Changing O2 Switchpoints to Match WB

[5_Liter_Eater]

I have my VE pretty much dialed in via WB, could be better but I got a little tired of it. Tuned the MAF in no time (with WB also). I re-enabled closed loop and my average fuel trims ranged from -10.5 to 1.6. What I did was to set up a histogram that plotted the LTFT's against the Closed Loop Mode VS: Airflow table. Then I averaged the numbers that fell into the defined airflow modes and tweaked the switchpoint for that airflow mode accordingly. It seemed to make a difference, trims now ranged from -7 to 7. I need a few more iterations to see if its making a real difference and need to try playing with altering my airflow modes but what I noticed is that after my fuel trims started to settle that my actual AFR was above stoich; it floats back and forth in the 15's. Every now and then a 14 wil pop up but for the most part the AFR was probably ~15.5 in a real steady state cruise condition. That got me to thinking, should I be tweaking the switchpoints to reduce the fuel trims or to obtain as close to stoich or is that even possible? It seems like the narrow band O2's think stoich is ~15.5. Obviously changing the switchpoints will change the fuel trims but will it have an effect on the actual AFR that is achieved?

[EC_Tune]

It will have a slight effect on the fuel trims as you are moving the "average" o2 values that the PCM considers 14.7 AFR up or down. At flat level cruise, I would try to get the AFR up in the mid 15's if you can. It can help fuel economy. Don't worry about going to far as there are limiters in the cal we don't have access to.

[5_Liter_Eater]

OK, if running @ ~15.5 is ideal I won't worry about trying to get it to 14.7. I knew 15 was better for mileage but didn't want to damage anything long term. I'll focus on making the fuel trims jive with my wideband. I posted another thread about whether changing the airflow modes affected anything other than switchpoints, do you know the answer to that Doug?

[EC_Tune]

At light throttle you usually "can't" hurt anything as the cylinder pressure is much lower. At most you can make it feel sluggish at light throttle by running leaner.

[domestic rice]

So 5 LE how did this work for you? I am going to try to get mine to match up this week. Any tips/tricks on how to get it right?

[5_Liter_Eater]

It didn't work. Changing the switchpoints did nothing on my PCM. Chris mentioned in another thread that there were internal limits preventing the changes from taking on the LS2 PCM's and they would be removed in a later release.

[Alvin]

I have done this with great success on the old LT1 computers. I could taylor my switch points to hit any reasonable AFR I wanted. I took alot of dataloging and you should do an uncertainty anaylsis on your WB vs NB results to get a feel for how accurate you can be.

[domestic rice]

It didn't work. Changing the switchpoints did nothing on my PCM. Chris mentioned in another thread that there were internal limits preventing the changes from taking on the LS2 PCM's and they would be removed in a later release.

It didnt work for the LS2 or it wont work b/c of the HPT? I have an LS1 will it have any effect on mine? Why would HPT put that adjustment in there if it doesnot do anything?

[5_Liter_Eater]

Pretty sure changing the switchpoints on the LS1's has some effect.

[SSUte01]

Yep in LS1s I have had a fair old fiddle and it definitely has a positive effect at saving some fuel in various airflow modes, didnt try and find the limits though

[domestic rice]

Yep in LS1s I have had a fair old fiddle and it definitely has a positive effect at saving some fuel in various airflow modes, didnt try and find the limits though

So what way would it need the switch points to go? My ltft's are well into the -'s and my stft's are +1 or +2, but my wb is dead on.

[5_Liter_Eater]

It gets pretty complicated. The O2 switchpoints are based off of airflow mode (O2 rich/lean VS: airflow mode). The airflow modes are based on mass airflow (mode VS: Airflow). So you would plot LTFT against the airflow table and then set up the airflow modes to follow the regions of fuel trims. Then play with the switchpoints for the airflow modes. It won't be a copy and paste %. So if you have a region of +5 LTFT and define an airflow mode for it you couldn't just multiply that mode's switchpoint by 95%, you'll have to play with it and see what kind of multiplier you would need.

[domestic rice]

I cant figure the switch point out at all. I just added 25 to all the switchpoints and it did not appear to do a thing??? Any Ideas?

