It pumps smog from inside your engine and pumps it outside into the air. If Cali would get red of smog pumps on all their cars, the smog would be eliminated!
OK enough humour, the way I understand it is it pumps air (oxygen) into your exhaust to try to completely burn the unburned hydrocarbons in your exhaust, hence to lower the smog by having a more complete burn. I dont think it adds any power to your engine. Maybe some of our more knowledgible friends can add to this, or, set me straight.
I think they raise catalytic converter temps the first few minutes the car is running, then do nothing once the cat can keep warm on its own.
The old belt driven ones divert the air back into the air cleaner once warm. The newfangled electric ones just shut off.
I would imagine if you get your tailpipe sniffed when the car is fully warm, you don't need it there to pass a smog test-- except, of course, that you aren't allowed to take it off.
It supplies fresh air, which contains oxygen, to the catalyst. This oxygen helps the chemical reaction that takes place in the catalyst to operate more efficiently.
In my 1988 Mustang, the smog pump system, called Thermactor Air by Ford, can operate in 3 modes:
In the upstream mode, used at cold startup, EDIT: after the engine has been idling for 30-45 seconds also, the air is injected at the cylinder heads. This apparently causes the exhaust gasses to continue burning in the exhaust manifolds, since they didn't burn completely in the cylinders due to the cold startup and rich mixture.
In the downstream mode, used after the engine has warmed up, the air is injected at the cats. This air causes the cats to work more efficiently, as I mentioned above.
In the bypassed mode, used EDIT: during deceleration, to prevent a backfire, the air is just dumped out of a hole in the valve just after the air pump.
[ April 07, 2005, 04:14 PM: Message edited by: brianl703 ]