E85 LTFT Above 10% at Idle
 

Hello, another fuel trim thread here.

I read all that I could understand about expected fuel trims for running on e85, but it seems like my LTFT hovers anywhere from +7% to +15%, averaged at 12%, never any lower than 7 at idle. Stock intake, just header and catback. Checked for exhaust leaks and none that I saw. It drops upon load and gets to ~5% @ 3k rpm so I assume that part is good. This happens across multiple fill ups, and fluctuates within the same tank/different days.

I've read that temperature can skew readings a bit and idle isn't crucial, but also that it should be within +/- 10% throughout. So why would this be and is it something to look into? Does this indicate a leak or would that be more severe values? Any suggestions? Thanks.

https://datazap.me/u/pizzachicken/9-...og=0&data=1-11
https://datazap.me/u/pizzachicken/9-...og=0&data=1-11

If this is a flex fuel tune and your running a flex fuel sensor then your fuel trim can be up to around 10% ltft on one fuel and zeroed on another fuel. This is usually normal.

O this is the base map OFT, no flex kit.

oft tunes have lowest fuel trims arround 70-75% ethanol if you hapoen to have true 85% ethanol then you will get high positive fuel trims

Hi Steve. A majority of my understanding of e85 is from your work on this forum actually so thank you.

Perhaps I'm interpreting your instructions wrong, but shouldn't "normal" ltft values stay within +/- 10%? Suppose it's possible I'm getting true 85% but these higher trims seem to be consistent throughout multiple fill ups and different stations rated for e70% - e85% (Los Angeles). So you're saying seeing up to 15% ltft at idle should not be alarming? If so i'll take your word. Would there be a max ltft % to allow before being concerned, and if so what else should I look into then?

if you have stock intake and no leaks intake or exhaust +15 is a little unusual. The leaks wont be huge and often hard to detect. From the logs it does look like a leak as trims are only high at idle then ok once rpm rises and you on throttle

Would high positive trims most likely be exhaust leak then or can it be intake as well? Believe I've seen you say intake leaks result in negative trims. I couldn't find any leaks at the flanges, unless it's a crack within the wrapped header piping or the shielding of the overpipe.. thought that was unlikely. Any other reason if I absolutely can't find a leak? And anyhow, is it safe to drive for the time being if it's just at idle? Thanks.

yes it would be safe to drive if its only big trim at idle


exhaist and ibtake leaks can send ltft high positive at idle it only takes a small leak

Hmm not really figuring this one out thus far, cannot find leaks. I've been monitoring more on the same tank this week. My trims are at 7% and stays around here instead of seeing a wide variance on/off throttle, at first. But after some driving, say 15 mins, I can watch ltft creep to 12.5% at idle and stay there, and then we can see the wide variance. Turn off car and let cool down for a bit, it's back to 7. Seems like temps has a role?

Also, if I happen to figure out a fix, can I expect to see it reflected in the trims immediately or would I have to get some miles in?

I also just switched to E85 with the 4.0x tune and am experiencing the same thing. No exhaust leaks. I haven't been able to monitor the WOT LTFT but next time I am at the track I will try to remember. Seems to be performing great. Solid boost over 93. Only other thing I have noticed since making the switch is that it takes the car a little longer to start. Otherwise I am pretty happy.