Originally Posted by
zip439
I get the secondary pump coming on briefly after driving the car and then coming to a stop at idle as a short shot of fresh cool (relative) air into the exhaust could help cool the manifold. But, wouldn't injecting air into the exhaust any longer than that cause the O2 sensor to signal a lean condition and increase fuel when it is not necessary? Padgett was idling for fifteen minutes. Could the secondary pump find the increase in exhaust temperature over that 15 minute time frame and think it is time to turn on for a couple seconds? or longer?
what it does (if i recall correctly) is start to richen the a/f ratio then turns on the air injection pump and watches for that a/f ratio to drop. if it does drop then it allows the ecu to verify the secondary injection system is working properly. as far as i can tell it only runs this system for testing purposes after the engine is warm. I'll have to go back and read through all my service studies from years ago if i can find them.things like this that are so specific i try not to remember cause if i don't remember even one thing exactly the way it is the whole testing procedure is not longer any good so i prefer to just go back and read data and perform tests word for word.