Fuel trims adapting after reflash. How long?

ManBearPig · Oct 12, 2017

I flashed back to my stock tune for a brief time and am now back to my Lund tune. I noticed I was getting some knock at part throttle and at throttle top in after a hard shift the first couple times I "got in it" after flashing the tune back in. The knock has slowly gotten less and less prominent over the last 100 miles but I still will get the odd positive knock number on the ngauge for a split second at part throttle. I've also noticed positive knock numbers occasionally when revving the car in neutral. I assume this is because my fuel trims haven't "learned" yet as nothing else has changed. I do recall going through this after the first time I tuned the car....a datalog after 30 miles showed fuel trims were off, then another one I did a month later looked great. I don't drive the car much so I don't remember how many miles passed in that month between logs but my last log got a thumbs up and in several thousand miles since I've never seen any knock. WOT I see only negative numbers and the car still pulls like a banshee. I just see a flash of red (I have the ngauge set to go red with positive knock) every so often. How long does it take for the car to fully adapt back to what it should be doing? I would've guessed it would have taken about 30 miles but at just over 100 since the reflash I'm still seeing some activity I haven't seen since last time I flashed the car. Just wondering at what point I should no longer write it off as still learning.

CEHollier · Oct 12, 2017

Did you reflash the stock tune back before loading the Lund Tune. If not I would do that. Even Lund advises this. Should be immediate. When changing fuels 93 vs 85 drive 15 minutes to adapt. Edit - I had a 93 tune on my car and got a flex tune. Didn't flash back to factory and went 93 to 85. Ran like crap. Beefcake suggested the stock trick and it worked well.

I <3 Boost · Oct 12, 2017

ManBearPig said:
I flashed back to my stock tune for a brief time and am now back to my Lund tune. I noticed I was getting some knock at part throttle and at throttle top in after a hard shift the first couple times I "got in it" after flashing the tune back in. The knock has slowly gotten less and less prominent over the last 100 miles but I still will get the odd positive knock number on the ngauge for a split second at part throttle. I've also noticed positive knock numbers occasionally when revving the car in neutral. I assume this is because my fuel trims haven't "learned" yet as nothing else has changed. I do recall going through this after the first time I tuned the car....a datalog after 30 miles showed fuel trims were off, then another one I did a month later looked great. I don't drive the car much so I don't remember how many miles passed in that month between logs but my last log got a thumbs up and in several thousand miles since I've never seen any knock. WOT I see only negative numbers and the car still pulls like a banshee. I just see a flash of red (I have the ngauge set to go red with positive knock) every so often. How long does it take for the car to fully adapt back to what it should be doing? I would've guessed it would have taken about 30 miles but at just over 100 since the reflash I'm still seeing some activity I haven't seen since last time I flashed the car. Just wondering at what point I should no longer write it off as still learning.

I’m glad someone posted this. I planned to message Lund about this issue but hadn’t got around to it yet. I’m really eager to hear some suggestions / feedback. I have actually noticed the same exact thing happening with my car after a flash. Regardless of the length of time driving, long after the tune has “learned” the fuel trims I still get knock under the same driving scenarios listed above (typically less than 2 degrees of knock).

After I refill with a fresh tank of e-85 the knock disappears completely.

I <3 Boost · Oct 12, 2017

CEHollier said:
Did you reflash the stock tune back before loading the Lund Tune. If not I would do that. Even Lund advises this. Should be immediate. When changing fuels 93 vs 85 drive 15 minutes to adapt. Edit - I had a 93 tune on my car and got a flex tune. Didn't flash back to factory and went 93 to 85. Ran like crap. Beefcake suggested the stock trick and it worked well.

I did not try this. Thanks for the suggestion! I will try this in the future.

ManBearPig · Oct 12, 2017

I'm not running a flex tune. This is 93 only.

CEHollier · Oct 12, 2017

ManBearPig said:
I'm not running a flex tune. This is 93 only.

