Running Flex Fuel on Stock 2019 GT – Wondering if stock fuel system can safely handle E85/93 mix, if flex kit is needed, and if 93-only tanks is fine

[Lucas_M19GT]

Hey everyone, new member here!

I have a 2019 Mustang GT with a Roush cold air intake, and I just ordered a Level 3 tune from Ortiz Performance. The tune supports flex fuel, and I’d really like to run E85, 93 octane, or any mix of the two depending on availability.
However, I’m a bit concerned about whether my stock fuel system can safely handle E85 or flex-fuel mixes without any mechanical issues. Specifically:

1. Do I need to install a dedicated flex fuel kit (like a sensor) to run flex fuel reliably, or is the stock fuel system + tune alone enough?
   
   
2. I’ve been looking at the Burger Motorsports Bluetooth Flex Fuel Kit for the 2015-2023 Mustang GT. Does anyone have experience with it? Is it reliable and worth installing, or would you recommend something else?

To be clear, I’d prefer to keep the car mostly stock besides the tune and CAI, also I always want to have the option to have a full tank of 93 octane—no big fuel system upgrades (Burger Motorsports Bluetooth Flex Fuel Kit) or extra mods if possible.

Appreciate any advice or personal experiences you guys can share. Thanks in advance!

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[robvas]

I have a 2019 Mustang GT with a Roush cold air intake, and I just ordered a Level 3 tune from Ortiz Performance. The tune supports flex fuel, and I’d really like to run E85, 93 octane, or any mix of the two depending on availability.
However, I’m a bit concerned about whether my stock fuel system can safely handle E85 or flex-fuel mixes without any mechanical issues. Specifically:

1. Do I need to install a dedicated flex fuel kit (like a sensor) to run flex fuel reliably, or is the stock fuel system + tune alone enough?
   
   
2. I’ve been looking at the Burger Motorsports Bluetooth Flex Fuel Kit for the 2015-2023 Mustang GT. Does anyone have experience with it? Is it reliable and worth installing, or would you recommend something else?

To be clear, I’d prefer to keep the car mostly stock besides the tune and CAI, also I always want to have the option to have a full tank of 93 octane—no big fuel system upgrades (Burger Motorsports Bluetooth Flex Fuel Kit) or extra mods if possible.

These are good questions for your tuner. You can do this in a few different ways.

Most people run E85 with just a tune and no other upgrades on a 2018+

 

[Mikepol2]

Running flex with zero issues, no supporting mods. No need for a sensor.

 

[Lucas_M19GT]

Thank you i will contact my tuner, but I will probably run e85 when I tune it.

 

[Pistol_91]

Thank you i will contact my tuner, but I will probably run e85 when I tune it.

Better option than Flex.

 

[engineermike]

Hope Ortiz is using Pcmtec.

 

[Mikepol2]

Thank you i will contact my tuner, but I will probably run e85 when I tune it.

Better option than Flex.

Yep E85 definitely makes more power. Only problem is where to get it and having to test each tank. The EPA website for finding it lists "E85" but the fuel at the listed stations near me is only flex, I have yet to find one that actually sells E85.

https://afdc.energy.gov/fuels/ethanol-locations#/find/nearest?fuel=E85

If you want to buy a 54 gallon drum and deal with storing a bomb in your garage you can do it, for the low price of around $8.50 per gallon:

https://petroleumservicecompany.com...bkDGDWH8NdZtH9IWAJYXErx6S_Q1GYXENTEjVRFKdpVS3

 

[robvas]

If you want to buy a 54 gallon drum and deal with storing a bomb in your garage you can do it, for the low price of around $8.50 per gallon:

https://petroleumservicecompany.com...bkDGDWH8NdZtH9IWAJYXErx6S_Q1GYXENTEjVRFKdpVS3

You could also buy a plastic drum and a pump, or those 5-10 gallon fuel jugs and fill up wherever

 

[MidnightStars]

As Mikepol2 said, E85 will make the most power. But if your tune is specifically for E85, you have to be diligent in testing the fuel everytime you fill up, and adjust as necessary to make sure it meets that E85 octane rating. Otherwise, your car is going to have a very bad time. That YouTuber "itsjusta6" or something did not test it a few times, and that led to him damaging a custom motor he had for his Mustang.

I would stick with FlexFuel for your daily drives, but E85 for those times you can test & use that power.

