LTFT Tuning Question?
06-15-2008, 09:34 PM
#1
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LTFT Tuning Question? Im about to do LTFT tuning and was reading a sticky on here thats about 25 pages long about how to tune. What im confused about is when tuning LTFT's it says to:
Richen this cell by increasing the VE table value by the amount of the LTFT value. The operation is opposite for negative LTFT's.
If LTFT = (4), VE cell value is 67, result would be (67)+(4)=71 - increasing the VE, which is adding fuel. If the LTFT was (-4), the result would be (67)+(-4)=63, decreasing VE and thus reducing fuel. To decrease LTFT values, a smaller number or number closer to zero, ADD the difference between the positive LTFT value and zero to the corresponding cell in the VCM Editor>Edit>Engine>Airflow>Main VE>Primary VE vs. RPM vs. MAP table. To increase a LTFT value, a larger number or number farther away from zero, SUBTRACT the difference between the LTFT value and zero and SUBTRACT from the corresponding cell in the VCM Editor>Edit>Engine>Airflow>Main VE>Primary VE vs. RPM vs. MAP table. For example, In the VCM Scanner>Histogram display, the (.8, 40) cell, 800 RPM's and 40 kPa, is 4. To bring the VCM Scanner>Histogram display>LTFT cell (.8, 4.0) DOWN to 0 from 4 ADD 4 to the (.8, 4.0) cell in the VCM Editor>Edit>Engine>Airflow>Main VE>Primary VE vs. RPM vs. MAP table. If the VCM Scanner>Histogram display>LTFT cell (2.0, 30) is -10, SUBTRACT 10 from the (2000, 30) cell in the VCM Editor>Edit>Engine>Airflow>Main VE>Primary VE vs. RPM vs. MAP table to bring it UP to 0. This will not work out exactly but will be VERY CLOSE.
SO basically are you altering the VE twice? Like in the first part is says to add or subtract the LTFT from the scanner into the editor, then in the second part its talking about getting it to 0. Am i just stupid and the second part of the examples is just going about explaining it more in depth? SO lets say i reset my ltfts and go for a good cruise to hit as many cells as possible and then tune my VE, do i have to go for another drive and try to hit as many cells as possible again? DO i have to adjust anything in the secondary VE? thanks guys
Richen this cell by increasing the VE table value by the amount of the LTFT value. The operation is opposite for negative LTFT's.
If LTFT = (4), VE cell value is 67, result would be (67)+(4)=71 - increasing the VE, which is adding fuel. If the LTFT was (-4), the result would be (67)+(-4)=63, decreasing VE and thus reducing fuel. To decrease LTFT values, a smaller number or number closer to zero, ADD the difference between the positive LTFT value and zero to the corresponding cell in the VCM Editor>Edit>Engine>Airflow>Main VE>Primary VE vs. RPM vs. MAP table. To increase a LTFT value, a larger number or number farther away from zero, SUBTRACT the difference between the LTFT value and zero and SUBTRACT from the corresponding cell in the VCM Editor>Edit>Engine>Airflow>Main VE>Primary VE vs. RPM vs. MAP table. For example, In the VCM Scanner>Histogram display, the (.8, 40) cell, 800 RPM's and 40 kPa, is 4. To bring the VCM Scanner>Histogram display>LTFT cell (.8, 4.0) DOWN to 0 from 4 ADD 4 to the (.8, 4.0) cell in the VCM Editor>Edit>Engine>Airflow>Main VE>Primary VE vs. RPM vs. MAP table. If the VCM Scanner>Histogram display>LTFT cell (2.0, 30) is -10, SUBTRACT 10 from the (2000, 30) cell in the VCM Editor>Edit>Engine>Airflow>Main VE>Primary VE vs. RPM vs. MAP table to bring it UP to 0. This will not work out exactly but will be VERY CLOSE.
SO basically are you altering the VE twice? Like in the first part is says to add or subtract the LTFT from the scanner into the editor, then in the second part its talking about getting it to 0. Am i just stupid and the second part of the examples is just going about explaining it more in depth? SO lets say i reset my ltfts and go for a good cruise to hit as many cells as possible and then tune my VE, do i have to go for another drive and try to hit as many cells as possible again? DO i have to adjust anything in the secondary VE? thanks guys
06-15-2008, 11:03 PM
#2
I would suppose a second pass would help or at least tell you if the changes made a difference. You have to realise the LTFT cells are not of the same resolution as the VE so basically you are filling in large blocks of the VE at a time.
Because you are filling in large blocks at one time you don't have to hit all of the VE cells. Say 1200 RPM to 2000 RPM and 30 KPA to 50 KPA will all be the same so just get some measurements for that LFTF cell and then apply them to all VE cells in that region. I made up that cell though. You will have to determine how your PCM set them up.
It is better than nothing. Better than just tweaking your fuel pressure like we used to do in times of old.
Because you are filling in large blocks at one time you don't have to hit all of the VE cells. Say 1200 RPM to 2000 RPM and 30 KPA to 50 KPA will all be the same so just get some measurements for that LFTF cell and then apply them to all VE cells in that region. I made up that cell though. You will have to determine how your PCM set them up.
It is better than nothing. Better than just tweaking your fuel pressure like we used to do in times of old.
