How do long term fuel trims work?

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Nov 1, 2012 | 11:11 AM

gpr

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How do long term fuel trims work?

Was doing some scanning this morning and noticed that one bank is consistently 4% higher than the other bank when cruising down the road. What I'm wondering is how exactly long term fuel trims work and where are they stored?

When I first got the car one of the cats was plugged and i didn't know it for a while so the trims were always way out of whack. I'd thought by now they would have settled down. I don't have any header leaks so I'd assume both sensors should read the same. Is there a way i can go clear out all long term fuel trims? This way they aren't influencing the tune and i can start fresh to see if there is an issue or it is the stored ltft that are affecting it.

Nov 1, 2012 | 11:32 AM

redtan

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Unplug the battery for a few minutes...that resets the trims.

Nov 1, 2012 | 10:24 PM

lsx1

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If you have hpt, you can clear them out in the scanner under vcm controls.

Nov 1, 2012 | 10:28 PM

im-not-guilty

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From: Maine

I'm not to sure about the hi-perf stuff .
But being only 4% LTFT on a stock gm is nothing to worry about

Nov 2, 2012 | 05:52 AM

06X6spdGTO

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From: Kearney, NE

Any + LTFT will be added to the PE equation in percent ratio... So a + LTFT of 5% would add 5% more fuel to the 12.50 Commanded AFR when the car is put in to PE.....

LTFT are a combined average of the STFT's.... The LTFT attempts to settle your STFT's closer to zero... BUT STFT will NOT add fuel to the PE equation...

Hope this helps...

To clear them simply unhook the battery for a few mins...

Nov 2, 2012 | 01:39 PM

gpr

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I am using efilive, so I guess i will have to un hook battery for a bit. I don't mind having small percentages for the ltft, what bothers me is when the left and right bank vary by 5%. something seems wrong at that point.

Thanks for the help!