Description

Engine Emission Control

CRANKCASE VENTILATION
The engine is ventilated through a part load and a full load breather. The part load breather is a flexible composite hose connected between the PCV (positive crankcase ventilation) valve mounted above the oil separator in the RH (right-hand) bank camshaft cover and the induction elbow.

SECONDARY AIR INJECTION
AIR (secondary air injection) is fitted to the vehicle to reduce exhaust emissions to meet European Union (EU) Stage 4 and Federal Petrol Emission standards. The AIR (secondary air injection) system comprises:
- AIR (secondary air injection) pump
- AIR (secondary air injection) valve
- Associated pipes
- AIR (secondary air injection) pressure sensor (NAS only)
The AIR (secondary air injection) pump is used to provide a supply of air into the exhaust manifolds during the cold start period of the engine. The AIR (secondary air injection) cycle lasts for up to 65 seconds. The hot unburnt fuel particles leaving the combustion chamber mix with the air injected into the exhaust manifolds and immediately combust.
This subsequent combustion of the unburnt and partially burnt CO (carbon monoxide) and HC (hydrocarbon) particles help to reduce the emission of these pollutants from the exhaust system. The additional heat generated in the exhaust manifold also provides rapid heating of the exhaust system catalytic converters. The additional oxygen which is delivered to the catalytic converters also generates an exothermic reaction which causes the catalytic converters to reach their optimum operating temperature and 'light off' quickly.
The catalytic converters only start to provide effective treatment of emission pollutants when they reach an operating temperature of approximately 250°C (482°F) and need to be between temperatures of 400°C (752°F) and 800°C (1472°F) for optimum efficiency. Consequently, the heat produced by the AIR (secondary air injection) 'afterburning' reduces the time delay before the catalysts reach an efficient operating temperature.

EGR SYSTEM
The EGR (exhaust gas recirculation) system comprises of an EGR (exhaust gas recirculation) valve and exhaust manifold to EGR (exhaust gas recirculation) valve tube. The EGR (exhaust gas recirculation) system allows a measured quantity of exhaust gas to be directed back to the intake manifold. The exhaust gas is introduced to the incoming charge air in the intake manifold, where it mixes with the air/fuel mixture and lowers the peak gas temperature, reducing NOX (oxides of nitrogen) exhaust emissions. The gas is drawn through the exhaust manifold to EGR (exhaust gas recirculation) valve tube from the exhaust to the inlet manifold through the EGR (exhaust gas recirculation) valve. The EGR (exhaust gas recirculation) valve is electrically operated and is controlled through an input from the
ECM (engine control module).
The ECM (engine control module) monitors the operation of the EGR (exhaust gas recirculation) system from inputs from the MAP (manifold absolute pressure) sensor and can detect high or low flow through the valve as a result of changes to the pressure readings.
High or low flow outside the expected range results in the setting of a DTC (diagnostic trouble code).
On vehicles without a supercharger the MAP (manifold absolute pressure) sensor is mounted on the rear of intake manifold. On vehicles with a supercharger the MAP (manifold absolute pressure) sensor is mounted on the rear of the throttle body elbow.)

POSITIVE CRANKCASE VENTILATION VALVE





The PCV (positive crankcase ventilation) valve is a spring loaded valve that opens when the engine is under full load. Once open the valve allows crankcase gasses to flow to the intake manifold. The PCV (positive crankcase ventilation) valve also prevents reverse flow into the crankcase.

SECONDARY AIR INJECTION PUMP





The AIR (secondary air injection) pump is fitted on rubber mountings to help prevent noise which is generated by AIR (secondary air injection) pump operation. The AIR (secondary air injection) pump is powered from the vehicle battery by a dedicated relay and supplies approximately 10 to 15 kg/hr (22 to 33 lb/hr) of air when the engine is at idle speed and the ambient temperature is below 20°C (68°F).
Air is drawn into the AIR (secondary air injection) pump through vents in its front cover and is then passed through a foam filter. The air is delivered to the exhaust manifold on each side of the engine through a combination of plastic pipes and stainless steel tubes.
One second after the AIR (secondary air injection) pump is energized, the ECM (engine control module) switches on the AIR (secondary air injection) switching valve, which opens to allow vacuum from the AIR (secondary air injection) vacuum reservoir to be applied to the vacuum operated AIR (secondary air injection) control valve. When the vacuum is applied to the AIR (secondary air injection) control valve, it opens to allow the air from the AIR (secondary air injection) pump through to the exhaust manifolds.
When the ECM (engine control module) switches off the AIR (secondary air injection) switching valve, the vacuum supply to the AIR (secondary air injection) control valve is cut-off and the valve closes to prevent further air being injected into the exhaust manifolds. With an approximate five second delay after as the AIR (secondary air injection) switching valve is closed, the ECM (engine control module) removes power from the AIR (secondary air injection) pump relay, and this in turn stops the AIR (secondary air injection) pump from operating.

