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

[Eric Renneisen]

LaR wrote:
> 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 and
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.

Eric Renneisen
'93 S4
'86 urq
Chattanooga, TN