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I Guess?? how does the smog pump actually work?
Its purpose is to add fresh air to the exhaust to finish any incomplete combustion. It combines CO ,HC and oxygen (O2) to produce CO2 and H2O. The simpler systems have a smog pump, a bypass valve and a check valve.
The smog pump itself is a simple carbon vane pump. If you really want to piss someone off suggest their smog pump needs oiling. It will destroy the carbon vanes. These can also fail from moisture as in say from the exhaust. This happens when someone removes its belt to save power and leaves the plumbing hooked up. A few months later they'll replace the belt to get a smog check and find the pump has locked up. This is a stupid idea anyway since these pumps typically draw around 1/2 HP.

The bypass valve is used to stop the air injection during deceleration. Ford's name for this is Thermactor Air Bypass (TAB). Since the exhaust is typically filled with unburned gas (HC) during deceleration adding fresh air will cause a backfire. To avoid this the air pump is bypassed by sensing manifold vacuum. Manifold vacuum is at its highest during deceleration.

Downstream of the bypass valve is a check valve. This is simply to stop the exhaust gasses from traveling up the AIR plumbing. If these fail you'll often see the rubber AIR plumbing melt or crack.

On a late models, Ford adds a third valve they call a Thermactor Air Diverter (TAD). During warmup, this valve 'diverts' the air to the ports in the heads. This has two effects. Hopefully, it warms up the exhaust faster. Also, it 'fools' the O2 sensors so the computer will make the engine run rich to allow better cool running.

Hope this helps

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