What would happen if you put in 6gallons of E85 and 6gallons of 91octane in a stock GT, no mods.

[Racinjason65]

If you have to save up for a tune, you Probably shouldn’t take the risk of hurting your engine by running fuel/mixtures that the car isn’t tuned or originally designed for. If you want to run e85 or a blend, get a tune for that.

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[Dave2013M3]

My baseless and unreliable gut instinct tells me that modern Fords can run up to E20 on stock programming. 50/50 assuming true 85% EtOH would be a lot more than 20%.

That said, take one for the Mustang Team and let us know the result

Actually I have been told it was up to E30. I run E20 with no issues. That mix is E48 or basically E50, you will have issues.

 

[Dave2013M3]

I've done 4 gallons of e85 with 12 gallons of e10. I didn't get any lights but I did not like the fuel trims.

I agree I only run 2.5 gallons with 2 gallon of VP101 street blaze. This gets me to an E22 at 94 octane. You have a 2017 so it would be even more sensitive on the fuel trims.

 

[sgtsabai]

GT Premium, no performance pack, not available here. I have a problem over here in Thailand. There is no real gasoline, just gasohol. I have 91 in tank at present will put 95 in Tue. before leaving for Lao. No! Stang is not going to Lao, stays in Nong Khai. So far with the 91 no problems and performance seems to have improved although I've still got aways to go before complete break in. Then I can see what it will do. When the new cold air filter arrives the car will receive a complete tune.

 

[junits15]

I can answer this:
The short answer is that you will not break anything, the fuel trims will take up the slack until you switch back to regular gas. You may experience weirdness when cold starting but that is basically it.

The long answer:
The primary concern with running ethanol is making sure that you are injecting more fuel than you would be with gasoline. Ethanol needs to be run significantly richer than gasoline. On older narrowband O2 sensor cars running ethanol without a tune could be a death sentence. On this car however we have a lambda sensor, which measures combustion completeness and is agnostic of fuel. So it doesn't matter what fuel you run, the ECM will never allow the car to run lean. It does this by taking the data from the lambda sensor and adjusting the LTFT's to compensate. So when you run ethanol on the stock tune you will see very high LTFT's, don't be surprised if they go into the +30% range as ethanol needs approximately 30% more fuel mass than gasoline at any given point.

The only issue is that there is an upper limit on how much LTFT the ECM can apply before tripping the MIL. If it doesn't know its running ethanol it will assume the additional fuel mass is being caused by a component failure and set the code. Its not dangerous, as there is enough headroom in the fuel system on a Gen 3 motor to accommodate e85. Its just a matter of if the extra fuel is being commanded by the base stoic value or by fuel trims.

We can be confident that it is safe by looking at the stock flex fuel logic from the F150, which is the same motor. All it does is watch for STFT's, if they go above or below a set value, the ECM assumes there is ethanol in the fuel and changes the base fueling. It just repeats this until the STFT's are in a desired range.

Additionally when ruining a flex tune there are cranking fuel and timing tables that are changed, without changing those the car may struggle to start from cold as it will be injecting fuel mass and adding timing that would be appropriate for gasoline.

Its not really worth it to do without a tune, you can get the exact same performance by running octane booster or unleaded race gas and not have to send your fuel trims out of whack or make the car struggle to start. The car wasn't really intended to run like this, you're gaining nothing and pushing the motor into an undefined state.

 

[Cory S]

I can answer this:
The short answer is that you will not break anything, the fuel trims will take up the slack until you switch back to regular gas. You may experience weirdness when cold starting but that is basically it.

The long answer:
The primary concern with running ethanol is making sure that you are injecting more fuel than you would be with gasoline. Ethanol needs to be run significantly richer than gasoline. On older narrowband O2 sensor cars running ethanol without a tune could be a death sentence. On this car however we have a lambda sensor, which measures combustion completeness and is agnostic of fuel. So it doesn't matter what fuel you run, the ECM will never allow the car to run lean. It does this by taking the data from the lambda sensor and adjusting the LTFT's to compensate. So when you run ethanol on the stock tune you will see very high LTFT's, don't be surprised if they go into the +30% range as ethanol needs approximately 30% more fuel mass than gasoline at any given point.

The only issue is that there is an upper limit on how much LTFT the ECM can apply before tripping the MIL. If it doesn't know its running ethanol it will assume the additional fuel mass is being caused by a component failure and set the code. Its not dangerous, as there is enough headroom in the fuel system on a Gen 3 motor to accommodate e85. Its just a matter of if the extra fuel is being commanded by the base stoic value or by fuel trims.

We can be confident that it is safe by looking at the stock flex fuel logic from the F150, which is the same motor. All it does is watch for LTFT's, if they go above or below a set value, the ECM assumes there is ethanol in the fuel and changes the base fueling. It just repeats this until the LTFT's are in a desired range.

Additionally when ruining a flex tune there are cranking fuel and timing tables that are changed, without changing those the car may struggle to start from cold as it will be injecting fuel mass and adding timing that would be appropriate for gasoline.

Its not really worth it to do without a tune, you can get the exact same performance by running octane booster or unleaded race gas and not have to send your fuel trims out of whack or make the car struggle to start. The car wasn't really intended to run like this, you're gaining nothing and pushing the motor into an undefined state.

All
Good and accurate, except I think you meant STFT’s…….

 

[junits15]

All
Good and accurate, except I think you meant STFT’s…….

You are correct, LTFT's will be large on a non-flex tune but flex tunes will initially use STFT's, leaving LTFT's at 0 until the ethanol value matures. Then the LTFT's will kick on. I'll fix my original response.

 

[Cory S]

From what I saw in my own testing, it was LTFT's that really got high, the STFT's tend to stay at small numbers.

Short term trims are immediate and in use 100% real-time. Long term is average adjustment for part throttle over time. I don’t even enable LTFT’s. They are inactive. Many tuning practices disable them for non emissions calibrations.

 

[junits15]

Short term trims are immediate and in use 100% real-time. Long term is average adjustment for part throttle over time. I don’t even enable LTFT’s. They are inactive. Many tuning practices disable them for non emissions calibrations.

Yes, but the way they work is that the part of the fuel trim that is changing is in the STFT and the part of the trim that isn't is in the LTFT. LTFT's change in under a few seconds. On a stock car you'll see large LTFT's

If you have an offset that is wavering between +33% and +40% the STFT will be between 0% and +7% and the LTFT will be +33%

 

[ZXMustang]

Short term trims are immediate and in use 100% real-time. Long term is average adjustment for part throttle over time. I don’t even enable LTFT’s. They are inactive. Many tuning practices disable them for non emissions calibrations.

The best LT tuners do this as well.

 

[Cory S]

The best LT tuners do this as well.

Yep. LTFT is fine long term trim tuning. STFT is all that truly matters in most cases.

 

[PaddyPrix]

... but why? The technology is there for flex vehicles, but yet, the Mustang isn't one, at least from the factory. The gas stoich is 14.7:1, and the e85 is 9.85:1, and having it at some random point in-between those two with the stock computer's logic won't really do you much good. That story changes should you get a tune which allows your tuner to tell the car to perform differently and take further advantage of the higher octane rating and cooling it provides. I'm likely moving out to your neck of the woods, and doesn't look like there's much e85 out there, certainly not the year-round quality we've got here in SoCal.

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