Stoich at 14.0

[Widebody06]

So another newbie here, trying to figure out how to improve my idle and general drivability. While looking thru my current tune(done before I got the car) I see Stoich is set at 14.0 across the board, seems it should be 14.69 with declining values as alcohol content increases.
So the questions- any good reason for running 14.0? any reason to have different table values on an '06 GTO LS2? I presume one needs a fuel composition sensor which logic tells me would require a flex fuel rated vehicle to need one.

[mowton]

So another newbie here, trying to figure out how to improve my idle and general drivability. While looking thru my current tune(done before I got the car) I see Stoich is set at 14.0 across the board, seems it should be 14.69 with declining values as alcohol content increases.
So the questions- any good reason for running 14.0? any reason to have different table values on an '06 GTO LS2? I presume one needs a fuel composition sensor which logic tells me would require a flex fuel rated vehicle to need one.

Technically, as we are all running a derivative of E10, the stoich being used today is 14.2. Believe the true stoich vale for pure E10 is like 14.08 and pure gas is 14.68, so they add a bit to compensate for variations in alcohol content....kind of a compromise if you will. That is why we use lambda. Lambda 1.0 is Lambda 1.0 whether it is pure gas, E10, E85 or E67.5.


Ed M

[Widebody06]

Thanks for the explaination, FWIW, there are supposedly 24 gas station in my state selling 100% gasoline, unfortunately none in my town. Guess I should put learning to tune using Lambda on my get another headache list.
Looks like we have pretty similar motors ED M

[08 IOM G8]

mowton,

I'm new to tuning and have searched to death regarding low afr with no clear explanation. My WB reads at 14.2 sitting at an idle and I have been running 10% blend. Since the WB should be reading in lambda and converting to afr, shouldn't the WB still show 14.7? or am I way over thinking this. I've looked at this thinking that something's not right but the voltage on the WB reads 2.98-3.01 V. The vehicle 's a 08 G8GT mostly stock with some exhaust work. I've tried to understand the PIDs for lambda and have just frustrated myself to this point.

[daniel76309]

Disclaimer, I'm not an expert, but this is my understanding...

Yes, I believe your wideband should read ~14.7 regardless of fuel composition.

Just a guess, but perhaps it could be that someone set stoich to be at 14.0 in open loop in order to make sure you have negative fuel trims when running in closed loop. I think I read somewhere that if you have positive long-term fuel trims, this results in fuel being added when in open loop/power enrichment mode, so you end up being richer than you would like to be--however, negative fuel trims have no effect. So, it is better to err on the slightly rich side for your open loop calibration. (All of this assumes that your MAF is calibrated correctly.)

Regarding why your wideband reads 14.2 in closed loop, I had the same problem, but have gotten it to run stoich or even slightly lean in closed loop by playing with the O2 switching voltages. I have had to go all the way down from 450mv at the start to something like 80 before I saw an effect. I am still playing with it, trying to get it to cruise lean and be stoich otherwise.