EGO clogging.

[Craig Pugsley]

> 
> > 
> > i/  We all know the 'characteristic curve' of an O2 sensor, but how much
> >     effect does the actual exhaust temperature have on it's accuracy,
> >     and also does a HEGO have some way of regulating it's temperature?
> 
> Most HEGO's I've seen hook up to +12v, and they use the positive temperature
> coefficient of the heating element to regulate the temperature.

Aaahh!! Neat!

> EGO sensors aren't affected by temperature much for its real 'trip point',
> but temperature is the largest contributor to voltage variations in the
> sensor. GM tends to use the voltage level out of the sensor for more
> than just 'RICH/LEAN', so they use various compensations to predict
> the O2 sensor temperature.

So the 'trip point' is much the same but the overall voltage is lower at
lower temperatures.. The curve is 'squashed down' if you will.
So, with a thermocouple and an EGO you could (with some processing) find
out the A/F ratio.

How does a UEGO work?

> > ii/ What about electrical effects changing the sensor's voltage? eg
> >     thermocouple effects between the exhaust and the engine. Should
> >     the sensor be used in a 'balanced' set-up.
> 
> Normally, between the block and manifold there's little difference. GM
> attaches one end of the diff amp (- end) to the engine ground. The
> other end goes to the O2 sensor. The - end should go to a good engine
> block ground.
> The LM1964 is an amplifier designed especially for amplifying O2 sensor
> signals. It's in National's special purpose devices book (Linear 3).

That's what I thought might happen - obviously any thermocouple effects
would be minimal, but it doesn't hurt to ask.

Craig.

pugsley at trl.oz.au