[Diy_efi] Dead O2 sensor values

[Bernd Felsche]

Kris Sundell tapped away at the keyboard with:

> What kind of values will you get when an O2 sensor goes bad?  Does

All sorts. It depends.

> the voltage go up, down, or does it depend.  We're trying to hook
> this into an EFI setup and want to have some safeguards so that we
> don't lean out the engine if a sensor fails.

The preferred traditional method of detecting a faulty sensor is to
count the rate of lean-rich voltage transitions. If none of these
happen when they notionally should, then the sensor is faulty.

Assuming that the sensor is producing a sensible output after
warm-up is one of the failings of Digifant II in VW's. Fortunately,
the ECU detects disconnection and apparently falls back to a
slightly-rich fuel mixture. The car is basically undriveable until
you unplug the sensor; after which it runs somewhat better than
"normal".

-- 
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