Correlating Evoscan Fuel Trim to OBD-II LTFT
#1
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Correlating Evoscan Fuel Trim to OBD-II LTFT
Did some logging last night, trying to see where my fuel trims are at after the injector rescaling efforts of the past week.
Here's what I've got so far, on back-to-back OBD-II and Evoscan sessions, I recorded the following values:
Dynoscan (OBD-II) ... Evoscan (MUT-III)
-----------------------------------------------------
5.50% LTFT ... 124.2188 FuelTrim_Middle
2.30% LTFT ... 110.9375 FuelTrim_Middle
4.70% LTFT ... 117.1875 FuelTrim_Middle
That leaves me with a formula of:
LTFT = ( FuelTrim_Middle - 100 ) / (x)
where x is between 3.6 and 4.7.
I will do more logging when I drive the car around some more. If anyone can log some more OBD-II and Evoscan numbers, maybe we can come up with a constant for (x) ...
l8r)
Here's what I've got so far, on back-to-back OBD-II and Evoscan sessions, I recorded the following values:
Dynoscan (OBD-II) ... Evoscan (MUT-III)
-----------------------------------------------------
5.50% LTFT ... 124.2188 FuelTrim_Middle
2.30% LTFT ... 110.9375 FuelTrim_Middle
4.70% LTFT ... 117.1875 FuelTrim_Middle
That leaves me with a formula of:
LTFT = ( FuelTrim_Middle - 100 ) / (x)
where x is between 3.6 and 4.7.
I will do more logging when I drive the car around some more. If anyone can log some more OBD-II and Evoscan numbers, maybe we can come up with a constant for (x) ...
l8r)
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To be honest, my idle is so erratic that I'm having a very hard time tracking any kind of trends. Usually it hovers just below 14.7, but then it'll jump to 16.8 and immediately nosedive to 12 or less or vice-versa. It seems like it's a little on the lean side, since LTFTs slowly go up at idle. Once I'm confident in/happy with the overall injector scaling, I will start playing with the injector latency settings at 14V.
l8r)
l8r)
#5
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Originally Posted by AMS
Have you noticed that idle fueling is not affected by fuel map values?
The good news is, if you can get those fuel trims real close to zero, the car will cold start perfectly.. But otherwise you'd have to disconnect the O2 sensor to keep it from going into closed loop to alter that portion of the fuel table.
But I thought I was the only one.. Not only that, my fuel trims never seem to change, at least all that frequently.. And I really doubt my closed loop adjustments are so close to perfect that they don't need any trimming at the moment..
Anyone think maybe those fuel trim values aren't updated very frequently.. One of mine is always at 100%, another is around 50%, and the third is always at 113.. Never seems to change though...
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Originally Posted by MalibuJack
Anyone think maybe those fuel trim values aren't updated very frequently.. One of mine is always at 100%, another is around 50%, and the third is always at 113.. Never seems to change though...
Just look at your STFT....that will tell you if your LTFT needs adjusting. It may just not have time to do it, depending on how you are driving.
Eric
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Originally Posted by MalibuJack
Anyone think maybe those fuel trim values aren't updated very frequently.. One of mine is always at 100%, another is around 50%, and the third is always at 113.. Never seems to change though...
l8r)
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Originally Posted by MalibuJack
I guess its possible that my trims are close enough that they may not update frequently, I just didn't think that was actually possible.
#10
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See, thats kinda what I see, at least one of those trims stays at 100 all the time, the others are somewhere over 50 and the other is 115 or so.. And rarely change..
I guess my point was it doesnt clearly show STFT and LTFT's like a regular OBD-II scanner so I'm having some difficulty getting my head around it.. At least if it never appears to change when I'm trying to make change..
I guess my point was it doesnt clearly show STFT and LTFT's like a regular OBD-II scanner so I'm having some difficulty getting my head around it.. At least if it never appears to change when I'm trying to make change..
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More log info:
Dynoscan (OBD-II) ... Evoscan (MUT-III)
-----------------------------------------------------
12.50% LTFT ... 150.00 FuelTrim_Middle
12.50% LTFT ... 150.00 FuelTrim_Middle
9.40% LTFT ... 139 FuelTrim_Middle
9.40% LTFT ... 139 FuelTrim_Middle
9.40% LTFT ... 137.5 FuelTrim_Middle
9.40% LTFT ... 137.5 FuelTrim_Middle
Looks like the multiplier hovers around 4. This set of data was taken by me switching between Evoscan and Dynoscan as fast as I could (maybe 30 seconds to switch) over approximately an hour's worth of putzing around town, running errands.
So for now I will assume the equation to be:
LTFT = ( FuelTrim_Middle - 100 ) / 4
Overall the FuelTrim_Middle stayed very consistent with the LTFT readings I was getting.
l8r)
Dynoscan (OBD-II) ... Evoscan (MUT-III)
-----------------------------------------------------
12.50% LTFT ... 150.00 FuelTrim_Middle
12.50% LTFT ... 150.00 FuelTrim_Middle
9.40% LTFT ... 139 FuelTrim_Middle
9.40% LTFT ... 139 FuelTrim_Middle
9.40% LTFT ... 137.5 FuelTrim_Middle
9.40% LTFT ... 137.5 FuelTrim_Middle
Looks like the multiplier hovers around 4. This set of data was taken by me switching between Evoscan and Dynoscan as fast as I could (maybe 30 seconds to switch) over approximately an hour's worth of putzing around town, running errands.
So for now I will assume the equation to be:
LTFT = ( FuelTrim_Middle - 100 ) / 4
Overall the FuelTrim_Middle stayed very consistent with the LTFT readings I was getting.
l8r)
#12
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i just installed one of al's base maps and my LTFT idleing is around -5, cruising around -11(on an OBD2 logger). does this sound far off from what i should be seeing? i asked al about it but didn't get an answer yet. are - leaning out or richening?
Last edited by hondafan; Jul 28, 2006 at 08:03 PM.
#13
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Originally Posted by hondafan
i just installed one of al's base maps and my LTFT idleing is around -5, cruising around -11(on an OBD2 logger). does this sound far off from what i should be seeing? i asked al about it but didn't get an answer yet. are - leaning out or richening?
Eric
#14
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Anything around 10% or less (plus or minus) is a good target and will generally run correctly.. The closer you can get to zero the better, but the base map is doing a very good job with it being that close..
Since there is a discrepency of -5 and -11, you can increase the injector latency slightly, it should get you real close (a small amount at a time) In one of the other posts it explains how latency can affect the cruise and idle and its trims.. It turns out that after monitoring the data, that the accel enrichment value may actually be a contributor also.
When I was logging data, what I noticed was the Accel enrichment would tend to tip-in on acceleration, but hover afterwards.. Let me know if you guys also see that.. since that can explain a few things I had seen..
Since there is a discrepency of -5 and -11, you can increase the injector latency slightly, it should get you real close (a small amount at a time) In one of the other posts it explains how latency can affect the cruise and idle and its trims.. It turns out that after monitoring the data, that the accel enrichment value may actually be a contributor also.
When I was logging data, what I noticed was the Accel enrichment would tend to tip-in on acceleration, but hover afterwards.. Let me know if you guys also see that.. since that can explain a few things I had seen..