[urq] O2 sensor output, WAS: I'm SO close to giving up - Part 2?

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Tue Apr 19 20:16:31 EDT 2005

... why is it that it seems folks seem to be dropping the relationship
to the OXS Frequency Valve duty cycle?  I don't know for a fact that it
is the culprit, but it should be at least as valid a theory as the fuel
pump petering out or an engine misfire.  I looked to the Bosch handbook
to see what the OXS signal does in a misfire condition and found nothing
... but it has been my experience that a misfiring cylinder reports a
rich signal via the OXS.  

Funny, I've had grandiose plans to instrument the crap out of my engine
... pressure transducer to monitor fuel pressure (and/or control
pressure), duty cycle on the OXS Freq Valve, Wideband OXS and EGT on
each cylinder ... all that to monitor the stock CIS!  If I decided to go
Megasquirt or EFI332 I was thinking it would be great to have "ION"
feedback for knock sensing and mixture evaluation ... 

Steve B
San Jose, CA (USA)
> > If it were spark, you'd see rich condition. So
> > must be fuel.
> Would it?  I've always wondered about this.  The O2 sensor simply
> reports the difference between oxygen content of the exhaust stream
> oxygen in the ambient air, right?  Assuming this is the case, and you
> have a spark problem, you would have unburned fuel but also *unburned
> oxygen* in the exhaust.  Wouldn't the sensor report this as an
> excessively lean condition, provided that the unburned mixture isn't
> ignited in the manifold or turbo?
> I've got a little A/F meter that reads the O2 signal, and I've often
> wondered about how to interpret it when troubleshooting a problem.

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