E85 Confusion

[Rush]

I seem to be getting some confusing info from various forum postings and other internet sources about tuning for E85. First of all I’ve seen postings that state that the stoichiometric ratio of gas and E85 are the same; the stoichiometric ratio of any fuel is a lambda of 1, but E85 and gas occur at different AFRs. Stoichiometric ratio is described as the AFR at which the lowest gas byproducts are produced, for gas it is 14.7:1 and E85 is 9.87:1, even with the 30% oxygenation of E85, or 12.83:1, that still isn’t close to 14.7:1 of gas. So it seems to me that if you’re running in closed loop with a narrowband O2 sensor you’re going to be running about 13% lean; so from what I understand whatever your fuel trims are at before going into open-loop or PE is what will be added or subtracted to your commanded AFR. I’ve also seen postings that say an O2 sensor doesn’t care about what fuel you’re running just about how much oxygen is in the air, which is true; but a narrowband O2 for gas is set to switch on/off at an AFR of 14.7:1; some postings make it sound like a narrowband O2 will always be 14.7:1 at the stoichiometric of gas for any ethanol mixture. Maybe someone with some knowledge of tuning for E85 can clarify all of this?

[articzap]

Let me start off by saying that all oxygen sensors read in Lambda. Once you figure out lambda, AFR means absolutely nothing. Lambda reading of 1 will always = stoich for any fuel.

[Rush]

Yes, but a narrowband O2 sensor switches at a lambda for gas and not E85 or any other blend; my LC1 wideband can be configured for various types of fuel which I believe changes the lambda point. I see some postings that say to use your narrowband O2 set for gas, which would cause your car to run lean on E85 and closed-loop.

[wyochimneysweep]

No lambda is lambda and narrow bands work fine on e85.

[wyochimneysweep]

If you change stoich in the tune for e85 then the computer knows what it's trying to hit and the o2 will switch at lamdba of the fuel. Doesn't matter if it's e10 or e40 or e85 they will switch at lamdba for all of them

[Rush]

I noticed this while in open-loop, but in closed-loop it looks like it is trying to do lambda for gas still. I'll have to do some more testing I think.

[5_Liter_Eater]

Stoich is different for E85 and gasoline. But whatever the fuel's stoich ratio is, is lambda 1. So 14.7:1 on gas is lambda 1 and 9.76:1 on E85 is lambda 1. Both narrow bands and wide bands are really reading lambda. The confusion comes in because most wide bands are going to display AFR in terms of gas, so they display lambda 1 as 14.7:1. So if you run E85 the narrow bands are going to try to get you to 9.76:1, which is lambda 1 for E85, but the wide band is reporting 14.7 because it's configured to report lambda 1 as 14.7. Some wide bands let you configure what stoich is and if thats not an option then some others will allow you to display the air fuel ratio in terms of lambda which aleviates the confusion.

[jcrumpley]

What 5 Liter said. This is why I switched to tuning with lambda readings on my wideband instead of AFR. It greatly simplifies stuff.

[wyochimneysweep]

Yep my wideband is configured to lambda also

[Rush]

Well that all makes sense, so because my LC1 is configured for gas it converts lambda 1 to 14.7 AFR, so if I were to configure it for E85 then it would read about an AFR of 9 at lambda.
My big question now is how to get HPTuners to read the same output as the LC1 when it is configured for lambda and not AFR?

[Iam Broke]

Scale a custom PID from your gasoline numbers where 14.7= stoich. Lambda = 1/AFR

Hopefully you know the V output vs AFR already.

[Rush]

I think I figured it out for my LC1, based on HPTuners values they use for an LC1; basically a custum PID for EIO1 V/2.443+0, would give me an output of 1 at gas 14.7. If I'm not mistaken.

[Rush]

After calculating some values I see that this isn't going to work; I had to do a custum PID using a list instead; here are the values I used if anyone is interested:
0.0,0.501
0.1,0.521
0.2,0.542
0.3,0.562
0.4,0.583
0.5,0.603
0.6,0.624
0.7,0.644
0.8,0.665
0.9,0.685
1.0,0.706
1.1,0.726
1.2,0.747
1.3,0.767
1.4,0.788
1.5,0.808
1.6,0.829
1.7,0.849
1.8,0.870
1.9,0.890
2.0,0.910
2.1,0.931
2.2,0.951
2.3,0.972
2.4,0.992
2.5,1.013
2.6,1.033
2.7,1.054
2.8,1.074
2.9,1.095
3.0,1.115
3.1,1.136
3.2,1.156
3.3,1.177
3.4,1.197
3.5,1.218
3.6,1.238
3.7,1.259
3.8,1.279
3.9,1.300
4.0,1.320
4.1,1.341
4.2,1.361
4.3,1.382
4.4,1.402
4.5,1.423
4.6,1.443
4.7,1.464
4.8,1.484
4.9,1.505
5.0,1.525