O2 sensor R/L settings...

[BBA]

I thought the O2 sensor R/L vs airflow mode tables did not make any difference on the newer PCMs...so what am I seeing? (2007 TBSS)

I did a few open loop tunes and decided to go back and try some closed loop again and for some reason decided to try what I had tried before...changing the O2 sensor R/L values to 300 mv switching voltage at all but the two high flow cells. Well, guess what...it made a huge difference.

The fisrt thing I noticed was my fuel trims changed...big time. I was used to -3 to 0 STFT's with pretty close to 0 LT's. As soon as I flashed it and drove, I noticed the fuel trims going way negative. The LTFT's are like -10 and the STFT's float between -9 and 0. I did nothing to change my MAF or VE parameters from the way it was before so I am assuming the PCM now thinks it needs to lean out because the lower switching voltage is telling the PCM to reduce fuel.

I did also notice my mileage picked up by about 3 mpg over my open loop lean tune (which wasn't quite right). I am now seeing steady cruise mileage ov 23.5 MPG at 55 MPH and I never saw above 18 MPG at that speed before...never.

So I did some WOT runs, it runs the same as before, no difference in scan logs or anything.

Honestly, I don't even think I want to adjust the MAF to get FT's down close to 0, because if I do, I would have to know the new value to substiture in for Stoich to counter the leaner burn, in order that PE will keep at the right level. I guess if I had a wideband to tell me what my cruise AFR is exactly I could set that as teh stoich, then tune MAF to get FT's down, then set PE for the correct WOT AFR...but it just seems easier to leave it this way since I know my PE is fine when in OL.


Thoughts?

[LazMan]

WOW!

I know on my car, stock, the O2 crossovers were 450 ..... 550 575 or something like that at the last few cells. I set them all to 450 and it helped my car slightly. (BTW, the MAF pressure thing for PE helped me a lot!)

However nothing under 450 worked. Ever.

Thats BETTER than my hacks (which have been driving me nuts because of lack of time to invest in it)!

IF that is working, that is precisely how its supposed to be and how it was in Gen III motors. You adjust at the O2 crossover values that correspond to the airflow rates that you want to run slightly lean, that way if you put a lot of load on, the O2's migrate back to 450. You can then run slightly lean where you want it, manually adjust the timing in those cells a few degrees, and voila! You wouldn't want to adjust your MAF or SD values.

At least thats the theory. That's amazing! Maybe the trick is to set them all to 300 across the board? Maybe its something they did on this latest build? I doesn't know. I've been running closed loop again, but with 450 across the board. Been playing with DOD and Torque Converter pressure and have gotten some gains on-par with my lean settings prior.

One note: When I first went back to closed loop, my fuel trims were WAY negative. I assumed this was because when you run open loop, the canister purge doesn't happen... so fumes accumulate. These fumes may have contributed to my negative fuel trims. Way negative. I assumed that they went away after a few trips, but I have not really had time to scan lately.

So, given my above note, I think a careful analysis is needed. I'll take a scan on the way to work tomorrow with the way my tune is now. Then I'll give changing the O2 values a shot again, and take a scan on the way to work on Monday. That seems like a fair way to compare.

-Laz

[5_Liter_Eater]

Maybe this got fixed in 2.22. That would be nice.

I won't be able to test it for a while as I'm having to swap out head units. The one Paxton "fixed" is still leaking out the compressor side. I need to fix a leak in my front main seal as well...

[Texsrt4]

3mpg...i am going to change out my settings tomorrow in my sierra and see how we do. i will post back here

[LazMan]

BBA, I don't think its working. I think you had the same thing I had with the charcoal canister fumes being so much they were forcing trims negative.

I just did some testing and my fuel trims are no longer negative. However, as for O2 crossover, nothing. Even if I set a straight 300mv, the average crossover at any airflow was around 430-470.

This was with a fully warm car, but out of gear and not moving, just holding the throttle at different airflows. I'm going to give it a try now on the way home and see what I log.

[BBA]

BBA, I don't think its working. I think you had the same thing I had with the charcoal canister fumes being so much they were forcing trims negative.

I just did some testing and my fuel trims are no longer negative. However, as for O2 crossover, nothing. Even if I set a straight 300mv, the average crossover at any airflow was around 430-470.

This was with a fully warm car, but out of gear and not moving, just holding the throttle at different airflows. I'm going to give it a try now on the way home and see what I log.

You may be right, my trims started coming back closer to normal and the mileage gain seemed to go back closer to normal the more I drove it, even after resetting and even after reflashing again.

Maybe there is something to it and from what you say, it might have something to do with settings in the evap systems. You think we can fool the settings a little?

Food for thought.

[LazMan]

I saw a tune that had a setting for how much the EVAP system was on at certain RPM ... I don't remember what vehicle, but it was 2008. Maybe the 2008 Pontiac G8?

[BBA]

I am also wondering if the evap does not start kicking in and effecting FT's until the emmissions test are done...meaning, disable the tests might do the trick.

[BBA]

Ok Lazman...I'm experimenting again. This time with turning off cat/emmissions tests. I think somehow once the test are complete, it uses some other parameters to control O2 switching, making the R/L settings irrelevent.

I will drive it a week to see how it effects anything, since immediately right after flashing you can't tell anything.

[LazMan]

I think somehow once the test are complete, it uses some other parameters to control O2 switching...

Hmm ... you've got an interesting theory, I like it. Good luck!

[Vettepartz]

Is there any chance that the value we put into the Stoich fuel/air ratio might have something to do with the switchpoints for the O2's? I tried the lower 300 vaues also and things seem to slowly come back to that 450 area.

[LazMan]

Thats right Vettepartz. However, changing stoich will knock a LOT of other tables out of whack, and the O2 sensors will still fight for 450mv anyways.

On Gen 3 motors, that table would allow one to set and value, and the PCM would use it at the corresponding airflows. On Gen 4, we are trying to figure out a work-around to allow the use of this table for values less than 450mv.

PS: BBA, my cat knocked down my laptop and broke the screen ... so I'm out of commission for a week or so (stuck running E60 too ... side-experiment ... thank goodness there's a good tune in there and my injectors can go that far!)

[BBA]

Just a side note Laz, I was driving with the closed loop normal tune today and noticed that at idle, if I forced off closed loop, mixture went rich and pegged O2 sensors. This means the lean tune you made did not have an issue, but it's an open loop problem GM has at low engine speeds. I am going to corerct for it by adjusting idle ranges of MAF freq while in open loop for as close to 400 mv as I can in my normal tune.

I may even do a complete MAF tune on it and concentrate on low speed areas.

[Chris@HPTuners]

we haven't added the min/max and a couple of other params yet. It is being worked on right now.

Chris...

[LazMan]

The MAF tune is how I dealt with the same issue, but it got to be ... frustrating. Now I'm stuck getting under 20mpg because of 1. Ethanol and 2. Lead foot. (The ethanol + more aggressive timing = more HP = more flooring it. She's running sweet.)

YAY Chris! Yes, I've always known the min and max are the secret for Gen 4's, not just the crossover. Bill and I could set the max down 50 or 100mv at certain air-flows, bring the crossover down a bit too and ... hello MPG.

Let us know Chris? Lots of us have wanted this for years. I know 5L-Eater has too!