stoich 14.7. why not lambda 1.00? - Third Generation F-Body Message Boards

Ronny · 03-16-2009, 03:31 PM

In my Tunerpro constants there is a value for stoich. I believe it defaulted to 14.7 which is stoich for regular gas. I changed it some time ago to 14.3 for E10 (10% ethanol) thinking that my tune needed to be corrected for the appropriate stoich value for the fuel I was running.

Now I am a bit confused! If the NB02 sensor, in simple terms, is looking at the amount unburned 02 present then why would a setting be required for stoich? Is not the NB going to place the fueling at stoich regardless of fuel? Assuming there is minimal unburned 02 is not stoich is stoich? I thought the ECU adjusts the fueling with feedback at NB02 sensor so that all the fuel is at proper A/F regardless of whether it is reg gas or E10.

Now that being said would not 1.00 lambda be a better way to discuss A/F rather tha, 14.7-14.3- 9.6/1 ???

Now when I read my WB and I see 1.00 I undersatand what I am getting is a mix of 14.3/1.

Now if I understand this correctly if I were to set my "stoich" constant to 14.0/1 I could tune to BLM of 128 and that would be in reality 14.0/1 or .95 lambda. I I believe raising the rich/median/lean swing points 5-10% would be beneficial to place the swing closer to the enrichment desired.

Any misconceptions on my part?

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RBob · 03-16-2009, 05:44 PM

Bunch of good questions, most of all when I talked lambda folks looked at me like I was talking about herding sheep. Kinda' like can you tuna fish, or can you tuna car?

Anyway, the reason the ECM needs an AFR value is that it needs to know the ratio of air to fuel. Lambda doesn't provide that.

The NB and WB O2 sensors read lambda. This is why in the ECM there is a table of O2 values in milli-volts. For a WB there is a conversion done in the controller to provide an AFR value.

With the NB O2 sensor reporting lambda it doesn't care what fuel is used. E0, E10, E85, the NB O2 will report stoich as 450 mV. So if you take your current vehicle and fill it with E85, the BLMs will rise to bring the mix back to stoich. Based just on the NB O2 sensor feedback.

The main reason to change the stoich AFR to 14.2 when running E10 is to make the calibration more accurate. But it sorta' opens another can of worms. Because now the PE mode AFR also needs to be lowered. Along with the lean cruise mode.

For your last statement, it doesn't matter what you set the stoich constant to. The NB O2 feedback along with the INT & BLM will bring the AFR to whatever the O2 windows values are.

As an example, you have the perfect 128/128 with a stoich constant of 14.7:1. You now change the stoich constant to 14.2:1. This increases the injector PW as it is a richer AFR.

In turn the NB O2 feedback will lower the INT and BLM. And the injector PW will in turn end up being the exact same as they were with the stoich value of 14.7:1.

RBob.

Ronny · 03-16-2009, 06:05 PM

Quote: In turn the NB O2 feedback will lower the INT and BLM. And the injector PW will in turn end up being the exact same as they were with the stoich value of 14.7:1.

So the actual CL A/F ratio is controlled by the switch points set in lean-median-rich values so if one increases them 5-10% as I stated it will in fact enrichen the mixure the car will run at? that is what I did trying to achieve a 14.0/1 CL operation slightly richer than E10 stoich. My "stoich" constant is set to 14.0/1 as well. My PE is set to 12.0/1 at the higher RPMs.

RBob · 03-16-2009, 08:28 PM

If you want to run stoich in closed loop then bracket 450 mV with the O2 window:

Lean: 425 mV
Rich: 475 mV

Doesn't matter what the fuel composition is.

RBob.