Zirconia O2 sensor alternate modes of operation

TBK terryk at foothill.net
Sun Feb 22 18:39:12 GMT 1998


I am starting to get outside my level on knowledge on the operation of the
ECM, but I don't think it is current.

I have seen several comments about not reading the O2 sensor voltage, due to
potential damage. But I think this is related to low impedance ohmmeters. A
high imp meters (above 1Mohm/volt) would be ok and I do it all of the time.

As far as reliable measurements, the system is a bang-bang system. It knows
.45V is about 14.7 but it is not linear on each side. So GM slams the
mixture rich and lean to swing back and forth across that point.

It kinda' like the Braille method of walking down a hall. Swing the cane
left and right. When the swing is equal on both sides, you are in the center
of the hall. This is called bang-bang in electronics. Do it fast enough and
the average is pretty damn close to the goal. If below .45V, add fuel until
above, and then remove fuel until below .45V and then on and on.

That's about the best I can do on this.

I do know that an O2 sensor can be calibrated and a correction factor
generated. But that would take some expensive equipment and each sensor
would need it's own correction. So bang-bang is a better solution for mass
production. But to assume it is linear is incorrect.They do have good
repeatability. So once you know some value of Voltage vs AFR, they will give
the same readings over and over.

Anybody?

TK
-----Original Message-----
From: Zack <zubenubi at inetport.com>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Sunday, February 22, 1998 10:23 AM
Subject: Re: Zirconia O2 sensor alternate modes of operation


>TK,
>
>Ahh, so the GM ECU >doesn't< read the current.  That's what I thought.
> So anyway, back to my original question, if I bias the sensor with a low
>voltage and read the current flowing through it, do I have the potential to
>damage it in any way?  And if not... over what range of A/F ratios can I
>get a reliable measurement?
>
>Zack
>
>----------
>> From: TBK <terryk at foothill.net>
>> To: diy_efi at efi332.eng.ohio-state.edu
>> Subject: Re: Zirconia O2 sensor alternate modes of operation
>> Date: Sunday, February 22, 1998 1:13 AM
>>
>> I think it is .456V supplied through 1Mohm. When the sensor heats, it's
>> resistance drops and can now overcome the bias voltage. The .456V is just
>> there to fool the ECM until the sensor is warm.
>>
>> Right or wrong Peter?
>>
>> TK
>> -----Original Message-----
>> From: Zack <zubenubi at inetport.com>
>> To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
>> Cc: nacelp at bright.net <nacelp at bright.net>
>> Date: Saturday, February 21, 1998 10:57 PM
>> Subject: Re: Zirconia O2 sensor alternate modes of operation
>>
>>
>> >Bruce,
>> >
>> >So you're saying the GM units bias the sensor and read the resulting
>> >current?
>> >Interesting, I didn't know there were any production cars that used that
>> >method.
>> >
>> >Zack
>> >
>> >----------
>> >> From: bruce plecan <nacelp at bright.net>
>> >> To: diy_efi at efi332.eng.ohio-state.edu
>> >> Subject: Re: Zirconia O2 sensor alternate modes of operation
>> >> Date: Sunday, February 22, 1998 1:11 AM
>> >>
>> >> In the GM applications I've worked on, all had a .44v applied to
>> >> the O2 sensor, didn't matter if they were heated or not.
>> >> Bruce
>> >
>>
>




More information about the Diy_efi mailing list