Switching from e85 to flex tune issues

[Jhonda]

I’m having an issue switching from the E85r tune to the flex tune. The car won’t hardly run at all on the flex tune spudders and cuts off. But if I put the E 85r tune and I have no issues. I contacted Jon at Lund and he said I needed to run it down to empty and put some 93 in it and try to keep it running until it learned the new fuel. I have switched back and forth a few times but never had this issue. I just don’t want to end up putting 93 in it and it not work.
Has anyone had this issue?

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[Jhonda]

Best I can get is e70

 

[GreenS550]

He said it's not running right on the flex tune.

I didn't like Lund's flex tune. No real issues, just didn't run very good. The dedicated 85 was very powerful. My recommendation is only use their e85 and when you get near empty put their 93 tune back on and vice versa.

This is just my experience.

 

[Jhonda]

2018 39000 miles

 

[Jhonda]

I will change it but Wouldn’t I have more issues on e85 due to running more fuel through it?

 

[LOL WUT]

I had the same issue coming off the E85R tune. It was explained to me that with straight E85 still in the tank and no new fuel added, a switch from E85R to flex will struggle to start.

The switch from E85R to flex with no change in fuel level leaves the car with a flex tune expecting to learn E content starting low and ramping up. However upon start the E content is much higher than the tune initially expects. After a few failed starts mine came to life and settled down without issue. Lund validated this when I reached out.

 

[Jhonda]

Awesome thanks

 

[LOL WUT]

Awesome thanks

I originally posted about it at the link below.
https://www.mustang6g.com/forums/th...-e85r-to-flex-for-winter.151187/#post-3084219

Seems uncommon as I think most people swap tunes directly after or before a fill up. I have only had an issue when I swapped from R to Flex with no change in fuel level.

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