O2 sims

[Len Sabatine]

     As indicated , the C1 Value tweek will alter the freq - switching time.
     A bit of getting creative with C1 area should allow additional varying
     of the signal response. Some logging of the secondary O2 signals
     prior to any mods will be a good basis for comparison to get the
     ramp- slope shape the PCM wants to see over time. This is more
     critical in OBD2 because of more intensive built in O2 Diagnostics.
     There's lots of examples and a 555 calc SW floating around
     on the web. Many times , simple is much better.
     Len

>Hi there!
>
>I thought about a simple oscillator to simulate a wondering O2 signal, but
>someone beat me to it:
>
>http://www.bobblick.com/bob/auto/o2sim.html
>
>This guy basically built a 555 circuit and trimmed the output accordingly.
>Not necessarily the most graceful design, but workable.  I'd say any 555
>timer circuit set to oscillate at 10Hz or so (20 crossings / second @ 10Hz)
>with some output shaping would do the trick.
>
>Jay Vessels
>1982 Chevrolet S-10 Sport, 2.8V6 TBI
>1994 Chevrolet Cavalier Z24 Conv., 3.1V6 MPI
>
>
>At 06:02 PM 9/14/01 -0400, you wrote:
> >     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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