fuel within the fuel tank and relay this information electronically to the fuel gauge on the instrument panel. Some manufacturers combine an electric fuel pump with a fuel sender unit to draw out the fuel from the fuel tank and deliver the fuel to the engine.
Fuel lines carry the fuel from the tank to the engine. The fuel pump draws the fuel from the tank, to the engine through the main fuel line. A return fuel line helps cool the fuel and prevents vapour locks.
Fuel lines can be made of steel or plastic (rigid fuel lines) or neoprene or polythene (flexible fuel lines). Steel lines are tinned to prevent corrosion, and must be strong enough to withstand the constant vibration experienced. If steel lines are fitted, they must have a length of flexible hose connected between the body and the engine to allow for the movement between the two.
Fuel Caps
Fuel caps are sealed to prevent the escape of fuel and fuel vapours from the tank. They may contain a pressure and vacuum valve that only open under abnormal conditions of high pressure or vacuum.
The vacuum valve allows atmospheric pressure to enter the fuel tank and act on the fuel within the tank thereby preventing vacuum build up within the tank as result of fuel usage. This vacuum build up would restrict fuel flow.
As the ambient air temperature rises the temperature of the fuel within the fuel tank increases thereby increasing the rate of fuel vaporisation. This increase in the rate of fuel vaporisation results in an increase in pressure within the fuel tank. The fuel cap pressure valve is designed to release this pressure build up by redirecting vapours to a charcoal canister.
Fuel vapours trapped in the sealed fuel tank may also be vented through a vapour valve assembly on top of the tank. The vapours leave the valve assembly through a single vapour line and continue to the charcoal canister for storage until they are purged to the engine for burning.
Rollover Valve
A roll over valve is commonly located in the vapour valve assembly and is designed to Pressure
relief valve
Vapours trapped
A sealed fuel cap
Tank sender unit Steel Plastic Pressure and vacuum valve
Fuel vapour Check valve Charcoal canister Intake manifold vacuum reservoir Fuel tank PCM To throttle body Open to atmosphere From fuel tank port To inlet manifold port
Vacuum purge valve Charcoal canister
Charcoal Canister
The charcoal canister is a cylindrical shaped container that contains active carbon charcoal to trap and hold fuel vapours. It can have two or three ports on top of the canister. In the case of a two port canister, one port is connected to the fuel tank while the other port is connected to the inlet manifold. The three port canister will have an additional port that is connected to a vacuum signalling solenoid or valve.
A filter located at the bottom of the canister filters the pressurised fuel vapour and allows the filtered air to escape through the atmospheric port. When a vacuum is created within the fuel tank (as the fuel level drops) the vacuum draws in air through the atmospheric port and allows the fuel tank to breathe.
Purge Control Valve/Solenoid
The purge control valve/solenoid when activated releases the fuel vapours stored in the charcoal canister into the inlet manifold. The purge control valve/solenoid can be either vacuum or ECU operated. Cylindrical shaped Purge solenoid Purge control Air filter
A positive crankcase ventilation valve
The positive crankcase ventilation system is designed to re-introduce fuel vapours that have pressurised in the crankcase, to the engine for recirculation. These vapours build up as a result of engine blow-by and if not redirected into the engine the vapours will be emitted into the atmosphere. Although some crankcase emissions are released into the atmosphere, the extent of this release is significantly reduced by the positive crankcase ventilation valve.
Positive Crankcase Ventilation Valve (PCV valve) The PCV valve is designed to release pressure and vapours from the crankcase by directing them back into the inlet manifold where they can be burnt in the cylinder.
These pressures and vapours in the crankcase are residual gases that have escaped past the piston rings and collect into the crankcase during the combustion process.
The PCV valve controls the release of crankcase gases and vapours to the inlet manifold. When the engine is at rest a tension spring
keeps the valve closed.
When the engine is running it produces a vacuum, this vacuum overcomes the spring tension and opens the valve and releases the gases for burning.
When the vehicle is idling or decelerating, vacuum increases and pulls the valve plunger into the valve opening. This partially blocks off the opening so less gas can be burnt. Re-introduce
fuel vapours
POSITIVE CRANKCASE VENTILATION SYSTEM
Release pressure and vapours Crankcase gases PCV valve Throttle body Inlet manifold Injectors
An exhaust gas oxygen sensor fitted to a vehicle engine pipe
Exhaust emission controls are designed to reduce the amount of harmful gases released through the exhaust system into the atmosphere. It is important that exhaust system components are regularly inspected, tested and serviced as necessary to ensure that emissions are kept to a minimum and maximum engine performance is maintained.
