THERMACTOR System: Operation: Notes

Inlet air, flowing to the air pump, is drawn through a centrifugal air filter fan. The air pump then supplies air under pressure to the exhaust port near the exhaust valve, by either an external air manifold, or through an internal drilled passage in the cylinder head, or in the exhaust manifold. The pressurized air, combined with the hot exhaust gases, create a secondary combustion stage that produces carbon monoxide and water.

In the MTA system, air can be by-passed to the atmosphere by a Thermactor Air By-Pass Valve, and/or directed near the exhaust manifold, or to the underbody catalytic converter. Some models may use a Combined Air By-Pass/Air Control Valve.

In the Thermactor II system, natural pulses present in the exhaust system are used to pull air into the exhaust manifold through a PAV. The pulse air valve is connected to the exhaust manifold with a tube, and to the air cleaner with a hose.

In the Extended Idle Air By-Pass System, a normally closed Idle Tracking Switch (ITS) opens when the throttle returns to idle. This signals the EEC module to de-activate the normally closed solenoid valve. Vacuum is removed from the normally closed by-pass valve, causing thermactor secondary air to be released into the atmosphere.