Whats the "air pump" for?

[Nippon]

I've had several Honda's in the past. Namely a few Preludes and one Accord. (only car make I've ever owned). They were all older models of course. I see you guys talking about air pumps from time to time and I've seen it in the Majestic Honda parts list.

Whats the air-pump in an S2000 for? What does it do? How does it work?

Thanks

[gomarlins3]

This may help:
http://www.s2ki.com/forums/index.php?showtopic=87084&st=0&#entry1083027

[repiv]

That thread was pretty early on in the S2000s life and several things said there are inaccurate. For one thing the air that is pumped by the secondary air pump actually goes into the EXHAUST manifold to help complete the combustion of unburned gases during the warm up phase. This improves catalytic converter efficiency at a time when exhaust gases are quite rich. It was Peter who corrected me on that. I guess we were all novices at time or another. :o
After the engine has done its initial warm up, the secondary air injection system stops working. It utilizes a system of vacuum tubes and cannisters to initiate the opening of a valve that lets the pumped air into the exhaust. Since it's part of the emissions system of the engine, it is monitored by the ECU. If you remove any part of this system, you have to find ways to fool the ECU so it doesn't throw a CEL.