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Negative LTFT

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14 Jan 2020 20:33 #36625 by Tondt
Negative LTFT was created by Tondt
2002 Ford Escape 3.0 has -20 LTFT and 20 STFT at idle or coasting. More RPM LTFT and STFT go to much smaller numbers but again cancel out. Should I be worried that LTFT and STFT are so high or is it more important that total fuel trim is 0? No DTC, no misfires, no hesitation, no problems. Do I have an issue or zero fuel trim is the bottom line and I should move on?

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14 Jan 2020 23:33 #36629 by scannerjohn
Replied by scannerjohn on topic Negative LTFT
LTFT are a learned response to an engine condition. STFT are used to bring the LTFT back to stoich. Ford's usually set codes at 25.

What are the voltage readings for the upstream 02's.

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15 Jan 2020 17:03 #36655 by Tondt
Replied by Tondt on topic Negative LTFT
Right, but I can't get that information for about a week I am traveling.
Just trying to find out what is the most important factor.
Total fuel trim near zero or LTFT near zero?
What do you think is the better direction?
Appreciate your opinion

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  • Tutti57
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15 Jan 2020 20:46 #36660 by Tutti57
Replied by Tutti57 on topic Negative LTFT
Total at zero is perfect but STFT is always going to be fluctuating a little. Remember that long term is an adjustable base point set after short term has moved for long enough. LTFT 0/STFT 0. LTFT 0/STFT 10. LTFT 10/STFT0. LTFT 10/STFT 10 LTFT20/STFT0. Hopefully that exaggerated example of an increasing lean condition makes sense. Pretend that is an air leak getting worse over the course of a few days, checked at idle.

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16 Jan 2020 08:40 #36662 by juergen.scholl
Replied by juergen.scholl on topic Negative LTFT
Clear the KAM and watch what happens....

An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.

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16 Jan 2020 10:47 #36665 by scannerjohn
Replied by scannerjohn on topic Negative LTFT
my opinion is that LTFT at 0 is what you want.

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