Exhaust Gas Oxygen Sensor
The exhaust gas oxygen sensor (EGO) forms part of the electrical circuit for electronic fuel injected vehicles, where actions taking place in the combustion chamber are assessed by the analysis of oxygen in the exhaust gases.
The amount of residual oxygen in the exhaust gas is used as an indirect measurement of air/fuel ratio. The signal produced by the EGO sensor enables the electronic control unit to accurately vary the amount of fuel being injected into the engine to obtain the most complete combustion.
Complete combustion normally occurs at air/fuel ratio of 14.7:1 (this is referred to as stoichiometric ratio).
An EGO sensor is often referred to as a Lambda sensor. An EGO sensor operates on the principle that some materials, under certain conditions attract negatively charged electrons to their surface.
The EGO sensor is usually mounted in the exhaust manifold or close to it in the engine pipe as it operates more efficiently at high temperatures.
EXHAUST EMISSION CONTROL SYSTEMS
Varies the amount of fuel injected Dedicated earth return Catalytic converter Resonator Exhaust gas oxygen sensor Rear muffler
The current from an EGO sensor is very low and must be amplified within the electronic control unit before it can be used. A dedicated earth return lead is also often installed to ensure the signal has an accurate ground reference.
EGO sensor output does not reflect oxygen content very well when its operating temperature is below 300°C. Normal operating temperature is 350°C and above. When cold, EGO switching speed is slow and the voltage difference between rich and lean is not very great. So the electronic control unit will disregard EGO outputs until the sensor has reached its operating temperature.
This may mean several kilometres of driving before the air/fuel ratio can be controlled more accurately and hence some fuel may be wasted and emissions may be higher during this period. The EGO sensor may also cool down during extended idle and again become ineffective.
Heated Exhaust Gas Oxygen Sensor
In an effort to speed up EGO warm up, many vehicles have a heater built into the sensor. This reduces warm up time significantly and maintains EGO sensor operating temperature during idling.
Operating temperature Exhaust gas Bushing (electrode) Thermal support (lead wire insulation)
Lead wire Spring Exhaust manifold Zirconia pipe Louvre Reduces warm up time Sensor
housing Protective ceramic tube
Connection cable
Protective
tube with slots Active sensor ceramic
Contact
element Protective sleeve Heater
Clamp terminals for heater
Exhaust Gas Recirculating System (EGR)
The EGR system is designed to reduce the amount of Oxides of nitrogen (NOx) created by the engine during operating periods that that result in high combustion temperatures. NOx is created when combustion temperatures exceed about 1350deg Celsius.
The EGR valve is designed to recirculate a small amount of exhaust gases back into the inlet manifold during these peak temperature periods.
This reduces the overall amount of air/fuel mixture which can enter the combustion chambers. As the recirculated gases are incombustible they absorb heat rather than create heat. Together these effects reduce the peak temperatures.
In older vehicles equipped with a carburettor the EGR is controlled by a vacuum operated PVS valve.
In electronic fuel injected vehicles the EGR is controlled by the electronic control unit (ECU) that monitors information about the engine received from sensors positioned around the vehicle. These sensors monitor water temperature, speed, and throttle position as well as exhaust temperatures.
Generally speaking the EGR flow should match the following conditions:
High EGR flow is necessary during cruise and mid range acceleration when combustion temperatures are normally high.
Low EGR flow is needed during low speed and light acceleration.
No EGR flow should occur when EGR operation could affect engine drivability or efficiency i.e. engine warm-up, idle, full throttle etc.
The two main components on a typical EGR system are the control valve which controls the amount of exhaust gases flow to the intake system, and the vacuum modulator which precisely regulates the vacuum strength required to operate the control valve. Exhaust manifold Inlet manifold Combustion chamber Solenoid Valve Throttle body Injector Modulator valve EGR control valve ECU Input Sensors A mounted EGR valve
As exhaust backpressure is proportional to engine load the EGR vacuum modulator uses this principle to precisely control the amount of vacuum to the EGR valve. The vacuum modulator operation is assisted by the ECU which is receiving and monitoring data from various sensors regarding engine operating conditions.
EGR Control Valve
The EGR control valve is used to regulate exhaust gas flow to the intake manifold by means of a pintle valve attached to the EGR valve diaphragm.
EGR Modulator Valve
The EGR modulator valve controls the EGR flow in relation to engine load conditions. Under high engine loads the EGR flow rate increases, while under lower engine loads the EGR flow rate decreases. The EGR modulator uses a combination of manifold vacuum and exhaust back pressure to determine the level of EGR flow required.
EGR Solenoid Valve
The EGR solenoid valve is used to prevent EGR valve operation during engine operating conditions where EGR operation can adversely affect engine performance (for examples engine temperature is low or high engine RPM required).
