Emission Control - Land Rover V8
Engine design has evolved in order to minimize the emission of harmful by-products. Emission control Systems are fitted to Land Rover vehicles which are designed to maintain the emission levels within the legal limits pertaining for the specified market.
Despite the utilization of specialized emission control equipment, it is still necessary to ensure that the engine is correctly maintained and is in good mechanical order so that it operates at its optimal condition. In particular, ignition timing has an effect on the production of HC and NO2 emissions, with the harmful emissions rising as the ignition timing is advanced.
! CAUTION: In many countries it is against the law for a vehicle owner or an unauthorized dealer to modify or tamper with emission control equipment. In some cases, the vehicle owner and/or the dealer may even be liable for prosecution.
The engine management ECM is fundamental for controlling the emission control systems. In addition to controlling normal operation, the system complies with On Board Diagnostic (OBD) system strategies. The system monitors and reports on faults detected with ignition, fuelling and exhaust systems which cause an excessive increase in tailpipe emissions. This includes component failures, engine misfires, catalyst damage, catalyst efficiency, fuel evaporative loss and exhaust leaks.
When an emission relevant fault is determined, the fault condition is stored in the ECM memory. For NAS vehicles, the MIL warning lamp on the instrument pack will be illuminated when the fault is confirmed. Confirmation of a fault condition occurs if the fault is found to be present during the driving cycle subsequent to the one when the fault was first detected. Refer to Engine Management System. Description and Operation
Three main types of supplementary control system are employed to reduce harmful emissions released into the atmosphere from the vehicle. These are:
- Crankcase emission control - also known as blow-by gas emissions from the engine crankcase.
- Exhaust emission control - to limit the undesirable by-products of combustion.
- Fuel vapor evaporative loss control - to restrict the emission of fuel through evaporation from the fuel system.
Crankcase ventilation system
The concentration of hydrocarbons in the crankcase of an engine is much greater than that in the vehicle's exhaust system. In order to prevent the emission of these hydrocarbons into the atmosphere, crankcase emission control systems are employed and are a standard legal requirement.
The crankcase ventilation system is an integral part of the air supply to the engine combustion chambers and it is often overlooked when diagnosing problems associated with engine performance. A blocked ventilation pipe, filter or excessive air leak into the inlet system through a damaged pipe or leaking gasket can affect the air:fuel mixture, performance and economy of the engine. Periodically check the ventilation hoses are not cracked and that they are securely fitted to form airtight connections at their relevant ports.
The purpose of the crankcase ventilation system is to ensure that any noxious gas generated in the engine crankcase is rendered harmless by burning them in the combustion chambers. Burning the crankcase vapours in a controlled manner decreases the HC pollutants that could be emitted and helps to prevent the development of sludge in the engine oil as well as increasing fuel economy.
When the engine is running in cruise conditions, or at idle, manifold pressure is low and the majority of gasses are drawn into the inlet manifold through an oil/vapor separator (1), located in the RH rocker cover. At the same time, filtered air is drawn from the throttle body (3) into the engine via the LH rocker cover (2). The oil/vapor separator serves to prevent oil mist being drawn into the engine.
During periods of driving at Wide Open Throttle (WOT), pressure at either side of the throttle disc equalizes (manifold depression collapses). The larger ventilation opening (3), positioned in the fast moving stream of intake air, now offers more 'pull' than the small opening (1) in the RH rocker cover, and the flow of ventilation reverses. Gases are drawn from the LH rocker cover into the throttle body (3).
Crankcase Ventilation System - From 99MY:
A spiral oil separator is located in the stub pipe to the ventilation hose on the right hand cylinder rocker cover, where oil is separated and returned to the cylinder head. The rubber ventilation hose from the right hand rocker cover is routed to a port on the right hand side of the inlet manifold plenum chamber, where the returned gases mix with the fresh inlet air passing through the throttle butterfly valve. The stub pipe on the left hand rocker cover does not contain an oil separator, and the ventilation hose is routed to the throttle body housing at the air inlet side of the butterfly valve. The ventilation hoses are attached to the stub pipe by metal band clamps.
