wideband stoich question

[5_Liter_Eater]

No, changing stoich will make a difference. It tells the computer what the ratio of air to fuel is at stoich (lambda=1) and your PE is a multiplier of that. Your question is somewhat confusing but if you set the stoich to 13 and kept running gasoline the narrow bands would still switch at lambda, which is ~14.7:1 for gasoline. So it would cause your fuel trims to go negative because you are telling the PCM that you are running a fuel that has a stoich of 13 but it doesn't. On the PE side it would show up as artificially low MAF or VE values that would compensate for the discrepancy. you're seeing this now because stoich is set for 14.7 and in reality with the ethanol blend its more like 14.4.

I just read in another thread (sorry, I cant remember the source but he seemed very knowledgable) that while lean=mean with gasoline, E85 is oxygenated and likes to run rich and he suggested .7 lambda for boost and .8 for NA. .7 lambda is a PE of 1.43 (1/.7) and with an ethanol blended gas at 14.4 that is 10:1 (14.4/1.43)! So it doesnt appear that you can switch to lambda tuning and keep the same PE for all fuels. But switching to lambda alleviates the confusion of the wide band reading 14.7 for stoich.

[5_Liter_Eater]

Here is that thread. Pretty good reading. http://www.hptuners.com/forum/showthread.php?t=32501

[thebeewantsboost]

this is almost just a bunch of random rambling. sometimes i think better in text, (this is what goes on in my head!) please comment on it and tell me where i'm wrong and right please.

good read sounds like outside of PE your stoich will just affect your trims. but it makes a big difference in PE. in my head, i'm thinking the narrowbands strive to make the car run at lambda and the voltages some how talk to the computer and populate your fuel trims


its a little confusing to me. how the computer knows what 14.4 is. compared to 14.7.i guess it could be like a wideband where you can program the stoich to whatever you like so lambda 1 is converted it to that number. and it just shifts tables around or something?

the trims are based off the inputted stoich and the actual lambda
if running E10 (14:1) and scheduling a stoich of 14.7(gasoline) the trims will make up the difference and without a scanner you wouldn't be the wiser.
however, you would theoretically be running lean at WOT(PE). its not really a problem because most factory tunes are pig rich for safety reasons. but it shows the importance of tuning your fuel trims.

i don't have my laptop with me. so i'm not sure. but i think i have a PE BASE AFR. and then adder tables. i will confirm that later.
e10 should be alot more like gasoline compared to e85 as far as the lean is mean thing... might just make it a smidge richer.

[5_Liter_Eater]

The effect of having stoich wrong is the same in open and closed loop. The result is you end up running richer or leaner than expected. Its just that in closed loop the trims take care of it. You would end up tuning the discrepancy out of the open loop cells so net net not a huge deal but if stoich is off by a lot then you're artificially lowering or raising airflow to make up for the difference and on an auto tranny that uses calculated TQ to determine shifting techniques (A6) that could end up bad.

Narrow bands just tell the PCM whether the exhaust gasses are leaner or richer than stoich. If its richer then the PCM decreases fuel trims to account for it and if its leaner it increases fuel trims. This happens very quickly with short term fuel trims. If a short term trim stays positive or negative for a certain time the PCM adds or subtracts that to/from the long term fuel trim. So STFT is -5 for 10 counts; PCM Sets the LTFT for that fuel trim cell to -5 and resets the STFT to 0. Then you will see the STFT go positive, negative, positive as the narrow bands report too rich, the STFT compensates, the narrow band reports too rich, the STFT compensates.

The car knows there is a certain amount of air being ingested and it knows stoich based on what you tell it so it determines how much fuel to put in. It also bases how much extra fuel to add when you command a richer EQ ratio in PE based off of the stoich and measured (MAF) or calculated (VE) airflow.


You should enter your knowns (injector flow and stoich) so you can tune to an accurate airflow number. The problem becomes some widebands being hard coded to show stoich as 14.7 which makes things rather confusing. Thats why you tune in terms of lambda. Either that or just live with the fact that lambda is really ~14.4 and your wide band thinks its 14.7.

I'm switching to an Innovate MTX-L soon. I know you can tell it what stoich is but I think it's just a dropdown for different fuels so I may still be stuck with 14.7.

[thebeewantsboost]

do narrowbands look for your commanded stoich? or just actual lambda?

[5_Liter_Eater]

Lambda

[thebeewantsboost]

do you think you could share a config file with me, it doesn't need to be for an aem wideband. there are just a few things as far as the pids go that i'm unsure of how to do, and it would be tremendously helpful. thanx

[5_Liter_Eater]

Attached is the config I use normally although it's not set up for lambda. Also here is a good thread on setting up PIDs and histos for lambda tuning.

http://www.hptuners.com/forum/showthread.php?t=34284

[Overkill]

Narrowbands looking for lambda makes sense. The psuedo lean settings and changing stoich never made any difference on my wideband on any vehicle. Disappointing.

[passingpower]

Very disappointing indeed, Will.

[IndyPete]

I've been reading through this and some other threads and I just wanted to clarify something. The narrowbands read Lambda, I got that. Is Lambda a static 14.7 (as far as the O2 sensor is concerned)? Does blended gas where Lambda is 14.4 turn my stock narrowband into reading 14.4 as Lambda?

Here's why I ask:
My LC-1 wideband shows an average of 14.4 at cruise and my LTFTs + LTFTs are +-2 or so.

If I switched to unblended gasoline(hypothetically) would my wideband now show 14.7?

I want to start tuning using my wideband and using lambda but I want to make sure I got this right. Thanks,

Pete

[Kyne]

The wideband is not an AFR sensor, it's a lambda sensor that converts it to AFR by multiplying it by a constant Stoich (14.7 for yours) so if you are getting 14.4 on that gauge you are rich no matter the fuel. That's why you want to tune in only lambda. The gauge will read 14.7 at stoich even if you have e85 in there.

[gtpsleeper]

Indy,

IIRC, also remember a wideband is less accurate in lower rpms so fuel trims and AFRs between the narrowband/wideband might be a little off at cruise/idle rpms. So, its usually a good idea to tune via wideband in a more WOT setting and leaving the lower rpm stuff to the narrowbands. (Someone correct that statement if it is wrong as I cannot find the literature on it right away.)

[Gibby]

You are correct, though wideband can get you a pretty good ballpark figure of idle and cruise stoich, it is always recommended to go back and clean up with a narrowband.