O2 sims

[Jay Vessels]

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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>>=====
>>Trains, Trucks, and EFI at http://www.trailrunners4x4.org/users/realsquash
>>
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