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[gsizoli]

Hi!

This quetion is addressed for mechanics.
Does anybody know what is the real function of the secondary air injection system?
As I know it's heating the cats till the operating tempearture is reached, (By feeding air into the exhaust manifold (secondary air), CO and HC are oxidized through afterburning at temperatures over 600°C to form water and carbon dioxide. The exothermal reaction also increases the exhaust gas temperature, which warms the catalyist more quickly.
) but a guy says it'"s not heating (it's heated by the exhaust gas) just blows air which mixes with the exhaust gas to protect cats from damage.

[oceansoul]

i dunno what they do, but many people take them out and notice no difference

[markey mark]

its to fast warm your cats to keep emmisions down ! was only for banding at the time  

[RobG]

  The secondary air injection is a system where by air is blown into the exhaust manifolds for the first few minutes of startup, any unburnt fuel then ignites in the front pieps and the cats heat up a bit quicker.

This is done by a large blower which is mounted in the passenger side front wing, the air blows through a tube into the vac operated shut off valve mounted on the radiator (vac operated so when at Wide Open Throttle there is no air injection plus there is ECU control to via a vac valve).

Courtesy of Marks DTM Oct, 2006

[feeutfo]

its only purpose is to make people post questions on here about "whats that horrible noise, whats it for, how do i get rid?" so all can give a unanimous reply.... Unplug it! Thats all it does. :-)

[Martin_1962]

Usual use more energy to create less emmisions 'dangle berries'

[magnul]

And what's wrong about reducing the CO and HC emissions?

[TheBoy]

And what's wrong about reducing the CO and HC emissions?

It doesn't reduce CO(x) or HC though.  It reduces NO(x)

[magnul]

And what's wrong about reducing the CO and HC emissions?

It doesn't reduce CO(x) or HC though.  It reduces NO(x)

Reducing CO and HC requires oxidizing conditions (as made by the secondary air). Reducing NOx requires reducing conditions (as made during the rich cycles at closed loop).

[TheBoy]

And what's wrong about reducing the CO and HC emissions?

It doesn't reduce CO(x) or HC though.  It reduces NO(x)

Reducing CO and HC requires oxidizing conditions (as made by the secondary air). Reducing NOx requires reducing conditions (as made during the rich cycles at closed loop).

Actually, you're right - my mistake for not reading the question fully before reading...

[TheBoy]

But to answer your Q, it doesn't really help enough with emissions to make it worthwhile.  Its removed from later UK spec cars.

[magnul]

AFAIK, at least the 2.2 hasn't got it. I'm a bit curious what replaced it though. Better engine management, or some pre-cat on the down tube or something?

[TheBoy]

AFAIK, at least the 2.2 hasn't got it. I'm a bit curious what replaced it though. Better engine management, or some pre-cat on the down tube or something?

nothing replaced it.

[magnul]

Well, it was required to pass Euro2 emissions, so I guess something was done to still pass the later Euro emission codes.

[markey mark]

Well, it was required to pass Euro2 emissions, so I guess something was done to still pass the later Euro emission codes.

yep went twin cats and dbw throttle and cpp