O2 Sensor Open/Close Loop

[Mazda Ebrahimi]

Scot A. Sealander wrote:
> 
> kleenair at ix.netcom.com wrote:
> 
>  [Big snip]
> 
> > Regarding what OEMs
> > do on late model vehicles, I had a 1996 3.8L Buick on the dyno, which
> > maintained its closed loop operation at WOT.
> 
>  How do you know that it maintained closed loop?  Scan tool? Don't believe
>  it!  In the GM code I have seen, they leave the closed loop flag on, even
>  when it is in PE.... and that is most definitely not closed loop.
> 
> > However, their motive may
> > have nothing to do with peak power.  That may just be a way of protecting
> > the catalyst by reducing excess fuel in the exhaust during extended high
> > engine load periods.
>   Maybe, but I personally doubt it.
> 
> > Also, just because the system stays in closed loop does not necessarily
> > mean actual A/F is 14.7:1.
> 
>   Well, in the normal GM scheme of things, that is untrue.  I have the
>   feeling that open/closed loop operation is not well understood....
>   though I have not looked at any newer code.  My experience stops at about
>   the 1993 model year or so.....
> 
> > If the system is flexible enough, you can
> > make the Rich to Lean transient slower than Lean to Rich transient, in
> > effect raising the average O2 sensor voltage.
> 
>   Is this in reference to the normal dithering of the O2 volts in closed
>   loop?  Making the controller asymetrical?  Some GM systems are that
>   flexible.  The Buicks I have seen are not so flexible.
> 
> > Most systems can also use
> > a different target O2 voltage based on MAP and RPM.
> 
>   Now I was under the impression this was because of the O2 sensor
>   temperature (and the temp effect on O2 sensor volts), not because of a
>   different desired AFR.... The sensor is not very useful very far from
>   stoich, so I don't think trying to stay in closed loop would buy you
>   anything.
> 
> 
>   I have been meaning to make a decent scan tool to watch the O2 controller
>   at work in the ECM under actual driving conditions.  I have completely
>   worked out GM ALDL protocol, but am not really a programmer. :-(  This
>   makes it hard to build a scan tool.
> 
>   Scot Sealander    Sealand at clarityconnect.com

The reference to varrying the target O2 sensor voltage and biasing its 
rich / lean swings was not on any particular system.  I have used two 
different aftermarket systems, one designed for gasoline, the other for 
an alternative fuel.  Both the target voltage and the biased swings have 
a significant impact on A/F ratio, especially with regard to emissions.

Regarding the Open / Closed loop on the 3.8 L Buick, I was using Tech-II 
to monitor the mode of operation AND O2 volts.