what does teh air pump do?

 

On an S4 and S5 RX-7 it injects air into the main catalytic convertor to help with the emissions. It speeds along the catalyst reaction. Usually your main catalytic convertor will not last too long with the air pump disconnected. On an S5 RX-7, it is also involved with the actuation of the 5th and 6th ports on a N/A engine. You probably should use the search function as this has all been covered many times.