[5_Liter_Eater]

25 is a very small amount for the switchpoint. Try adding ~150 or so just to see if it has an effect.

[domestic rice]

I am going the right way here by adding correct? My WOT is around 960 and I want it to be around 800, I think.?.?.?

[5_Liter_Eater]

The way to do it is to set up a histogram like #8 in the attached config. It plots the O2 mV against the airflow table when the WB AFR is between 14.65 and 14.75. Then, drive around and log data. When you're done you should see some pretty defined bands/regions of similar numbers. Use these bands to re-do your closed loop mode VS: airflow table so it matches. The #'s for the airflow modes are arbitrary, they just define modes (0,8,16,24,32,40,48,56,64) and don't represent anything more. Use one of these numbers for each region. Then take the average for that region and plug it into the corresponding switchpoint airflow mode.

So you log data and find that between 12 g/sec and 32 g/sec your O2's are ~600mV (+ or - ~50) at stoich. So put 8's in the closed loop mode VS: airflow table for cells 12, 16,20 and 24 and then put 600 in the mode 8 switchpoint for both banks.

[domestic rice]

The way to do it is to set up a histogram like #8 in the attached config. It plots the O2 mV against the airflow table when the WB AFR is between 14.65 and 14.75. Then, drive around and log data. When you're done you should see some pretty defined bands/regions of similar numbers. Use these bands to re-do your closed loop mode VS: airflow table so it matches. The #'s for the airflow modes are arbitrary, they just define modes (0,8,16,24,32,40,48,56,64) and don't represent anything more. Use one of these numbers for each region. Then take the average for that region and plug it into the corresponding switchpoint airflow mode.

So you log data and find that between 12 g/sec and 32 g/sec your O2's are ~600mV (+ or - ~50) at stoich. So put 8's in the closed loop mode VS: airflow table for cells 12, 16,20 and 24 and then put 600 in the mode 8 switchpoint for both banks.

No clue what language that was in but you lost me after the first line. I just added 150 to all the switch points and it appears to have brought them closer to 0, making my WB line up a litte better with everything else. I will run it like this for a while and see how it goes.

Thanks for the help man, and I will look into this a little more and figure out what you are saying to do.

[Texsrt4]

hey 5, i wouldnt worry about a 15.5 afr under light loads, if anything it will make the car get better mileage, and it will help clean your plugs a bit too. i have tuned cars that ran 16.5 or even higher AFR's while cruising...though thats not quite legal or advised on your average street car.

[5_Liter_Eater]

Histo 8 in the above config plots the O2 voltages against the airflow table when the WB AFR is between 14.65 and 14.75. So you can see from the attached screenshot of a recent log of mine that my narrow bands are well into the 700's when the WB is readign ~stoich. Now if you look at the fuel control, open loop, general, mode VS airflow table you can see the same airflow table and it specifies airflow modes for each flow #. If you go into the switchpoint tables you see that you can define the stoich AFR mV for these dfferent airflow modes. So you should re-define the airflow modes to match up with 'ranges' from your log. It's a little subjective but in my log I would define flow from 0-12 g/s as airflow mode 0, 16-60 g/s as airflow mode 8 (which is the next possible airflow mode), 64-72 g/s as airflow mode 16, 76-88 as mode 24 and so on. If yo look at my screenshot you can see how I defined band of similar O2 mV as airflow modes. Then I would take the average of the airflow modes that I defined and make that my stoich mV value for that range. So for airflow mode 0 I would average 739, 714 and 699 and get 717 and put that as my mV value for airflow mode 0 in the swithpoint table.

I might add that this is all theoretical and I haven't been able to prove that it works since changing the switchpoints on a 4th gen has no effect. This will only work on a 3rd gen.

[5_Liter_Eater]

hey 5, i wouldnt worry about a 15.5 afr under light loads, if anything it will make the car get better mileage, and it will help clean your plugs a bit too. i have tuned cars that ran 16.5 or even higher AFR's while cruising...though thats not quite legal or advised on your average street car.

I'm not so much worried about cruising aroung at 15.5:1 but my concern is whether or not the WB is correct or not, across the whole AFR range. Using this method assumes that the WB is correct and calibrates the narrow bands to agree with the wide band.