Where the ECU determines that the EGR operation is not required, the ECU signals this information to the EGR solenoid which closes off the vacuum supply to the EGR valve.
Ported Vacuum Switch (Coolant Controlled Valve) The ported vacuum switch (PVS) is generally a three port type valve which is usually installed into the thermostat housing. The base of the PVS is in constant contact with the coolant.
Three ports are housed on the body of the valve. The top port is the atmospheric port and is open to the atmosphere. The middle port is the inlet vacuum port and is connected to the emission control device (usually EGR valve). The bottom port is the inlet manifold port.
When the engine reaches operating temperature, the coolant melts the wax element at the base of the valve. This causes the wax element to expand and to lift the valve plunger and ball, thereby compressing the return spring.
The ball closes off the atmospheric port and opens the inlet vacuum port. This allows the engine vacuum from the inlet manifold port to act on the EGR valve through the inlet
Solenoid valve vacuum ports power supply
Base in coolant
Melts wax element
A catalytic converter
Catalytic Converter
Catalytic converters are normally located close to the exhaust manifold in the engine pipe.
The catalytic converter is designed to convert harmful pollutants such as hydrocarbons, carbon monoxide and oxides of nitrogen which are all found in exhaust emissions into harmless gases such as nitrogen, carbon dioxide and water.
Catalytic converters were made compulsory for all new cars manufactured after January 1986 with the introduction of ADR 37.
Catalytic converters contain a ceramic honey comb shaped insert that is coated with precious or noble metals, such as platinum, palladium and rhodium.
The multi channelled structure of this honey comb design has an extremely high surface area of up to 40 cells per square centimetre.
As the hot exhaust gases (600-900˚C) pass through the honey comb insert, a chemical reaction takes place and the conversion of gases is achieved.
The catalytic converter entry and exit pipes are in line with each other and normally have flanges on each end so that removal and replacement can be performed quickly and easily.
The catalytic converter’s outer skin is doubled to maintain the optimum working temperature.
Lead in fuel can cause a severe deactivation at levels above 5mg per litre of fuel. It is essential that vehicles equipped with catalytic converters always operate on unleaded fuel.
If temperatures exceeding 1400ºC are achieved the catalyst substrates within the catalytic converter will melt. Catalyst melting is normally accompanied by loss of power due to excessive exhaust back pressure.
High substrate temperatures are caused by malfunction of the ignition or fuel systems. Misfires at high speed may result in almost instantaneous melt of the catalyst substrates. A blocked catalytic converter restricts power, acceleration and overall performance. Before attempting to carry out any emission system repairs technicians must read the relevant workshop manual for the vehicle. Vehicles with engine management systems will typically have inbuilt fault finding capabilities that generate codes to identify individual faults.
When using a gas analyser on a vehicle which has a catalytic converter fitted emission readings at the tailpipe will differ to those taking at the front of the catalytic converter.
A catalytic converter fitted to a vehicle Harmful gases Chemical reaction Entry and exit pipes Unleaded fuel Misfires
An Exhaust Gas Analyser
Note for vehicles fitted with catalytic converters the HC reading is no longer an effective tool to indicate misfire on a lean running engine.
Each of the following components will affect the extent of exhaust emissions: Carburettor idle mixture adjustment (Older carburettor models)
Exhaust gas oxygen sensor Heated exhaust gas oxygen sensor Exhaust gas recirculation valve Air pump
Catalytic converter
Intake air temperature control valve Exhaust Gas Analyser
The exhaust gas analyser measures the amount of (5 gases) hydrocarbons, carbon monoxide, carbon dioxide, NOx and oxygen that is being emitted from a vehicle.
This measurement is expressed in percentage terms or parts per million. Each vehicle will have a recommended emission percentage level. During an exhaust emission test an exhaust gas analyser probe is inserted into the exhaust tail pipe and an emission reading is registered and displayed on the exhaust gas analyser screen. Using an exhaust gas analyser:
1 Warm-up the engine to normal operating temperature. Switch off accessories such as air conditioning.
2 Insert the sampling probe into the exhaust pipe. 3 Run the engine at idle with the air cleaner
installed. Note the HC and CO readings.
4 Increase engine speed to the speed specified by the manufacturer. Note the HC and CO readings. 5 Return the engine to idle and note the HC and CO
readings again.
6 Compare readings to manufacturer’s specifications. Exhaust emission control devices Exhaust Emissions HC and CO
CO-Carbon Monoxide
Carbon monoxide is a tasteless, odourless and poisonous gas that forms during the combustion process due to incomplete combustion, resulting from a lack of oxygen or too much fuel. Carbon monoxide reduces the flow of oxygen in the bloodstream and is particularly dangerous to people with heart disease.