SECONDARY AIR INJECTION SWITCHING VALVE





The ECM (engine control module) switches on the AIR (secondary air injection) switching valve with a one second delay after initiating AIR (secondary air injection) pump operation. When the AIR (secondary air injection) switching valve is open, a steady vacuum supply is allowed through to open the vacuum operated AIR (secondary air injection) control valve. When the ECM (engine control module) switches off the AIR (secondary air injection) switching valve, the valve closes and immediately shuts off the vacuum supply to the AIR (secondary air injection) control valve. The pump continues to operate for a further five seconds for system diagnostic purposes.
When the AIR (secondary air injection) switching valve is switched off, the vacuum supply line opens to atmosphere, and this causes the AIR (secondary air injection) switching valve to close automatically to prevent any further injection of air.

SECONDARY AIR INJECTION CONTROL VALVE





The injected air from the AIR (secondary air injection) pump is controlled by the AIR (secondary air injection) control valve. This allows the correct amount of air to be injected directly into the exhaust manifolds. The AIR (secondary air injection) control valve prevents exhaust gasses from blowing back into the AIR (secondary air injection) pump. Vacuum to the AIR (secondary air injection) switching valve is provided from the intake manifold vacuum by the AIR (secondary air injection) vacuum reservoir. A small bore vacuum hose provides the vacuum route between the AIR (secondary air injection) vacuum reservoir and AIR (secondary air injection) switching valve. A further small bore vacuum hose is used to connect the AIR (secondary air injection) switching valve to the
AIR (secondary air injection) control valve.
The AIR (secondary air injection) control valve is assisted in operation by a vacuum source from the AIR (secondary air injection) vacuum reservoir located in the right-hand side of the engine bay. This assistance allows the actuation of the AIR (secondary air injection) control valve independently from the intake manifold vacuum levels available.
When the pressure in the exhaust system is higher than in the AIR (secondary air injection) system, the AIR (secondary air injection) control valve closes the circuit, and this protects the AIR (secondary air injection) system from exhaust gasses blowing back into the AIR (secondary air injection) system.
Vacuum to the AIR (secondary air injection) switching valve is provided from the intake manifold vacuum by the AIR (secondary air injection) vacuum reservoir. A small bore vacuum hose provides the vacuum route between the AIR (secondary air injection) vacuum reservoir and AIR (secondary air injection) switching valve. A further small bore vacuum hose is used to connect the AIR (secondary air injection) switching valve to the AIR (secondary air injection) control valve.

SECONDARY AIR INJECTION RESERVOIR





The AIR (secondary air injection) vacuum reservoir is included in the vacuum supply line between the intake manifold and the AIR (secondary air injection) switching valve. The AIR (secondary air injection) vacuum reservoir contains a one-way valve to stop vacuum leaking back towards the intake manifold side.
The AIR (secondary air injection) vacuum reservoir holds a constant vacuum so that the AIR (secondary air injection) control valve opens as soon as the AIR (secondary air injection) switching valve is switched on.

SECONDARY AIR INJECTION PRESSURE SENSOR (NAS only)





The AIR (secondary air injection) system is monitored by measuring the system pressure by using the AIR (secondary air injection) pressure sensor at several instances during its cycle of operation.
The AIR (secondary air injection) system pressure is measured before operation of the AIR (secondary air injection) pump. The AIR (secondary air injection) pump is then switched on and with a one second delay, the AIR (secondary air injection) switching valve is opened. After a stabilizing period, the system pressure is measured again, this time by taking the average of a one second duration of readings, and normalizing for variations in battery voltage and atmospheric pressure. If the system pressure measured at this time has not risen enough with respect to the initial AIR (secondary air injection) pressure reading then a failure will be flagged.
A second pressure measurement is made after the requirement for AIR (secondary air injection) into the exhaust system has expired, but continuing on from the same period of AIR (secondary air injection) pump operation, i.e. the pump is left running, against a closed AIR (secondary air injection) switching valve. Again this pressure measurement is the average of a one second duration of readings normalized for variations in battery voltage and atmospheric pressure. If the system pressure measured at this time has not risen enough or has risen too much with respect to the system pressure during normal operation of AIR (secondary air injection) then a failure will be flagged.
A final pressure reading is taken after the AIR (secondary air injection) system has been switched off to ensure the system shuts down.

EGR VALVE





The EGR (exhaust gas recirculation)valve is a 4 pole 60 point stepper motor with an integral cooler unit which is mounted on the side of the induction elbow. The EGR (exhaust gas recirculation) valve receives four 12 Volt signals from the ECM (engine control module). The EGR (exhaust gas recirculation) valve is cooled by the return coolant flow from the electric throttle. The EGR (exhaust gas recirculation) valve is connected to the LH (left-hand) exhaust manifold via the gas transfer pipe.