O2 Swing Points

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01-15-2013
EagleMark

O2 Swing Points

I found some conflicting info on O2 swing points in searches. Starts with this:

Quote:

Table {B4105} “O2 Switch Point”:
Set all values to 450mv. This value (450mv) equates to 14.7 AFR and has
been found to enhance the smoothness and the accuracy of the LTFT
values.

Thought the .450 was Stoich and not 14.7 to 1 AFR? Although Stoich of E00 gasoline is 14.7 AFR.

If changing AFR to fuel of say E10 which is 14.2 then Stoich would be the same .450 mv, that is what we're shooting for correct? Stoich?

There's a very small window of accuracy in narrow band O2 sensors which .450 is right in the middle of. So this was my next point of conflict"

Quote:

The O2 switch points are basically the voltage the computer will switch around while in Closed Loop. So if you want a leaner or richer AFR then adjust your switch points accordingly. I have mine set to switch around ~15.2-15.5 while in a light load, which in my case is ~ 250mV. It is good for a couple more MPG.

Since this is outside of accuracy of NB it could not be accurate, but if set with WB could it work?
01-15-2013
bobdec

As I understand it ".450 V = 14.7 AFR" is gasoline only (E00) stoich, and .450 V = 14.2 AFR would be a E10 stoich. It's the design of automotive O2's that make .450 = stoich. Previous to ethanol fuels I guess all automotive tuning people just picked up on calling 14.7 = stoich and it has stuck. A car running E10 will still manage the rich/lean based on the .450 O2 reading. Now that leads into your second question.. I only have OBD1 but, it's similiar to OBD1 below are pics of stock and performance tune fueling tables "Closed Loop Mode Vs Airflow" and "Fast O2 rich/Lean Vs CL Mode" you can see the stoich switches on the lean side at idle and goes richer at low AFGS flows then goes to 451 after 64 AFGS, My performance tune (with HotCam and 1.6 RR's) is leaned out throughout all the ranges. I have also noticed GM uses different voltage values in the stock tunes for the manual (M6) cars Vs the A4's. I assume lots of trial and error to get the stock settings.

Here is stock..

http://i298.photobucket.com/albums/m...ps1e2c15bf.jpg

And here is a performance tune.

http://i298.photobucket.com/albums/m...ps4d1d109d.jpg
01-15-2013
1project2many

If you think of it, really, the NB is least accurate at stoich. Why? Because any voltage ranging from .25 to about .65 could equal stoich. The reason for switching is to keep ecm "in the region" where O2 voltage equals stoich. Moving your switch point outside that range requires greater accuracy in keeping the fuel delivery and O2 feedback closer to each other. The amount of change in AFR vs the amount of change in voltage is what needs to be dealt with. While the ecm is still adjusting fuel lean -> rich -> lean to make voltage swing below -> above -> below switch point, the amount of change in AFR is greater when voltage switches from one direction to the other. Tighten up the loop and allow less variation to reduce the AFR swing and keep voltage swing closer to switch point.
01-15-2013
EagleMark

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Quote:

Originally Posted by bobdec

As I understand it ".450 V = 14.7 AFR" is gasoline only (E00) stoich, and .450 V = 14.2 AFR would be a E10 stoich. It's the design of automotive O2's that make .450 = stoich. Previous to ethanol fuels I guess all automotive tuning people just picked up on calling 14.7 = stoich and it has stuck. A car running E10 will still manage the rich/lean based on the .450 O2 reading. Now that leads into your second question.. I only have OBD1 but, it's similiar to OBD1 below are pics of stock and performance tune fueling tables "Closed Loop Mode Vs Airflow" and "Fast O2 rich/Lean Vs CL Mode" you can see the stoich switches on the lean side at idle and goes richer at low AFGS flows then goes to 451 after 64 AFGS, My performance tune (with HotCam and 1.6 RR's) is leaned out throughout all the ranges. I have also noticed GM uses different voltage values in the stock tunes for the manual (M6) cars Vs the A4's. I assume lots of trial and error to get the stock settings.

Here is stock..

http://i298.photobucket.com/albums/m...ps1e2c15bf.jpg

And here is a performance tune.

http://i298.photobucket.com/albums/m...ps4d1d109d.jpg

That kinda proves my point that .450 is Stoich and has nothing to do with AFR! Dam internet rumors again...

The CL Vs Airflow (also differant names in differant masks) is becuase Narrowband o2 sensors have different voltages for stoich depending on how much airflow there is, this table compensates for it.

As 1project2many describes tighening up the swing points keeps closer to Stoich. Seems the newer and newer calibrations do not even use differant values there. High and low are the same. When I set mine to .450 on both sides my data is much cleaner.

Here's a graph of why I'm leary of changing higher or in your case lower to acheive a differant AFR. Just so inaccurate outside center of what some charts show as 450 and some 500.
01-15-2013
RobertISaar

Quote:

Originally Posted by EagleMark

That kinda proves my point that .450 is Stoich and has nothing to do with AFR! Dam internet rumors again...

The CL Vs Airflow (also differant names in differant masks) is becuase Narrowband o2 sensors have different voltages for stoich depending on how much airflow there is, this table compensates for it.

As 1project2many describes tighening up the swing points keeps closer to Stoich. Seems the newer and newer calibrations do not even use differant values there. High and low are the same. When I set mine to .450 on both sides my data is much cleaner.

Here's a graph of why I'm leary of changing higher or in your case lower to acheive a differant AFR. Just so inaccurate outside center of what some charts show as 450 and some 500.

that chart is incredibly exagerated... it's got the right idea, but it's too extreme. it's implying any AFR(let's assume E0 gas) outside of 14.3-15.2 would show absolutely no voltage difference when going richer or leaner... it's just not true.

also, i wouldn't say that narrowbands have different responses depending on airflow.... but they do have different responses depending on how hot they are. airflow is a decent indicator of how much heat would be going into it.

http://i.imgur.com/CjbzN.jpg

i've had somebody compare that against a wideband and it came out accurate ~90% of the time...

O2 swing points are actually one of the first things i "fix" in a calibration...
01-15-2013
1project2many

Right on the money. True NB graph is different and for most AFR there is a voltage that corresponds except at stoich where a range of voltage is appropriate. There was a NB display designed and sold by a couple of Corvette guys that used some extremely fast sampling to generate very close AFR readings even outside stoich. Unfortunately they were temp dependent since voltage on either side of stoich is temp dependent.

.450 is stoich. Stoich represents a balanced AFR where fuel and oxygen react most equally. But stoich changes with different fuel. Same is true with WB sensors. WB displayed AFR isn't right when tuning E100 or other high alcohol fuels. Mixing in "wrong" stuff changes actual fuel delivered at .450V on NB system so E content forces delivered toward richer side.