LTFT goes really negative when first adding e85 in car

bybcous · 04-26-2017, 06:28 PM

For thr first 6 -7 minutes or so it will read - 41 to -40. Does this sound right? Its like its taking a while for car to realize e85 was added to my 93. After 5-6 minutes it will make its way back to 0. My e85 reading was still at 30% and as the thr e85% on my gauge went up, the ltft evens back out to 0.

cmitchell17 · 04-26-2017, 09:45 PM

Ive noticed this exact same thing. LTFTs will go -30 to -40, which they should be positive as alcohol composition increases, as long as stoic is still commanded at 14 to 1.

My guess is that's the composition sensor is detecting the increased alcohol content and commanding stoich down from 14:1, but maybe theres still a mix of 14 to 1 gas in there and its just temporarily running rich and the 02 sensors are seeing this and trying to compensate.

Maybe there are tables in HP tuners we don't have access to that control transient conditions that are zeroed out in the non-flex fuel calibrations so we are seeing the fuel trims freaking out until we get a steady state fuel composition.

bybcous · 04-27-2017, 08:59 AM

Quote:

Originally Posted by cmitchell17

Ive noticed this exact same thing. LTFTs will go -30 to -40, which they should be positive as alcohol composition increases, as long as stoic is still commanded at 14 to 1.

My guess is that's the composition sensor is detecting the increased alcohol content and commanding stoich down from 14:1, but maybe theres still a mix of 14 to 1 gas in there and its just temporarily running rich and the 02 sensors are seeing this and trying to compensate.

Maybe there are tables in HP tuners we don't have access to that control transient conditions that are zeroed out in the non-flex fuel calibrations so we are seeing the fuel trims freaking out until we get a steady state fuel composition.

Yea, it is taking a while for the computer to realize we just put e85 in car, ima just take it easy for now on until computer catches up

04-26-2017, 06:28 PM	#1
bybcous Drives: 2016 Hyper Blue 1SS Join Date: Jul 2015 Location: hampton roads Posts: 2,763	LTFT goes really negative when first adding e85 in car For thr first 6 -7 minutes or so it will read - 41 to -40. Does this sound right? Its like its taking a while for car to realize e85 was added to my 93. After 5-6 minutes it will make its way back to 0. My e85 reading was still at 30% and as the thr e85% on my gauge went up, the ltft evens back out to 0. __________________ 1ss/Auto-Hyper Blue acs carbon flash spoiler, bmr springs, gm clear tails. Texas speed cam, 223/227 .635/.635 116 LSA, Kooks Long Tube Headers with green cats, MSD Atomic Air Force Intake, CAI Cold Air Intake, QTP cutouts. 503 hp Best so far 11.5 at 123 with a 1.83 60ft. BMR lower and upper trailing arms and upper control arms,E85 DELIVERED 12/29/15 http://youtube.com/bybcous " no talking only racing on my youtube"

04-26-2017, 09:45 PM	#2
cmitchell17 Drives: 17 2SS, 8L90, Cam, Heads, E85 Join Date: Dec 2016 Location: US Posts: 1,201	Ive noticed this exact same thing. LTFTs will go -30 to -40, which they should be positive as alcohol composition increases, as long as stoic is still commanded at 14 to 1. My guess is that's the composition sensor is detecting the increased alcohol content and commanding stoich down from 14:1, but maybe theres still a mix of 14 to 1 gas in there and its just temporarily running rich and the 02 sensors are seeing this and trying to compensate. Maybe there are tables in HP tuners we don't have access to that control transient conditions that are zeroed out in the non-flex fuel calibrations so we are seeing the fuel trims freaking out until we get a steady state fuel composition.

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