Michael Benno

I came across this while studying PET (87 - 91) and was curious on how this system works. Rather than feeding supplemental air to the cats, in this case it looks like the air pump is feeding supplemental air to the exhaust ports? I presume this is to help lean out the readings at the O2 sensor but not sure why. Would anyone be willing to give me a little education on how this particular system works and any benefits of having this if I am not using cats (or old cats that need supplemental air). And, was there a coding change in the ECU to with with this system?


In my 88, I have removed the air pump system all together, but curious nonetheless

FredR

Michael,

My 90 S4 [non cat] was originally configured this way. There is no O2 sensor and exactly what this system was intended to achieve remains a mystery to me given cats were compulsory in the States by then [I think]. The plumbing does indeed take air into the exhaust ports and I could only assume that it was intended to fudge some legislation somewhere. for better or worse I removed the superfluous crap but left the air piping attached to the motor albeit blocked the inlet from the air pump.

To be fair, my exhaust at idle is a bit heavy especially when the car is in the garage- whether or not this kit would have made it more palatable remains to be seen.

gazfish

I believe it's to help continue the combustion of the hot gasses in the exhaust to reduce emissions.

V2Rocket

https://en.wikipedia.org/wiki/Secondary_air_injection

Dave928S

The early CIS also have it, with the air fed to a drilling from front to back of each head which skims past the exhaust ports, and a small bleed hole through the port wall from that drilling.



^^ Drilling from front to back ... light is from an exhaust port drilling.



^^ Exhaust port bleed hole.