Abnormal CO Readings
An exhaust gas analyser measures CO levels in percentage volume. The level of CO in the exhaust gas is related to the air-fuel mixture. A high CO reading indicates an over-rich mixture (too much fuel compared to air). A low CO reading indicates a lean mixture (not enough fuel compared to air).
Composition
COis made up of one carbon atom and one oxygen atom. Typical causes of high CO readings include:
1 Fuel system faults – faulty injector, computer fault. 2 A dirty air cleaner or restricted air intake.
3 Incorrect ignition timing – timing too advanced or insufficient vacuum on the distributor vacuum advance unit.
4 Engine oil fuming due to engine blow-by, worn rings, burnt valve, incorrect valve clearance, defective valve springs, blown head gasket or low engine compression. 5 Malfunctioning air pump or system.
Impact on vehicle performance
A vehicle that is producing high CO will not be operating at the ideal stoichiometric level. Engines with high CO will have poor fuel economy and will have lower power output than specified.
The underlying cause if ignored may result in engine damage. CO2-Carbon Dioxide
Carbon Dioxide does not directly impair human health, however it is a green house gas that traps the Earths heat and contributes to the potential for global warming. Like CO, Carbon Dioxide is a by product of combustion. Ideal combustion produces large amounts of CO2 and water vapour.
Composition
CO2 is made up of one carbon atom and two oxygen atoms.
Abnormal CO2 readings
The CO2 reading provides an indication of combustion efficiency that peaks at or near the
stoichiometric air-fuel ratios, and decreases with a lean or rich air-fuel ratio. Consequently, the higher the carbon dioxide reading the more efficiently the engine is operating. Ideal combustion should produced CO2 of close to 15%.
Percentage volume
Typical causes for low CO2 readings
1. Fuel mixture is too rich. 2. Fuel mixture is too lean. 3. Exhaust system leaks. Impact on vehicle performance
A vehicle that is producing low CO2 will not be operating at the optimum level.
Incomplete combustion will reduce engine power and will result in poor fuel economy. The underlying cause if ignored by result engine damage.
HC- Hydrocarbons
Hydrocarbons are made up of hydrogen and carbon elements. These elements are burned in combustion with oxygen during combustion, but all the fuel may not be consumed during this process. This residue comes out the exhaust pipe as hydrocarbons.
Hydrocarbons react in the presence of nitrogen oxides and sunlight to form ground-level ozone, a major component of smog. Ozone irritates the eyes, damages the lungs, and aggravates respiratory problems.
Abnormal HC Readings
An exhaust gas analyser measures HC levels in parts per million (PPM) by volume. A high HC level indicates that there is excessive unburnt fuel in the exhaust. Main causes are ignition faults or incomplete combustion.
Typical causes of high HC readings include:
1 Incorrect ignition timing – distributor, computer or incorrect timing adjustment. 2 Ignition system faults that cause misfire – fouled spark plug, incorrect plug type,
cracked distributor cap, defective spark plug HT leads or breaker points. 3 Excessively rich or lean air-fuel mixture – carburettor or fuel injection fault. 4 Engine oil fuming due to blow-by, worn rings, burnt valve, valve clearance,
defective valve springs, blown head gasket or low engine compression.
5 Leaking vacuum hoses, gaskets, faulty positive crankcase ventilation or evaporative control system.
Impact on vehicle performance
A vehicle that is producing high HC will not be operating at the ideal stoichiometric level. High HO will result in poor fuel economy and will likely reduce engine power. The underlying cause if ignored may result engine damage.
NOx – Oxides of Nitrogen
Oxides of Nitrogen are the result of high combustion temperatures. Too little fuel in the Parts per million Rich or lean air/fuel mixture Smog
Composition
NOx is made up of nitrogen and oxygen atoms.
Typical causes of highNOx readings include: 1. Fouled exhaust gas recirculation (EGR) valve 2. EGR system passages clogged
3. Incorrect spark plugs (those with elevated heat range) 4. Malfunctioning catalytic converter
5. Lean fuel mixture (too much air) Impact on vehicle performance
A vehicle that is producing high NOxwill not be operating at the ideal stoichiometric level and it is symptom of a lean mixture. High NOx will reduce engine power. The underlying cause if ignored will result in engine damage.
O2 – Oxygen
The oxygen level is used as an indication of how near the engine is running to the ideal stoichiometric air-fuel ratio. With leaner air/fuel mixtures the O2 level increases and with richer mixtures the O2 decreases. Usually if the O2 readings increase the CO decreases and vice versa.
