wesilva

iTrader: (35)

I have a friend with a 1990 IROC with a Tuned Port Speed Density 350. What has always confused me about his car is that it has an air pump dumping oxygen into the header tubes. My confusion is that if an oxygen sensor makes adjustments to the air/fuel ratio, how can this be done accurately if you are artifically dumping oxygen into the exhaust, not really giving the oxy sensor a true sample of what's happening in the motor. Can someone explain? Thanks!!

88305tpiT/A

iTrader: (2)

there is an offset that gets subtracted from the target O2 sensor reading when the air pump dumps air into the exhaust upstream of the sensor.

wesilva

iTrader: (35)

Thanks 88305. So rumours of gaining a little horspower by gutting the air pump would actually screw things up unless you recalibrated the ECM...correct?

Mkos1980

iTrader: (8)

Once closed loop hits all the air is diverted to the cat anyways

wesilva

iTrader: (35)

At what point does the system go into "closed loop"?

AlexJH

It depends... but when I'm datalogging it usually takes about a minute if I'm driving, 2 mins at idle.

92blue

iTrader: (1)

While the air is being diverted to the headers, the engine is ignoring the O2 reading, as it is in open loop.

While the ecm is listening to the input from the oxygen sensor, air is being diverted to the cat.

TexasSilhouette

iTrader: (4)

The upstream air stokes the fire above the O2 sensor to heat it up to force closed loop sooner, that is the ONLY reason for the upstream A.I.R. (Air Injection Reaction in case you ever wondered why it's an A.I.R. pump and not an air pump). With the advent of heated O2 sensors, the upstream air was no longer required.
Once switched to downstream, the free oxygen in the air is used in the back half of the converter to combine unconsumed fuel (HC) with Oxygen (O2) to form H2O (water) and CO2. That is why we see steam and water dripping from the tailpipe of late model engines.

Sad thing is, because of stupid EPA regulations; even if you install a heated O2 sensor which is quicker and cleaner, you still can't remove the upstream A.I.R. because it came that way. So even though technology has improved, the stupid EPA won't let you update.

wesilva

iTrader: (35)

Thanks for the help, fellas. You set a fuel injection newbie straight.