EGO and the Smog Pump

[Christopher G. Moog]

Steve Meade wrote:
> 
> >
> > Robert Harris wrote:
> > >
> > > Dah, correct me if I am wrong ( aw go ahead and do it anyway)
> > > but doesn't the EGO sense total oxygen in the exhaust stream
> > > and get "happy" around stoic?   If true, then when we shove
> > > extra oxygen via the smog pump into the exhaust, do we not have
> > > to shove unburned fuel from a too too rich mixture into the exhaust
> > > to make shore that the result is stoic at the sensor?  Am I missing
> > > something here or is the total extra oxygen so low that it doesn't
> > > make much difference in the fuel consumed??
> >

Many cars route the air pump outlet as follows:

1. To the exhaust port when first started.  This allows unburnt HC to
burn lowering emissions and heating the cat(s) and EGO sensor.  The
engine is operating in open loop and the EGO is not functioning.

2.  To the cat once warmed up.  The engine controls will keep the engine
slightly rich producing CO.  The CO scavenges the oxygen released when
the three way cat reduces NOx to nitrogen and oxygen.  This helps
prevent the reverse reaction (oxygen and nitrogen recombining to form
NOx compounds).  The air pump outlet is sent to the cat (at the midpoint
of the cat, where oxidation is occuring) this helps to burn any HCs and
to oxidize any remaining CO to CO2 (and yes some of the nitrogen and
oxygen are recombined to form NOx but the metals used don't encourage
this reaction).  Since the cat is down stream of the EGO the sensor is
reading oxygen out of the engine.