Composition
O2 is made up of two oxygen atoms.
Impact on vehicle performance
A vehicle that is producing high O2 will not be operating at the ideal stoichiometric level and it is symptom of a lean mixture. Engines that have high O2 will have lower power output than specified. The underlying cause if ignored will result in engine damage. Particulates
Particulates, also known as soot, is visible as black smoke that is emitted from the exhaust tail pipe when the engine is running very rich, it is not measured by a gas analyser. This soot has been linked to lung and heart disease. Modern EFI vehicles are equipped with sensors that control the enrichment system to ensure that the mixture is ideally set.
Composition
Typically made up of a variety of atoms, including Sulphur, Carbon, Nitrogen, and Oxygen.
Impact on vehicle performance
A vehicle that is producing particulates will have reduced engine power and poor fuel economy. The underlying cause if ignored will result in engine damage.
Diesel Particulate Filters (DPF)
In response to strict Australian emission standards manufacturers of diesel vehicles have introduced diesel particulate filters.
These filters are an exhaust gas filter on diesel engines that capture the fine soot particles (a by-product of the combustion process in a diesel engine).
The most common type of DPF is an oxidising catalytic converter fitted close to the engine in the exhaust system where exhaust gas temperature is at its highest and passive regeneration is more likely to be successful.
A particular feature of these systems is that they require a special clean from time to time depending on the driving distances and engine temperatures of the vehicle.
During the cleaning process a ‘Burn Off” or regeneration is carried out – the collected soot particles within the filter are burnt off under high temperatures to leave only an ash residue. Failure to carry out the regeneration of the DPF may leave the vehicle inoperable as the exhaust system becomes blocked.
When the particulate filter requires regeneration a warning light will show on the dash panel.
Regeneration is designed to take place during high speed long distance trips where the exhaust reaches high temperatures. These consistent high temperatures prevent soot build up within the particulate filter.
For vehicles that are mainly used for shorter journeys the ECU will trigger regeneration when the DPF has reached around 45% capacity. At this stage the ECU alters the fuel injection cycle to increase exhaust temperature.
If the journey is too short and regeneration can’t be completed then a warning light will be illuminated on the dash panel to caution the driver that the filter is partially blocked. The process can be completed by driving at a speed greater than 70 km/h for a further 10mins.
If this process is not completed and soot levels continue rise to around 70% then the vehicle performance will reduce and the engine will switch automatically to restrictive mode to prevent further engine damage.
DPF additives
Some newer models have a separate tank for an additive fluid containing Cerium (III) oxide. Cerium ignites at a far lower temperature and adheres to the soot particles meaning regeneration can occur at lower temperatures.
The additive is stored in a separate tank next to the fuel tank fill points. The additive is automatically mixed with fuel whenever you fill up. Only very small quantities are used.
Note: For more information regarding the additive consult the owner’s manual or workshop manual.
Supplementary Catalytic Systems (SCR)
SCR is an emission reducing technology for diesel engine vehicles where a liquid agent is injected into a catalyst in the exhaust system after the particulate filter. The liquid is usually automotive-grade urea, otherwise known as diesel exhaust fluid (DEF). The DEF sets off a chemical reaction which converts nitrogen oxides into nitrogen, water and tiny amounts of carbon dioxide (CO2). SCR technology is a very cost effective method of reducing diesel engine emissions.
All new diesel truck engines must meet stringent emissions standards, reducing particulate matter (PM) and nitrogen oxides (NOx) to near zero levels. SCR can reduce NOx emissions up to 90% and at the same time reducing HC and CO emissions by 50-90%, and PM emissions by 30-50%. SCR systems if combined with a diesel particulate filter can achieve even greater emission reductions for particulate matter.
The air intake supplies and controls the amount of air required by the engine. The system consists of: Components include: Air filter Throttle body Intake manifold Inlet ducting
Throttle position sensor Mass air flow sensor
Intake air temperature sensor
Air filters
The air that enters the engine must be free of dust. Most air filters use a paper element inside a metal, or plastic, container.
The element should be replaced regularly, as the large amount of air used by an engine, means that considerable dust is removed.
Air filter housing Mass Air flow sensor Intake manifold Throttle body Throttle position sensor Ducting Crankcase ventilation hose Paper element
Throttle Body
The throttle body controls the amount of air admitted into the engine by restricting the intake venturi by means of a throttle plate. Opening the throttle plate increases the air flow, thereby increasing engine speed. Throttle plate movement is operated by a cable connected to an eccentric cam. A throttle position sensor is located on the throttle plate shaft and monitors the throttle position and provides an electrical signal to the ECU.
