Closed loop/open loop @ WOT

[Master of Disaster]

I think you should sell your Supra and buy something American, with 
an LT1 or LS1 engine. :^)
They stay closed loop at WOT, or thus I have been led to understand.
I am not bad-mouthing the Supra-- it's a beast, but if it goes open 
loop at WOT, I don't want one.




>Date: Wed, 2 Aug 2000 10:58:34 +0300
>From: ext-peter.betts at nokia.com
>Subject: RE: WPSLPGExhaust Gas Oxygen (EGO) sensor Information
>
>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.
>
>
>************************************************************************
>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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