Stoich and narrowbands

[streetsweepergto]

Let's say I'm tuning with a stoich of 14.69, yet my fuel has up too 10 percent ethanol.

Let's say my ve table is dialed in for 14.69 using a wideband.

Now flip on fuel trims and it says I am lean.

Specifically stft.

Now let's say I retune that ve table with stft and it gives me an avg of 5% lean.

I add it in.

Now did I effectively burn my incorrect stoich value into my ve table?

So obviously the correct thing would be to either set the correct stoich point from the beginning then retune.

But what I don't get is how can you tune with narrow bands that are looking for a stoich point richer then the calibration's set stoich.

If I tuned with a wideband got 0 percent flipped on my stft and was 5 percent lean, then my stoich I should change by 5 percent and boom I should be 0 percent again.

If you don't change the stoich value and your stft keeps showing you 5 percent you would either ruin your part throttle ve work or it will burn in your stoich.

So what is the correct way?

Determine the exact fuel?
How ?
Up to 10% is just too undescript.

[5_Liter_Eater]

You should set stoich to whatever your fuel is. That will vary from tank to tank, especially with E85 but nothing you can do about it. Narrow bands and wide bands are not targeting any AFR but lambda=1, regardless of the fuel. You need to make sure your WB thinks stoich is the same AFR as the tune. Better yet, tune in terms of Lambda. Most WB's are hard coded to convert lambda=1 to 14.7 (NGK AFX is 14.62 I think) so it can get very confusing unless you tune in lambda.

[LSX378]

10% ethanol > why worry. You can mess with your stoich table every time you change the mix but if your STFT will drive your LTFT so that the mix will run at stoich irrespective of fuel fill its all done for you.

Let's say I'm tuning with a stoich of 14.69, yet my fuel has up too 10 percent ethanol.

Let's say my ve table is dialed in for 14.69 using a wideband.

Now flip on fuel trims and it says I am lean.

Specifically stft.

Now let's say I retune that ve table with stft and it gives me an avg of 5% lean.

I add it in.

Now did I effectively burn my incorrect stoich value into my ve table?

So obviously the correct thing would be to either set the correct stoich point from the beginning then retune.

But what I don't get is how can you tune with narrow bands that are looking for a stoich point richer then the calibration's set stoich.

If I tuned with a wideband got 0 percent flipped on my stft and was 5 percent lean, then my stoich I should change by 5 percent and boom I should be 0 percent again.

If you don't change the stoich value and your stft keeps showing you 5 percent you would either ruin your part throttle ve work or it will burn in your stoich.

So what is the correct way?

Determine the exact fuel?
How ?
Up to 10% is just too undescript.

[Mez]

VE is air flow or your engines air pump efficiency prediction. Stoich is fuel to air ratio. Don't mix the two up since Stoich has no affect on your air flow.

Set your stoich to the fuel you are using. In our region, gas pumps are all labeled "up to 10% ethanol", we set stoich to 14.30 which is 7% ethanol. Unless you test each tank, this is close enough.

[streetsweepergto]

thanks guys

i think the question i should be asking is

what is the point of the stoich table in the e40pcm?

so if its e85 fuel then your o2's just do what they need to do to get 1 lambda.
regardless of its stoich setting.


im sure the vehicle that have flex fuel is where that table comes into play by percentage of alchohol.

[Mez]

thanks guys

i think the question i should be asking is

what is the point of the stoich table in the e40pcm?

so if its e85 fuel then your o2's just do what they need to do to get 1 lambda.
regardless of its stoich setting.


im sure the vehicle that have flex fuel is where that table comes into play by percentage of alchohol.

E40 does not have the provision for ethanol.

Technically you are correct. Fuel trims are there for correction based on NBo2 feedback. Stoich is there to establish the a/f ratio to enable a minimum correction. However, the range of correction is limited to 25%.

If you set stoich to the correct fuel in the tank, the PCM standard tables will be closer to the correct a/f ratio, thus less correction will be needed Remember....the O2's are down stream and it takes a few crank pulses to get the feedback and for the PCM to calculate and put the new LTFT correction in play.

[5_Liter_Eater]

The point of stoich is to allow the computer to calculate how much fuel to put in for a given airflow. So if it doesnt match the fuel in the tank then fuel trims will be off, but you'll end up correcting them in the VE or MAF table.

Like I said though, your WB needs to be configured for the same stoich point as in the tune. If thats not possible then you should tune in terms of lambda or set stoich in the tune to match the wide band assuming you're still running E~10 and live with the inherent error that will get tuned out anyway.