Oil laden noxious gas in the engine crankcase is drawn through the spiral oil separator. The mass of fresh air which is drawn in from the atmospheric side of the throttle butterfly to mix with the returned crankcase gas depends on the throttle position and the engine speed.
Exhaust emission control.
The fuel injection system provides accurately metered quantities of fuel to the combustion chambers to ensure the most efficient air to fuel ratio under all operating conditions. A further improvement to combustion is made by measuring the oxygen content of the exhaust gases to enable the quantity of fuel injected to be varied in accordance with the prevailing engine operation and ambient conditions; any unsatisfactory composition of the exhaust gas is then corrected by adjustments made to the fuelling by the ECM.
The main components of the exhaust emission system are two catalytic converters which are an integral part of the front exhaust pipe assembly. The catalytic converters are included in the system to reduce the emission, to atmosphere, of carbon monoxide (CO), oxides of nitrogen (NOx), and hydrocarbons (HC). The active constituents of the converters are platinum, palladium and rhodium. The correct functioning of the converters is dependent upon close control of the oxygen concentration in the exhaust gas entering the catalysts.
The basic control loop comprises the engine (controlled system), the heated oxygen sensors (measuring elements), the engine management ECM (control) and the injectors and ignition (actuators). Although other factors also influence the calculations of the ECM, such as air flow, air intake temperature and throttle position. Additionally, special driving conditions are compensated for such as starting, acceleration and full load. Refer to Engine Management System. Description and Operation
The reliability of the ignition system is critical for efficient catalytic converter operation, since misfiring will lead to irreparable damage of the catalytic converter due to the overheating that occurs when unburned combustion gases are burnt inside it.
! CAUTION: If the engine is misfiring, it should be shut down immediately and the cause rectified. Failure to do so will result in irreparable damage to the catalytic converter.
! CAUTION: Ensure the exhaust system is free from leaks. Exhaust leaks upstream of the catalytic converter could cause internal damage to the catalytic converter.
! CAUTION: Serious damage to the engine may occur if a lower octane number fuel than that which is recommended is used.
! CAUTION: Only unleaded fuel must be used on vehicles fitted with catalytic converters; serious damage to the catalytic converter will occur if leaded fuel is used. A reminder label is adhered to the inside of the fuel filler flap. As a further safeguard, the filler neck is designed to accommodate only unleaded fuel pump nozzles.
The oxygen content of the exhaust gas is signalled to the Engine Control Module (ECM) by two Heated Oxygen Sensors (HO2S) located in the exhaust front pipes, upstream of each catalytic converter. The ECM can then make an appropriate adjustment to the fuel supply to correct the composition of the exhaust gases.
North American Specification (NAS) vehicles have additional Heated Oxygen Sensors, positioned downstream of each catalytic converter. The ECM uses the signals from these sensors to determine whether the catalysts are working efficiently.
HO2S Sensors And Exhaust System - Up To 99MY:
Detail of front pipe showing location of oxygen sensors. Only NAS vehicles have four sensors, Rest of World vehicles have two sensors, one mounted upstream (towards the exhaust manifold) of each catalytic converter.
HO2S Sensors And Exhaust System - From 99MY:
The oxygen content of the exhaust gas is monitored by heated oxygen (HO2S) sensors using either a four sensor (NAS only) or two sensor setup. Signals from the heated oxygen sensors are input to the engine management ECM which correspond to the level of oxygen detected in the exhaust gas. From ECM analysis of the data, necessary changes to the air:fuel mixture and ignition timing can be made to bring the emission levels back within acceptable limits under all operating conditions.
NOTE: Some markets do not legislate for closed loop fuelling control and in this instance no heated oxygen sensors will be fitted to the exhaust system.