Same applies. Reflash factory then Lund 93. It worked for me. If that doesn't work contact Lund.

I <3 Boost · Oct 12, 2017

CEHollier said:
Same applies. Reflash factory then Lund 93. It worked for me. If that doesn't work contact Lund.

Following the prompts on the Ngauge, do you start the car with the factory tune? Then, turn the car off and flash the desired tune?

CEHollier · Oct 12, 2017

I <3 Boost said:
Following the prompts on the Ngauge, do you start the car with the factory tune? Then, turn the car off and flash the desired tune?

No. Do not start. Just reflash.

ManBearPig · Oct 12, 2017

That's what started this....I flashed back to the stock tune to compare some driving characteristics. Drove on the stock tune maybe 10 miles. Flashed my Lund tune back. Now I'm seeing the odd positive knock value under part throttle. The first few miles it was pretty consistent. Now at 100 miles it's only here and there. I know long term fuel trims have to adapt after a reflash (or after disconnecting the battery, or any time KAMis cleared). Just wondering how long that should take.

CEHollier · Oct 12, 2017

ManBearPig said:
That's what started this....I flashed back to the stock tune to compare some driving characteristics. Drove on the stock tune maybe 10 miles. Flashed my Lund tune back. Now I'm seeing the odd positive knock value under part throttle. The first few miles it was pretty consistent. Now at 100 miles it's only here and there. I know long term fuel trims have to adapt after a reflash (or after disconnecting the battery, or any time KAMis cleared). Just wondering how long that should take.

My car was running poorly after a retune. Contacted Beefcake and that was his recommendation. I did it and it worked. Give it a try. What do you have to lose?

stevnoof1 · Oct 12, 2017

I don't have a lund tune but my car is tuned. I see the knock sensors go off probably 25% of the time in first or second gear under very light throttle. Usually just a split second sometimes a little longer +0.5 sometimes up to +2.0. No clue what causes it I try to ignore it. Have been told I have false knock issue with the car on wot pulls sometimes after gear shifts as well. Fuel doesn't change anything. Never had any knock on a single gear pull ever.

markmurfie · Oct 13, 2017

The answer to your question is the long term fuel trims are always adapting to the patterns and trends in the short term trims for closed loop and adaption corrections applied to open loop.

So if your tune is learning and correcting in accurate tables in the ecu you need to watch for when the LTFT stop increasing or decreasing in one direction and hover around a specific value.

The way the KAM works is it assigns different LB/min to memory cells in the ECU. It then determines error values for those cells that we log as LTFTs. The fuel for MAF values is then corrected based on what cells it falls into. There is interpolation involved when the ECU applies the error from the cells, but it gives you a few target MAF values to try to get steady state logs of to monitor the changes in LTFT.

Not useful to any one but a tuner:
The pictures are of a stock MAF curve and modified curve. If the curve is modified to the extent that one cell is much larger and another smaller than it should be, it could make the ECUs job of determining the LTFT error for that small cell much harder. The KAM v airmass table should be modified to allow the ECU an easier time determining the LTFTs by extending the range of MAF period each cells covers to at least the stock cell sizes.

Kahboom · Oct 13, 2017

Me personally I return to the stock tune before flashing the new tune and then after flashing the new tune I do the Kam reset and crank position sensor relearn just to knock it all out to rule anything out.

Burkey · Nov 2, 2017

Um....I swap between flex and race tune semi-frequently and have never flashed back to stock in between.
Am I doing it wrong?

Kahboom · Nov 2, 2017

Not necessarily doing it wrong it is just recommended by most tuners to flash back to stock before flashing another tune. Some people never do this and don't have any problems While others can have errors that occur and cause the car to run poorly.

Fuel trims adapting after reflash. How long?

ManBearPig

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CEHollier

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I <3 Boost

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I <3 Boost

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ManBearPig

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CEHollier

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I <3 Boost

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CEHollier

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ManBearPig

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CEHollier

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stevnoof1

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markmurfie

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Kahboom

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Burkey

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Kahboom

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