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EMISSION CONTROL - V8 DESCRIPTION AND OPERATION 17-2-35 Failure of the closed loop control of the exhaust emission system may be attributable to one of the failure modes l Mechanical fitting & integrity of the sensor. l Sensor open circuit / disconnected. l Short circuit to vehicle supply or ground. l Lambda ratio outside operating band. l Crossed sensors. l Contamination from leaded fuel or other sources. l Change in sensor characteristic. l Harness damage. l Air leak into exhaust system (cracked pipe / weld or loose fixings). System failure will be indicated by the following symptoms: l MIL light on (NAS and EU-3 only). l Default to open-loop fuelling for the defective cylinder bank. l If sensors are crossed, engine will run normally after initial start and then become progressively unstable with l High CO reading l Strong smell of H 2 S (rotten eggs) l Excessive emissions Fuel metering Under normal part-throttle operating conditions the fuel mixture is adjusted to provide minimum fuel emissions and λ = 1). The engine management system monitors the changing engine and environmental conditions and uses the data to determine the exact fuelling requirements necessary to During full-throttle operation the air:fuel mixture needs to be made rich to provide maximum torque. During When the vehicle is braking or travelling downhill the fuel supply can be interrupted to reduce fuel consumption and If the vehicle is being used at altitude, a decrease in the air density will be encountered which needs to be |