 

[Lucas_M19GT]

As Mikepol2 said, E85 will make the most power. But if your tune is specifically for E85, you have to be diligent in testing the fuel everytime you fill up, and adjust as necessary to make sure it meets that E85 octane rating. Otherwise, your car is going to have a very bad time. That YouTuber "itsjusta6" or something did not test it a few times, and that led to him damaging a custom motor he had for his Mustang.

I would stick with FlexFuel for your daily drives, but E85 for those times you can test & use that power.

My tune is a flex fuel tune, but my worry is if my stock fuel system can handle e85 either a full tank or mixed with 93 octane, while also being able to just drive on 93 octane.

 

[mejohn50]

Something I don’t understand is why the dedicated E85 tunes allegedly make more power than a flex fuel tune on E85. No matter which way the flex fuel system is setup, OEM inferred logic or PCMTEC sensor logic, the tune can be calibrated to be just as aggressive on E85 as a dedicated E85 tune. My flex fuel tunes, NA and boosted, are setup to allow max timing as low as 65-70% ethanol and I’m using the same timing tables I’d run on a dedicated E85 tune.

 

[MidnightStars]

Something I don’t understand is why the dedicated E85 tunes allegedly make more power than a flex fuel tune on E85. No matter which way the flex fuel system is setup, OEM inferred logic or PCMTEC sensor logic, the tune can be calibrated to be just as aggressive on E85 as a dedicated E85 tune. My flex fuel tunes, NA and boosted, are setup to allow max timing as low as 65-70% ethanol and I’m using the same timing tables I’d run on a dedicated E85 tune.

Correct me if I'm wrong, but FlexFuel tunes aren't pinpoint perfect. E85 tunes is essentially a FlexFuel tuned, but extremely narrowed down to an extremely tight range. Any deviation will cause performance issues.

https://www.mustang6g.com/forums/threads/flex-fuel-tune-vs-e85-only-tune.81922/

I assume when the computer isn't looking for variation in the fuel's ethanol content, it doesn't have to be ready to adjust timing and what not, and can straight believe it's E85 and GO GO GO!

 

[NGOT8R]

I’ve been running three of my four tunes (Flex, E85R and E85 Nitrous) repeatedly on my 2019 Bullitt over the past 4 1/2 years, without any tune related issues. I lived on the Flex tune most of the time and would test the fuel at the pump and/or just watch my nGauge to see what the ethanol content was. They don’t make the nGauge anymore, but there are people selling used ones all of the time.

I eventually had my fair share of fueling issues (blown fuel line and a bad fuel pump), but overall, the car has really liked being on E85. I mention the fueling issues because they’re a real possibility. I made some threads about my experiences in these areas and what I did to correct them if you’d like to search and read up on them.

Overall, I think you’ll be happy with the Flex tune should you get one, but I wouldn’t limit myself to the Flex only, I’d also get the 91-93 and E85R tunes as well, as there usually isn’t an additional charge to do them all.

 

[mejohn50]

Correct me if I'm wrong, but FlexFuel tunes aren't pinpoint perfect. E85 tunes is essentially a FlexFuel tuned, but extremely narrowed down to an extremely tight range. Any deviation will cause performance issues.

https://www.mustang6g.com/forums/threads/flex-fuel-tune-vs-e85-only-tune.81922/

I’m not going to get into a diatribe about how this all works behind the scenes, but if the MBT spark tables are accurate and the flex fuel logic is calibrated correctly, there’s absolutely no reason a flex fuel tune can’t be just as aggressive as a dedicated E85 tune. My statement was more of a bit of disappointment about the state of “professional” tuning on this platform.

What the tuners are doing and what can be done, especially on the gen 3, are two different things. That’s all I’m saying and it’s a little disappointing.

 

[NGOT8R]

I’m not going to get into a diatribe about how this all works behind the scenes, but if the MBT spark tables are accurate and the flex fuel logic is calibrated correctly, there’s absolutely no reason a flex fuel tune can’t be just as aggressive as a dedicated E85 tune. My statement was more of a bit of disappointment about the state of “professional” tuning on this platform.

What the tuners are doing and what can be done, especially on the gen 3, are two different things. That’s all I’m saying and it’s a little disappointing.

I know exactly what you’re talking about. I was told that my Flex tune will still allow timing to function normally, whereas the E85R tune locks timing in and it’s up to the end user to verify proper ethanol content before sending it, in order to prevent bad things from happening.

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