Engine blipping throttle on each A10 downshift after e85 tune?

[Biggness]

Encountered a weird problem that my tuner or myself can't figure out.

Using HP Tuners, we flashed a flex tune to see how well I would be able to manage running e85 only since there's only three gas stations that carries it in a 50 mile radius.

After about a month, I felt comfortable with going to an e85 only tune.

We flashed that, and did some test hits. Noticeable difference between flex tune and e85 tune performance.

Here's where the problem arose; on the way home, I noticed that with each downshift of the transmission when slowing down, the engine would blip the throttle anywhere from 500-1000rpm with each lower gear shift. Enough to lurch the car forward a few feet while braking. I thought that maybe it was the computer relearning my driving style, but that's not it. I brought it back the next morning, and we did some more test drives. He couldn't find anything. No torque management was changed, no shift patterns, nothing. Even doing the compare feature between the the flex tune and the e85 tune showed nothing but adding in some more timing for the e85 only tune.

So he made me a new file with the flex tune and two extra degrees of timing to replicate the e85 tune, and that's what I'm riding around on now.

Any idea what would be causing this?

If it helps any, we disabled Active Grill Shutter, and added a smidgen of communication delay for the o2 sensors.

Thanks in advance for any help!

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[MCS]

Are you sure this isn't just rev-matching on the downshift? My car does it and I don't have E85.

Did your tune adjust your transmission shift points at all so that things "feel different" to you?

 

[Biggness]

Are you sure this isn't just rev-matching on the downshift? My car does it and I don't have E85.

Did your tune adjust your transmission shift points at all so that things "feel different" to you?

No, it's a HUGE difference between the stock and flex tune rev matching, and the e85 tune. Almost like it's stuck in S Mode instead of D Mode. Way more violent.

 

[engineermike]

Did the OS change or did all the tunes start with the same origin file?

 

[Biggness]

Did the OS change or did all the tunes start with the same origin file?

They all started with the same origin file.

 

[engineermike]

Do you know exactly what was changed in the dedicated e85 tune?

 

[Biggness]

Do you know exactly what was changed in the dedicated e85 tune?

AFAIK, just some more timing is the only difference.

 

[engineermike]

AFAIK, just some more timing is the only difference.

Ok but was it added to the borderline or mbt tables?

 

[Biggness]

Ok but was it added to the borderline or mbt tables?

Flex tune it's added to the flex tables, and e85 only is added to both borderline and mbt tables.

 

[engineermike]

Ok my money says it’s the mbt tables that are the culprit. When the pcm is controlling torque it uses mbt as a baseline to delta off of. If you raise mbt then it lowers calculated torque for a current set of conditions. Since torque is the goal, it will increase timing and/or throttle to get back to the desired torque, but it overshoots since mbt is higher than it should be. Btw if you log it you’ll probably see the torque source is “torque+ from trans”.

 

[engineermike]

If it were me I’d steal the mbt ethanol correction from a flex fuel f150, and apply that directly to the mbt tables. That should keep torque accurate. If you really feel like mbt is set too low then only raise it at 1.1 load. If you must raise it at .85 then only do it at high rpm.

 

[Biggness]

If it were me I’d steal the mbt ethanol correction from a flex fuel f150, and apply that directly to the mbt tables. That should keep torque accurate. If you really feel like mbt is set too low then only raise it at 1.1 load. If you must raise it at .85 then only do it at high rpm.

Thanks for the suggestions.

I relayed what you said to my tuner, his response was:

"That only works if flex is active. Not an e85 ONLY tune.

I do that on flex tunes.

Now I can take your flex tune and lock it where it never looks for 93 octane also.

2 different methods."

 

[engineermike]

He clearly didn’t understand what I meant. I tried.

 

[Biggness]

He clearly didn’t understand what I meant. I tried.

This is his response to that:

"I see what he means. He's meaning apply the Flex changes from the truck directly to the MBT tables. But I honestly don't see that working because it's Throttle that blips, not timing."

 

[engineermike]

I understand it’s the throttle that blips not the timing. What I’m saying is that changing mbt changes the torque calculation. If it thinks timing is well below mbt then it will open the throttle more to compensate and achieve desired torque, but now its making more torque than desired because the actual timing is closer to actual mbt.

One way I’ve seen this issue band-aided by others was zero’ing out the coastdown shift map. It’s not the correct solution but it could at least mask the problem.

If it were me, I would immediately put all the mbt tables back to stock and test it out. If I’m wrong; I’m wrong, but it’s a super easy test to at least rule out the most likely culprit and only takes like 15 minutes to try. It’s the only thing you listed that changed that could have this effect. If it works, then you can always just add to mbt at the higher loads and rpm.

If I do a dedicated e85 tune, I’m going offset all mbt tables by ford’s e85 offset and max out all the borderline tables. I believe that’s the most technically accurate way to do it short of doing a lot of dyno testing to verify ford’s mbt is accurate.

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