The throttle body housing is an aluminium casting with several air passages and a throttle plate. Located on the side of the throttle body casing is a throttle stop screw that prevents the throttle plate from contacting the bore and sticking closed.
Inlet manifold
Inlet manifolds are usually manufactured from aluminium or cast iron. The function of the manifold is to:
Provide a path for the air-fuel mixture to the combustion chamber.
Prevent fuel from separating from the air-fuel mixture.
Evenly distribute the air–fuel mixture to each cylinder.
Help warm the air fuel mixture when the engine is cold.
Mass Air Flow Sensor
The mass air flow sensor measures the intake air volume and is located between the air filter and the inlet manifold. This is used by the control system to calculate the basic injection and ignition times.
The main types of air flow sensors are the Vane unit, heated resistor, Karmen Vortex and Manifold absolute pressure (MAP).
Intake air volume Aluminium or cast iron A throttle body Throttle plate control
An electronic air flow meter Inlet manifold
To intake manifold
To ECU
Manifold Absolute Pressure Sensor
The MAP sensor is used by the electronic control unit to determine the actual air pressure in the inlet manifold at any time of engine operation.
It also detects the ambient air pressure when power is applied prior to the engine being started to provide compensation for altitude and atmospheric conditions. It converts these pressure readings into a voltage or a frequency signal.
A reference voltage is supplied to the sensor from the ECU, and as manifold vacuum varies on the sensor, the electrical output varies from 0 to 5 volts. As manifold pressure increases, voltage output increases, as manifold pressure decreases, voltage output decreases.
This information is used as part of the calculations within the electronic control unit to determine the actual mass of air entering the engine.
This enables the electronic control unit to then calculate the correct amount of fuel for injection under any condition of engine operation.
MAP sensors rely on the change in capacitance when two capacitor plates are moved closer together or further apart, to vary capacitance and therefore the MAP input signal to the ECU.
Its construction consists basically of two metal coated flexible plates, which form the positive and negative plates of a capacitor.
An electrical lead is connected to each plate. The plates are separated by a hollow cylindrical insulating spacer, similar to a washer. This is then sealed to form a chamber.
This capsule is then placed inside a sealed container that is connected to the inlet manifold vacuum.
When manifold pressure is applied to the plates they deflect inwards, thus altering the capacitance between the plates.
Different manifold pressures will flex the plates by different amounts, thereby providing a different value of capacitance for each value of manifold pressure.
Air flow sensor electrical circuit Actual air pressure Metal coated flexible plates Manifold vacuum
From manifold Sealed housing Connecting fluid Film electrode Insulating washer shape spacer
Throttle position sensor
This variable capacitance does not provide a signal by itself and the MAP sensor must use other internal circuits to obtain a useful signal. It does this by the inclusion of a simple oscillator circuit. An oscillator is a circuit that generates an AC output from a DC input.
Idle Air Control Valve (IAC)
The idle air control valve is mounted on top of the throttle body housing and is designed to increase or decrease the amount of air that bypasses the throttle valve to maintain a smooth idle speed. The IAC is controlled directly by the ECU.
The ECU uses the IAC to control the idle speed as the engine progresses from cold starting through to normal engine operating temperatures.
If an additional load was placed on the engine, for example an air conditioning compressor is activated, the ECU will adjust the IAC to allow more air to enter the engine and thereby increase engine speed.
Throttle Position Sensor (TPS)
This type of sensor contains a potentiometer with a wiper or pointer that is rotated by the throttle butterfly shaft. The TPS is positioned onto the throttle body with one end of the throttle shaft entering the sensor.
The most commonly used TPS has a three wire external connection, one wire supplies the 5 volt reference voltage from the ECU, the second wire is the signal wire from the TPS to the ECU and the final wire in the TPS is the ground wire.
TPS signals the exact position of the throttle shaft to the ECU so the ECU can alter many different systems. The TPS does this by using a potentiometer type sensor that has a high resistant level and a low resistant level.
For example, when the throttle butterfly is in the closed position the signal being sent to the ECU would be approximately 1000 Ohms which would give a voltage reading of between 0.5 –0.85 volts. With the throttle butterfly at wide-open throttle the signal be sent would be approximately 4000 Ohms and a voltage reading of 4 – 4.5 volts approximately.
Through the signals sent by the throttle position sensor, the ECU can measure how fast the throttle is being opened and adjust the relative systems as necessary.
When the engine is accelerating quickly the engine requires a much richer air/fuel ratio as compared to when accelerating slowly due to the sudden intake of air. The throttle position sensor signals how fast and how far the throttle has opened to the ECU, which in turn adjusts the air/fuel ratio. This prevents damage caused by a ‘flat spot’ during engine performance.
