Elle wrote:
> I don't torque my sensor to spec but go by feel (based in
> experience at this point) instead.

Same here as far as torqueing by feel, though being new to an aluminum
block I did pick up an I-beam type torque wrench when I bought the car.
Will probably use it here.

> Beg pardon.

Hey, no problem!~

> The sensor just juts right into the path of the exhaust
> gases. Where it juts etc. should not look different from
> the inside of the car's tailpipe, AFAIC.

Inside of my tailpipe is pretty black with carbon deposits. I am burning
some oil, though I've never really pinned down how much. Not excessive
for a car of this vintage/mileage. I tend to drive pretty fast, but
generally don't abuse my engine with hard acceleration.

> My 91 Civic's O2 sensor never actually failed. I just chose
> to replace it pre-emptively based on something I think
> Tegger wrote; the great prices at automedicsupply; the drama
> of being stuck in the middle of nowhere (at the mercy of
> god-knows-what charlatans) with a failed O2 sensor;

Not to worry. From the Helm manual for my 1994 Civic, p11-39:

>>>>
ECM Fail-safe/Backup Functions:
1) Fail-safe function
When an abnormality occurs in a signal from a sensor, the ECM ignores
that signal and assumes a pre-programmed value for that sensor that
allows the engine to continue to run.

2) Back-up Function
When an abnormality occurs in the ECM itself, the fuel injectors are
controlled by a back-up circuit independent of the system in order to
permit minimal driving.
<<<<

(I'd expect similar back-up function in any such system designed by
reliable engineers.)

I gotta say, the wealth of information, including troubleshooting
flowcharts, in my Helm manual makes it worth many times the $70 or so
that it cost me.