How intelligent are our ECUs at learning?

[cctman]

An example would be if I am running a stage 3 93 octane build but add in a couple gallons of E85 to a full tank, would the ECU over time learn to increase timing? If so how long?

 

[koozy]

yes. fuel trims can swing +- 30. the learning starts immediately and is constantly adjusting.

 

[cctman]

yes. fuel trims can swing +- 30. the learning starts immediately and is constantly adjusting for optimal state of tune.

OK... I did this exact scenario, and I'm now down to half a tank of fuel on my first go. Shouldn't the ECU have adjusted already and therefore ultimately I should be able to feel a mild difference in torque and hp?

 

[koozy]

Your car will run, but it's not going to run optimally because it's not tuned to really take advantage. Others have done this and experienced the same as you are. I wouldn't put more than 2 gallons to a full tank without a tune to compensate for it.

 

[Hijinx]

More ethanol = different AFR.

 

[BeansNCornbread]

Your car will run, but it's not going to run optimally because it's not tuned to really take advantage. Others have done this and experienced the same as you are. I wouldn't put more than 2 gallons to a full tank without a tune to compensate for it.

+1 on this. I'm on stock and get the same MPG v/straight 91 but get better power delivery and longer boost and RPM benefit. I also feel less a penalty in higher temps if any at all. So, I'm using E85 to get to 93-94AKI.

 

[iso100]

More ethanol = different AFR.

THIS.

It will run, but you'll have reduced power and definitely reduced fuel economy.

I'm running a custom e20 tune and it works great with all the tweaks required to make it work. Just dumping in 1 gallon of e85 to a tank of 93 may be fine to add a few octane points though.

 

[cctman]

THIS.

It will run, but you'll have reduced power and definitely reduced fuel economy.

I'm running a custom e20 tune and it works great with all the tweaks required to make it work. Just dumping in 1 gallon of e85 to a tank of 93 may be fine to add a few octane points though.

Adding a little bit of ethanol to OTS Cobb map will give you "reduced power and definitely reduced fuel economy"? How so?

 

[iso100]

Adding a little bit of ethanol to OTS Cobb map will give you "reduced power and definitely reduced fuel economy"? How so?

"a couple gallons" of e85 added to a tank (you need to add the e85 FIRST before finishing the fill with e10) will likely put you beyond e20 and into the e25 range. If you're running a tune that expects e0 or e10 then it's looking at a stoich target of 13.24 AFR instead of 14.64.

Gasoline has 112,114 BTU/gal while e100 has 76,330 BTU/gal. This, combined with the fact that ethanol needs a richer fuel mixture for proper burn means a non-ethanol tune running e20 or e25 will have slightly less ultimate power and economy.

I usually wait until I'm down to 1/8th tank and add between 1 and 1.5 gallons of e85 before filling with 93 the rest of the way. I have a calculator on my phone that helps determine exactly how much e85 to mix with whatever fuel I'm adding to achieve the desired ethanol percentage. I have an AP monitor that displays fuel level in % and then use that to calculate liters to add.

 

[dyn085]

"a couple gallons" of e85 added to a tank (you need to add the e85 FIRST before finishing the fill with e10) will likely put you beyond e20 and into the e25 range. If you're running a tune that expects e0 or e10 then it's looking at a stoich target of 13.24 AFR instead of 14.64.

Gasoline has 112,114 BTU/gal while e100 has 76,330 BTU/gal. This, combined with the fact that ethanol needs a richer fuel mixture for proper burn means a non-ethanol tune running e20 or e25 will have slightly less ultimate power and economy.

I usually wait until I'm down to 1/8th tank and add between 1 and 1.5 gallons of e85 before filling with 93 the rest of the way. I have a calculator on my phone that helps determine exactly how much e85 to mix with whatever fuel I'm adding to achieve the desired ethanol percentage. I have an AP monitor that displays fuel level in % and then use that to calculate liters to add.

That's all basically irrelevant. The car doesn't care what the stoich rate of the fuel is because it is going to target lambda, and 1 lambda is 1 lambda regardless of what fuel you put in-whether that is straight E85 or E0. This is the benefit of wideband O2 sensors.

Where it matters is in the timing, not the fuel delivery. If your tune is targeting 93E0 and you put straight E85 in then you're going to be dumping a ton of fuel to make .8 lambda (for example) but you're still going to have timing for the 93E0. Basically, your STFT/LTFT are going to skyrocket and your timing is going to stay the same. You're going to have a ton of headroom for timing and not be able to take advantage of it. Theoretically you should end up with roughly the same power despite the use of more fuel and if you're at your KS limit or are already hitting the timing ceiling then that's all you're going to get.

This is why adding a gallon or two can assist on a vehicle that is maybe near the threshold of the tune-it can bump the octane enough to take full advantage of the tune and allow it to hit it's limits while the STFT/LTFT ensures enough extra fuel is delivered. Anything above those limits is just wasted fuel.

Edit: The best economy comes somewhere between E25-E30 iirc. The best power comes from more, obviously.

 

[cctman]

That's all basically irrelevant. The car doesn't care what the stoich rate of the fuel is because it is going to target lambda, and 1 lambda is 1 lambda regardless of what fuel you put in-whether that is straight E85 or E0. This is the benefit of wideband O2 sensors.

Where it matters is in the timing, not the fuel delivery. If your tune is targeting 93E0 and you put straight E85 in then you're going to be dumping a ton of fuel to make .8 lambda (for example) but you're still going to have timing for the 93E0. Basically, your STFT/LTFT are going to skyrocket and your timing is going to stay the same. You're going to have a ton of headroom for timing and not be able to take advantage of it. Theoretically you should end up with roughly the same power despite the use of more fuel and if you're at your KS limit or are already hitting the timing ceiling then that's all you're going to get.

This is why adding a gallon or two can assist on a vehicle that is maybe near the threshold of the tune-it can bump the octane enough to take full advantage of the tune and allow it to hit it's limits while the STFT/LTFT ensures enough extra fuel is delivered. Anything above those limits is just wasted fuel.

Edit: The best economy comes somewhere between E25-E30 iirc. The best power comes from more, obviously.

So if I tune for E20 if I understand correctly that would be 93 octane and roughly 2 gallons of Ethanol per tank. What would be the performance gains? Are they that noticeable over a 93E0 stock tune?

 

[dyn085]

A handy chart-

I don't know what the gains would be as I haven't done any ethanol tuning, but it would be noticeable. I'm sure there's an equation out there, I just don't know it.