Closed-Loop Fuel Metering System
TWC systems require the
air-to-fuel mixture charged
to the engine to be controlled
precisely if they are to
This is accomplished by
positioning an oxygen sensor
in the exhaust manifold to record
the discharge O2 content. Air flow to the engine is monitored as it responds to variations in throttle position and load.
Computer control regulates the fuel metered to the engine to control the reaction stoichiometry.
Nevertheless, a TWC catalyst “sees” an exhaust composition that fluctuates between rich and lean.