Changes to the air:fuel ratio are needed when the engine is operating under particular conditions such as cold starting, idle, cruise, full throttle or altitude. In order to maintain an optimum air:fuel ratio for differing conditions, the engine management control system uses sensors to determine data which enable it to select the ideal ratio. Improved fuel economy can be arranged by increasing the quantity of air to fuel to create a lean mixture during part-throttle conditions. Improved performance can be established by supplying a higher proportion of fuel to create a rich mixture during idle and full-throttle operation.
The nominal voltage of the heated oxygen sensors at the stoichiometric point is 450 to 500 mV. This voltage decreases to between 100 and 500 mV if there is an increase in oxygen content. The voltage increases to between 500 and 1000 mV if there is a decrease in oxygen content, signifying a rich mixture.
Diagnosis of electrical faults is continuously monitored for both the pre-catalytic converter sensors and the post-catalytic converter sensors (NAS only). This is achieved by checking the signal against maximum and minimum thresholds for open and short circuit conditions. For NAS vehicles, if the pre- and post-catalytic sensors are inadvertently transposed, the lambda signals will go to maximum but opposite extremes and the system will automatically revert to open loop fuelling. The additional sensors for NAS vehicles provide mandatory monitoring of catalyst conversion efficiency and long term fuelling adaptations.
Failure of the closed loop control of the exhaust emission system may be attributable to one of the failure modes indicated below:
- Mechanical fitting and integrity of the sensor.
- Sensor open circuit/disconnected.
- Short circuit to vehicle supply or ground.
- Lambda ratio outside operating band.
- Crossed sensors.
- Contamination from leaded fuel or other sources.
- Change in sensor characteristic.
- Harness damage.
- Air leak into exhaust system (cracked pipe/weld or loose fixings).
System failure will be indicated by the following symptoms:
- MIL light on (NAS only).
- Default to open-loop fuelling for the defective cylinder bank.
- If sensors are crossed, engine will run normally after initial start and then become progressively unstable with one bank going to its maximum rich clamp and the other bank going to its maximum lean clamp - the system will then revert to open-loop fuelling.
- High CO reading.
- Strong smell of H2S (rotten eggs) till default condition.
- Excessive emissions. Refer to Engine Management System. Description and Operation
Evaporative emission control system - pre advanced EVAPS.
The system is designed to prevent harmful fuel vapor escaping to the atmosphere. The system comprises a vapor separator (C) and a two way valve (D), both located on the fuel filler neck (A), an Evaporative Emissions (EVAP) canister and an EVAP canister purge valve.
During conditions of high ambient temperatures, fuel in the tank vaporizes, and pressure rises. Fuel vapor enters the vapor separator and any liquid fuel runs back to the tank. Three roll over valves are fitted in the fuel tank vapor lines. These valves prevent liquid fuel entering the vapor separator if the vehicle rolls over. When pressure rises above 5 to 7 Kpa (0.7 to 1.0 labor/square in.), the two way valve opens and allows fuel vapor to flow to the EVAP canister where it is stored in the canister's activated charcoal element. When the correct engine operating conditions are met, the Engine Control Module (ECM) opens the EVAP canister purge valve and vapor is drawn from the canister, into the plenum chamber to be burned in the engine. Fresh air is drawn into the canister through a vent to take up the volume of displaced vapor. If the two way valve should fail, or the main vapor line becomes blocked, excess pressure is vented to atmosphere through a valve in the fuel filler cap. Similarly, the cap vent valve will open to prevent the tank collapsing if excessive vacuum is present.
When the temperature of fuel in the tank reduces, pressure also reduces and vapor must be drawn back into the tank. When tank pressure drops into vacuum, the two way valve opens, allowing fuel vapor to be drawn out of the EVAP canister into the fuel tank. Again, fresh air is drawn into the canister to take up the displaced volume.