Air Injection: Description and Operation

This system injects compressed air into the exhaust gasses in the exhaust manifold to extend the combustion process into the exhaust system. The addition of this secondary air helps to further burn the hydrocarbon (HC) and carbon monoxide (CO) content of the exhaust gasses to minimize these pollutants. On vehicles equipped with catalytic converters, this secondary air is also used as the oxygen source for the oxidation process.
Air injection is controlled electronically in response to engine operating conditions in order to maintain oxygen levels in the exhaust stream at the ideal stoichiometric level for catalytic converter operation. Air pump output is controlled by an Electric Air Control Valve (EACV) which is operated by signals from a micro-processor (computer). The computer monitors inputs from two coolant temperature switches, a vacuum switch, catalyst temperature sensor and an oxygen sensor in order to control EACV operation.
Signals from the oxygen sensor are used to control EACV operation when coolant temperature is 109---208°F and catalytic converter temperature is less than 1110°F. Under these conditions, all of the remaining sensor circuits are open and the computer turns the EACV ``on and off'' in response to oxygen sensor signals. When the sensor indicates low oxygen concentrations in the exhaust, the computer energizes the EACV and air pump output is delivered to the injection manifold. When the sensor indicates high oxygen concentration in the exhaust, the EACV is de-energized and air pump output is diverted to the air cleaner.
When coolant temperature is 64---109°F, coolant switch 1 is closed completing its circuit to ground, the EACV is energized, and air is injected continuously. When coolant temperature is below 64°F or above 208°F, coolant switch 2 is closed, or if catalyst temperature exceeds 1445°F the thermo sensor circuit is completed to ground, and the computer will de-energize the EACV. If there is a sudden increase in manifold vacuum, such as during deceleration, the vacuum switch circuit is momentarily completed to ground and air pump output is diverted to the air cleaner.