DC input AC output
High and low resistance levels
Idle air control valve
Increase and decrease air flow Potentiometer Throttle position adjust air fuel ratio
Intake Air Temperature Sensor (IAT) The IAT sensor is commonly located within the inlet manifold or in the air cleaner element box.
The sensor consists of an external electrical connection to the ECU and a brass sensing bulb that is inserted into the inlet manifold.
The signal from the IAT is used during the start up of the engine, in colder ambient conditions and during periods of wide-open throttle.
As cold air is denser, more fuel must be added to keep the air/fuel ratio correct for satisfactory engine performance. When the IAT sensor senses colder conditions, it signals this information to the ECU, which in turn adjusts the air/fuel mixture to the correct stoichiometric ratio.
The Electronically Controlled Fuel Injection system (EFI) controls the quantity of fuel supplied and time of delivery, by processing signals from many engine sensors in a micro processor, called an ECU (electronic control unit). Typical input devices include throttle position, air flow, engine temperature, manifold pressure, crank angle sensor, air temperature, knock sensor.
The most common output devices are injectors, ignition system, emissions control and idle control. The quantity of fuel injected is governed by the injector opening frequency (determined by engine speed) and pulse width (determined by engine load and operating conditions) which allows fuel requirements to be met solely by injector control.
The EFI system consists of the following three subsystems. Intake Air System
Measures and controls the amount of air required by the engine. Fuel System
Supplies fuel to the engine and controls the required fuel pressure to maintain the correct amount of fuel injection to each cylinder.
Control System Controls spark timing.
Controls fuel injection volume and fuel injection timing. Controls emissions systems e.g. Air injection, EGR etc. Input and
output Signals
Subsystems
FUEL INJECTION SYSTEMS Colder conditions Adjusts air/fuel ratio Connector Boot Terminal Gasket Bulb Epoxy filler Shield Thermistor
Air injection systems are designed to introduce air into the exhaust system to assist in burning the gases produced by the engine. Air is injected into the exhaust system at one of several locations including the cylinder head, exhaust manifold or directly into the catalytic converter.
Air is drawn in by an air pump or a reed valve. The air pump is operated either by a drive belt on the front of the engine or by a small electric motor. The reed valves work by sensing the drop in manifold vacuum produced by an exhaust valve closing. Each time the drop in vacuum occurs air is drawn into the exhaust system.
The air pump is designed to inject air into the exhaust port to aid the complete combustion of the air fuel mixture thereby reducing the levels of hydrocarbon and carbon monoxide emissions.
Reed Valve Air Injection System
The reed valve air injection system uses check valves, supply hoses and injection nozzles to reduce the levels of hydrocarbon and carbon monoxide emissions.
During the combustion process the engine exhaust pulsates, this creates a vacuum in the exhaust manifold.
This vacuum opens a reed valve that allows air to be drawn from the air cleaner through the air supply hoses to the injection nozzles mounted inside the exhaust manifold.
However when the engine speed is increased the pressure within the exhaust system exceeds the air injection system pressure and closes the reed valve to prevent exhaust gases from entering the air cleaner.
Throttle Damper (Anti Stall Dashpot)
A throttle damper allows the throttle valve to close slowly on deceleration, this prevents excessive hydrocarbon emissions.
A manifold vacuum that is higher than the idle vacuum is suddenly introduced when the throttle valve is snapped shut. This can cause excessive engine emissions and in some cases the vehicle to stall. Excessive emissions Injects air Exhaust pulsates
An air injection air pump
AIR INJECTION SYSTEMS
The throttle damper or anti-stall is commonly found on vehicles with automatic transmissions. The damper allows the automatic transmission torque converter enough time to release and the transmission enough time to dissipate line pressure.
Anti-after burn Valve
On deceleration the anti-after burn valve is designed to prevent back-firing through the exhaust system.
When the throttle is released the anti-after burn valve opens and allows additional air into the inlet manifold. This assists in reducing carbon monoxide and hydrocarbon emissions.
SECTION OVERVIEW
Emission standards have been introduced to reduce the levels of harmful vehicle exhaust emissions to the atmosphere.
Emission control systems are fitted to vehicles to reduce the levels of harmful exhaust emissions to the atmosphere.
Evaporative systems typically include the following components: Fuel tank and fuel lines
Fuel cap Roll over valve Carbon canister
Purge control valve/solenoid
The positive crankcase ventilation system is designed to release pressure and vapours from the crankcase by directing them back into the inlet manifold where they can be burnt in the cylinder.
