how much will the ecu try to adjust the fuel while in closed loop

[turboengnr]

no problem. I am just happy i remembered that. I havent driven (let alone tuned) my civic since febuary.

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[liljoe]

so, couldn't you just disconnect your battery all the time so it doesn't "learn" anything differnt than what you tune it too?
i.e you disconnect you battery and then tune you car. and then everytime you take it out you disconnect your battery again. that way your always starting at the same point?
if so, is there an easier way to reset the learned fuel trims? maybe an OBDII scantool?

[turboengnr]

no, because when you disconnect the battery, it automatically starts learning everything. It then programs the long term fuel trims and updates is constantly. It can change the long term every second or more within the first few minutes of driving.

[BlackFire]

Then, I don't see how any piggy back could help on a daily driven car if it will do what it wants to, even using a +40% setting if it locked a -15% it will make you run lean at WOT.
Then why spend money on piggy backs???
Please right me, I know I have to be wrong but I can't see how those piggy backs could help then or how to do the tuning in a way that the ECU won't bother?

[turboengnr]

because you can still tune at WOT. You just need to have the proper tuning during the non-WOT part of the map.

once you get the fuel trims dialed in, you will have an extremely consistent a/f curve.

[Havok2k1]

Good explanation.

Added to TFAQ

[gearbox]

so is there a right or wrong way to relearn on an NA car after resetting the ecu? Do you need to drive a certain way? And when tuning using a vafc, I guess you can only do wot settings?

[tfnaaf]

Ijust watched short term and long term on my car. Short term changes a lot and the long term didnt seem to change much so that would mean its in good tune?

[leonhsieh]

Originally Posted by turboengnr

no prob

it is actually quite simple.

you need some sort of OBDII scanner that has a data streaming capability.

When you have that, set it up to watch the LT_Ftrm and the ST_Ftrm (long and short term fuel trims). When you have that, you need to have your laptop setup to watch your fuel tables in real time.

When you have those set up, you need to start cruising at low RPM (around 2k) and then start accellerating with a specific amount of throttle. You then watch both the fuel trims on the scanner and the fuel map on the laptop. When you see the fuel trims start to add or subtract fuel, you do the same on the fuel map.

so lets say you are at 3250 RPM and the scanner shows a LT_Ftrm of -2% and a ST_Ftrm of -14%. You should gradually take out fuel in the fuel map until the fuel trims come back down to around zero.

The difference between the LT_Ftrm and the ST_Ftrm is simple. The ST_Ftrm's are what the computer is doing at that specific point in time. The LT_Ftrm is the trend that the computer is seeing.

You know how they say your computer "learns"? Well, they are talking about the LT_Ftrm. Over time, the computer averages out the data it recieves and outputs it as a single variable (LT_Ftrm). When this is at or close to 0%, that means that you spend most the time with a 0% fuel trim correction factor.

When you disconnect the battery, this is the value that gets erased and must be "re-learned" in order for the car to run at its potential.

Typically i like to see fuel trims between +5% and -5% on the LT_Ftrm.

I am confused. Correct if i am wrong. From what i read, STFT will alwasy hunt for desired a/f ratio under closed loop. So, if u try to make STFT to 0% with obd2 scanner, i think you are running close to desired a/f ratio(14.7). Isn't that too lean under boost? Also,I don't think LTFT will change immediately. LTFT will change if STFT keep making correction over time and it will transfer that setting to LTFT. And if LTFT changed, your tuning for WOT will mess up. That's why i reset my ecu every 3 days to not let STFT touch my LTFT. Again, correct me if i am wrong.

[turboengnr]

what was the long term like? Was it between -5% and +5%?


to make it relearn correctly, drive the car like you normally do.

[tfnaaf]

Originally Posted by turboengnr

what was the long term like? Was it between -5% and +5%?


to make it relearn correctly, drive the car like you normally do.

It was between those values. But i only did this under light load. As i know im VERY rich under heavy load. I still need to pull a LOT of fuel out under WOT

[turboengnr]

leon, you are partially correct.

But one aspect that you need to look at is what a/f ratio the car is looking for under load. I know when i was at ~75% throttle with my car NA, the car ran in the mid 12's a/f. The car knows when it needs to be lean and when it needs to be rich.


The problem with resetting it every few days is this....

when you let it learn everything, it takes a while for anything to change the LT_Ftrm's,. When you reset the ecu, it updates it constantly.


but as long as your ST_Ftrm is constantly out of a desired range, then you need to tune to bring those within the limits.

[leonhsieh]

Ok..thx for the info

[kezay]

very informative thread.

[supermex]

So how the Split Second ES1 play a part in all these?