WPSLPGExhaust Gas Oxygen (EGO) sensor Information

[ext-peter.betts at nokia.com]

LONG QUESTION, but please help :-)

>From reading the information sent by Darren (not included here) I am rather
dissapointed regarding the AFR meters.

The opinion seems to be that the AFR meters with a 10 LED bar graph
representing a voltage range between 0 -> 1 V are a waste of time. One only
needs a 3LED system showing RICH, STOCH and LEAN.

Also If I have understood correctly the O2 sensor is only used in Closed
loop operation (i.e. Cruise) so is it any use in open loop, WOT? Surely we
are more interested in the O2 content under WOT to prevent detonation so how
does the O2 sensor help us here if you are saying it's not used open loop?

I had previously thought the following but I guess that's complete rubbish?
I'm confused! HELP. I've read the archive but I need a definitive answer and
concise.


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Common aftermarket A/F meters only indicate how the mixture is on a relative
basis, and that's all these cheap devices are good for. If you want accuracy
you are talking £3K plus. However they are still useful. They really only
indicate the O2 sensor reading and map this to an Air/Fuel ratio.

Set your boost controller to a stock level. Say 13psi and go for a run.
Under normal driving/blipping of the throttle you'll see it flicker up and
down. This is due to the ECU being in closed loop mode and it trying to vary
the AFR all the time to keep economy good.

But under a steady load (i.e. put your foot down on the accelerator and
build up some +ve boost) it switches to open-loop mode and you should see a
pretty steady reading. It should not dart around or more importantly drift
up or down. Make a mental note of which LED was lit. The car should always
try to maintain this level if fueling and the fuel maps are correct. Ideally
this should be 14.7, i.e. say the 5th LED of a row of 10 but due to slight
inaccuracies it might be a bit higher or lower. Again it's the relative
changes you're looking for.

In other words, if you are seeing, say, 7 out of the 10 leds lit up under
moderate acceleration, and the lights fade away, one by one, as the revs
climb, you know instantly that you have a problem, the car is unable to
sustain enough fuel and over time it begins leaning out. Not good.

In another situation, if you now raise boost levels, and your mixture shows
(again relatively) leaner, you know that you need to provide more fuel. It
would be nice to know absolute values but that is an expensive proposition.

Remember the oxygen sensor needs to be hot so allow a good 5->10mins of
driving before making sense of any readings. 

QUESTION: Is the above reasonable? Do O2 sensors vary between cars (the
voltage output levels)? If so how do these aftermarket bits of kits work and
they don't have any kind of fine tuning built in? 
************************************************************************

I have a 1995 Toyota Supra Twin Turbo which I believe has a heated oxygen
sensor (HEGO). Anyone with the same car know detailed information about the
sensor?
How do I relate the sensor output to rich, ideal or lean. I had thought it
was a 0->1V
output signal and it normally sat at around 0.5V for Stochiometric and about
0.8V under WOT on a stock car.

This doesn't seem to be true as the AFR meter that I built assuming the
above seems to indicate >1V RICH! 
BUT I would just like to check with the rest of you if you have more info
for me.

I am talking about WOT (Open Loop) and not closed loop as I realise the
signal oscillates under closed loop cruise conditions to *average* out to
stochiometric (Don't flame me here it is a very simple generalisation). It
should be steady at open loop. (Shouldn't it?)


Anyway I'm trying to make an AFR meter/monitor using a PIC chip to make a
more intellegent sense of the data from the sensor but it seems I may be
wasting my time as the sensor is not good enough.

Pete
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