O2 sims

[Len Sabatine]

     GM Post HO2S Do Switch. The PCM is looking for at least a 60% 
Calculated Oxygen Content Ratio,
     as compared to Pre H02S. If the Post O2s have a fixed reference the 
PCM will start Subtracting
     fuel then set a Code with "Freeze Frame" data as well. I just fixed 
the same problem on a 97
     Z28. Bank 2 #2 Ho2s was reading a Fixed 447 MV . No Good.
     An O2 Sim needs to vary the V Signal within the Expected range that 
the PCM wants to see in CL.
     If the PCM doesn't get what It wants , It will just Subtract fuel and 
react accordingly.
     Len

>The info I've heard from a *Ford* tech friend is that the rear, post-cat 
>sensors do not switch,
>but so fluctuate a bit.  Supposedly the training he had from *Ford* told 
>him that the ECM would
>only look to see that it didn't switch...
>
>I have no clue, just spreading rumors.
>
>Squash
>
>--- Brian L Massey <blocklm at juno.com> wrote:
> >
> > On Fri, 14 Sep 2001 10:16:00 -0500 Gary Heuston
> > <gary.heuston at afwa.af.mil> writes:
> > > you
> > > need to
> > > attach O2 simulators to the wiring to fool the computer into
> > > thinking
> > > the second
> > > set of O2's is working properly...I was just wondering if there was
> > > a
> > > way to
> > > build these on your own instead of paying $90 for a pair...
> >
> > I sure would try some 0.5 V fixed voltages for these posterior sensors
> > before spending any money. I was under the impression that a code would
> > be thrown if the *post*-cat sensors *weren't* at a stable value somewhere
> > near stoich. I suppose if the ECM designer was trying to be clever, he
> > would watch to see if the sensor appeared to be warming up, but I doubt
> > if even this is workable; in control system restarts, you can never
> > assume a cool-down before restart (as much as we might like to for
> > convenience). So I think it would be problematic to look for anything
> > *but* a stable near-stoich reading from the post-cat sensors. Well, check
> > that; they could look for an open sensor connection, but that would be
> > taken care of with the 0.5 V source having a somewhat low impedance.
> >
> > That's why I've been puzzled each time someone mentions these
> > "simulators". Has *anyone*  tried just a simple static voltage of around
> > 0.5 V, preferably buffered?
> >
> > Brian
> > ________________________________________________________________
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>
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