An exhaust gas analyser is a diagnostic tool that is used to measure exhaust emissions. Key Points
Dissipate line pressure
Prevent back firing
REVIEW QUESTIONS ONE
1. Name three harmful gases that may be emitted from exhaust systems.
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
2. List two harmful effects that NOx has on the environment.
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
3. List three harmful effects that HC has on people.
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
4. Provide two reasons why it is important that the ozone layer is protected.
_________________________________________________________________ _________________________________________________________________
5. Name the current European Emissions Standard
_________________________________________________________________
6. What is the purpose of ADR37?
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________________________________________________________
7. Explain why it is important to reduce greenhouse gas emissions.
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
8. List five components designed to prevent fuel vapours from evaporating into the atmosphere.
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
9. What is the function of the rollover valve?
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
10. What is the function of the charcoal canister?
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________________________________________________________
11. What is the main function of a positive crankcase ventilation system?
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________________________________________________________
12. List three disadvantages that can be associated with using petrol as a fuel.
1 __________________________________________________________ 2 __________________________________________________________ 3 __________________________________________________________
13. Provide an advantage and a disadvantage associated with bio-diesel.
Advantage: ____________________________________________________ ________________________________________________________________ ________________________________________________________________ Disadvantage: ____________________________________________________ ________________________________________________________________ ________________________________________________________________
14. Provide three reasons why the roads are busier today than in past generations.
1 __________________________________________________________ 2 __________________________________________________________ 3 __________________________________________________________
15. Provide two advantages and two disadvantages that can be associated with electric fuelled vehicles.
Advantages: ______________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ Disadvantages: ______________________________________________ ________________________________________________________________ ________________________________________________________________
16. List three vehicle performance problems that may be created by excessive NOx. _________________________________________________________________ _________________________________________________________________ _________________________________________________________________
17. List two typical causes of high CO readings.
_________________________________________________________________ _________________________________________________________________
18. List three typical causes of high HC readings.
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________________________________________________________
19. Why is the O2 reading useful when diagnosing engine condition?
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
20. List the five gases that can be measured by an exhaust gas analyser
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
21. Complete the following sentence.
An EGO ________________ operates on the principle that some materials, under certain conditions attract __________________ charged ____________________ to their surface. The _____________ sensor is usually mounted in the exhaust __________________ or close to it in the engine _________________ because it operates more ___________________ at _______________ temperatures.
22. How does an Exhaust gas recirculation system reduce NOx emissions?
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________________________________________________________
23. Explain in your own words how a catalytic converter operates.
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________________________________________________________
24. What is the main difference between an EGO and a HEGO?
_________________________________________________________________ _________________________________________________________________ _________________________________________________________________
Appropriate service methods and correct repair procedures are essential for safe, reliable operation of all motor vehicles as well as the personal safety of the individual carrying out the work. The following list contains some general warnings that should be followed when working on a vehicle.
WARNING
Wear safety glasses for eye protection, where appropriate.
Use safety stands whenever a procedure requires you to be under the vehicle. Ensure that the ignition switch is always in the off position, unless otherwise
required by the procedure.
Set the hand brake when working on the vehicle.
Operate the engine only in a well-ventilated area to avoid the danger of carbon monoxide inhalation.
To prevent serious burns, avoid contact with hot metal parts such as the radiator, exhaust manifold, tail pipe, catalytic converter and muffler.
Do not smoke while working on a vehicle.
To avoid injury, always remove rings, watches, loose hanging jewellery, and loose clothing before beginning to work on a vehicle. Tie long hair behind the head.
Keep hands and other objects clear of the radiator fan blades. Electric cooling fans can start to operate at any time by an increase in temperature.
Avoid contact with battery acid. Do not smoke or have any flame, or sparks near a battery while it is being charged or used. Hydrogen gas emitted may explode.
Avoid contacting the eyes or skin with hot gear oil or cleaning fluid. Immediately seek medical advice if these fluids are swallowed.
Do not use petrol or highly flammable spirits when cleaning parts.
All general health and safety practices should be observed. Seek additional advice if necessary.
Use a heat shield when welding to prevent heat damage to other components. Take care when working with rusty components as cuts can lead to blood
poisoning.
OH&S requirements, including individual State/Territory regulatory requirements and personal protection needs are observed throughout the work.
National Environment Protection Measure for Diesel Vehicles (Guidelines) is sourced and observed throughout the work as applicable to tasks.
Caution
Modern vehicles have electronic components that will be damaged if 12V positive power is directly applied.
Ensure all electrical systems are switched off before disconnecting or reconnecting the vehicle battery.
Disconnect both battery leads before electric welding is commenced to prevent damage to electrical components.
Very Important Safety Points
SAFETY WHEN SERVICING VEHICLES
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