O2 sensor display.

[Steve Gorkowski]

Very good statements and keep them coming we need people to rock the boat to
come up with new ways of looking at things so new designs can be built.

Steve

G. Scott Ponton wrote:

>     Ok. Mostly I am just a lurker. I am sure some of you have read a few of
> my posts. Up til now some have been received with very little "respect".
> This seems to be quite common with anyone who wants to add something to the
> discussion which doesn't fit the small area of expertise some on this list
> have. Realizing this must sound a little harsh let me try to reduce the
> impact to a few egos by saying I am quite impressed by the wealth of info,
> time and effort spent on several of the projects which are ongoing topics of
> this list.
>     There seem to be a lot of misconceptions about how an EGO sensor
> actually works. Maybe I am wrong and everyone really does understand but
> some of the posts I have read lead me to wonder.  EGO sensors (Palladium
> type, which includes wide band) don't actually measure the amount of oxygen
> in the exhaust. They compare the oxygen content of the exhaust to the oxygen
> content of the air around the sensor. This pretty well negates variences in
> oxygen content from one moment to the next.
>     The combustion of gasoline (ideally, lets not get all tied up in minor
> details here.  The correction factors needed for perfection are not within
> the scope of the technology we are currently working with.) does NOT require
> a perfect A/F ratio to occur. Carburation has proven that for the past 90 or
> so years. Provided the A/F ratio remains between 15.5:1 and 11.5:1 most
> engines will run well enough for the average person to never know they have
> a problem. Also the EGT, for a particular engine, varies by less than 5%
> within these ranges. (different engines may have different EGTs for the same
> A/F ratio.)
>     A "wide band" EGO "switches" ( using the term "switches" to attemp to
> simplify the discussion. Center of range = 14.7:1 approx. Where 14.7:1 is
> the agreed upon IDEAL A/F ratio for complete combustion of gasoline as a
> fuel.) from rich to lean at approximately the same point its standard
> counterpart does. Roughly 1/2 of its operational scale. So what is the real
> advantage? It gives you more room to see A/F variances? Consider this if you
> will. In an IDEAL situation, from the point where gasoline is too lean for
> combustion to the point where it is too rich, the center point is not 14.7:1
> !!!!!!!!!!!
>     At A/F ratios of 16:1 the misfire rate is nearly 70% at 10:1 it is just
> reaching the same 70%. At both ends of the scale an EGO measures the same
> oxygen content in the exhaust right? Wrong ............... the oxygen
> content in the exhaust of an engine which is too rich is less than one which
> is too lean at the same rate of misfire. An engine which misfires by being
> too lean dumps an entire load of unburned oxygen into the exhaust. Where as
> a engine which is too rich burns some part of the fuel leaving less oxygen
> in the exhaust. (Naturely if it is so extreme in either direction as to not
> burn at all this changes as the engine becomes an air pump.) So what good it
> an EGO sensor when it comes to tuning an engine?  None! It is a tuning aid
> intended to reduce emissions. Because the "air" we breath isn't all oxygen
> we have to make some allowances for other emissions created by its
> combustion.
>     With respect to an EGO sensor I have spent many hours testing and
> playing with this particular sensor. I have run temp correction and
> correlated the voltage to a A/F ratio. This was done by first calibrating a
> MAF and an injector set. By using a flow bench then calculating the air
> density, the frequency of the MAF was charted. Using an injector flow test
> rig allowed the amount of fuel to be accurately calculated. By knowing the
> injector pulse width, fuel pressure, specific gravity of the fuel, and the
> air density entering the engine it is fairly easy to calculate the A/F
> ratio. Now some interesting things were learned with this setup.
>
> 1. EGT has a minor effect on the output of the EGO sensor (this next part is
> VERY important) within the NORMAL range. This doesn't include extremely lean
> and/or rich A/F mixtures. Both of which affect more than just the EGT.
> 2. A "wide band EGO is easier to read simply because its operating
> parameters are spread across a wider range. It still functions on the same
> principle as a "normal" sensor (Read palladium here).
> 3. The sensor does NOT (once again read palladium) switch back and forth
> between rich and lean. This is a function of the ECM/PCM.
> 4. although .5 volts is pretty close to stoich the voltage values are NOT
> linear. .01 volt is not the same amount lean as .99 is rich.
>
>     There are sensors which "switch" back and forth. These are a different
> composition and are mostly used by the Japanese at the moment. Their
> measurement range is very narrow. Less than 1 point change in A/F ratio.
>
>     I hope this will help some on the list. I also expect there will be a
> few souls who will take exception to what is written here. So be it. I will
> be more than willing to elaborate in much greater detail on the subject of
> gasoline combustion in an internal combustion engine, but the post is liable
> to be the size of a book in order to "qualify" all the variables which
> effect real world combustion. Also many of the variables have a negotiable
> effect on this discussion.
>
> Scott