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Author Topic: long term fuel trim  (Read 1591 times)

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birdman

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long term fuel trim
« on: 30 December 2011, 17:52:34 »
Hi there,does anyone know how the long term fuel trim is reset? I had an issue with fuel trim code P0170 for months and was eventually traced to a lazy maf sensor,although working was telling fibs! This was replaced with a gen vaux item.The long term trim was always at 10.2% but since the problem has been solved the fuel trim is still at 10.2%? Any ideas?No MIL light anymore though!!
Any answers greatly received! :y
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TheBoy

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Re: long term fuel trim
« Reply #1 on: 30 December 2011, 18:06:15 »
A code reader capable of resetting trims is required. Personally, I would only entrust this to a Tech2, seeing as the illegal readers that are all the rage seem more than capable of making matters worse.
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birdman

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Re: long term fuel trim
« Reply #2 on: 30 December 2011, 18:08:58 »
It was reset by Kevin Woods Tech2 but still shows 10.2% long term fuel trim? ::)
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TheBoy

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Re: long term fuel trim
« Reply #3 on: 30 December 2011, 18:11:59 »
Quote from: birdman on 30 December 2011, 18:08:58
It was reset by Kevin Woods Tech2 but still shows 10.2% long term fuel trim? ::)
Did it go to 0% when reset, or stay at 10%?  Also, how are you reading it, as it only displays in whole increments  :-\
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birdman

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Re: long term fuel trim
« Reply #4 on: 30 December 2011, 22:48:39 »
no it didnt go to zero,it reads 10.1%
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TheBoy

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Re: long term fuel trim
« Reply #5 on: 31 December 2011, 10:29:04 »
Quote from: birdman on 30 December 2011, 22:48:39
no it didnt go to zero,it reads 10.1%
What are you using to read them?
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birdman

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Re: long term fuel trim
« Reply #6 on: 31 December 2011, 10:55:51 »
my Autel Maxiscan MS509
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Kevin Wood

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Re: long term fuel trim
« Reply #7 on: 31 December 2011, 16:11:04 »
Sorry, Just spotted your PM. :-[

10% does sound a little on the high side. Are both banks reading the same or is it just high on one bank?

I wouldn't expect them to need resetting. They will correct themselves after a bit of driving following a MAF sensor change.

Clearing the codes usually resets the fuel trims on this ECU so I would try clearing the codes with your code reader and see if they drop to zero. If not, it might be that the code reader is not interpreting the data correctly.

If it's no longer raising fault codes the fuel trim obviously is no longer getting excessive, but I would normally expect it to be within a few percent of zero.
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TheBoy

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Re: long term fuel trim
« Reply #8 on: 31 December 2011, 17:43:07 »
Quote from: birdman on 31 December 2011, 10:55:51
my Autel Maxiscan MS509
Hmmm, wondering if its being a liar, as I've only ever seen it in whole increments, ie, no decimal places.

On petrol, long term trims will tend to fall back to 0% fairly quickly if the car is running right.
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birdman

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Re: long term fuel trim
« Reply #9 on: 31 December 2011, 19:25:46 »
guess ive still got more trouble to come!Engine runs like a gem,I will monitor,thanks for your help,happy new year! :)
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