Fuel Trim question
04-10-2003, 06:36 PM
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Fuel Trim question My LTFT on each bank is off by quite a bit:
LTFT1 at Cell 6 to 15: 19.97
LTFT2 at Cell 6 to 15: 9.80
LTFT1 at Cell 22: 12.87
LTFT2 at Cell 22: 3.66
LTFT1 at for all Cells: 17.07
LTFT2 at for all Cells: 7.16
So I was guessing that I have an intake leak. But my STFT was pretty even:
STFT1 at Cell 6 to 15: -0.80
STFT2 at Cell 6 to 15: -0.76
STFT1 at Cell 22: -1.03
STFT2 at Cell 22: -1.12
STFT1 at for all Cells: -0.68
STFT2 at for all Cells: -0.83
If one of my LTFT is way off, should be the STFT be off too?
Here is my Average Injector Pulse Width:
Bank 1: 6.17 ms
Bank 2: 5.36 ms
O2 sensor average:
B1S1: 413.79 mv
B2S1: 408.61 mv
One of my #7 plug was dead last week so the car was driven in 7 cylinders while I tried to diagnose the problem. So I know that bank 1 LTFT was at 25% last week. Could it be that LTFT has yet to learn of the fix?
Also, I am having a lot of back fires (popping noise at exhaust), could this be related?
LTFT1 at Cell 6 to 15: 19.97
LTFT2 at Cell 6 to 15: 9.80
LTFT1 at Cell 22: 12.87
LTFT2 at Cell 22: 3.66
LTFT1 at for all Cells: 17.07
LTFT2 at for all Cells: 7.16
So I was guessing that I have an intake leak. But my STFT was pretty even:
STFT1 at Cell 6 to 15: -0.80
STFT2 at Cell 6 to 15: -0.76
STFT1 at Cell 22: -1.03
STFT2 at Cell 22: -1.12
STFT1 at for all Cells: -0.68
STFT2 at for all Cells: -0.83
If one of my LTFT is way off, should be the STFT be off too?
Here is my Average Injector Pulse Width:
Bank 1: 6.17 ms
Bank 2: 5.36 ms
O2 sensor average:
B1S1: 413.79 mv
B2S1: 408.61 mv
One of my #7 plug was dead last week so the car was driven in 7 cylinders while I tried to diagnose the problem. So I know that bank 1 LTFT was at 25% last week. Could it be that LTFT has yet to learn of the fix?
Also, I am having a lot of back fires (popping noise at exhaust), could this be related?
04-10-2003, 09:09 PM
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Staging Lane
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Re: Fuel Trim question It is not true that if the LTFTs are much different that the STFT would be different also. This is so because when the STFT value hits a certain limit, the PCM adjusts the LTFT value toward that same direction and sets the STFT back to 0% and the process starts all over again.
Since fixing the #7 plug problem, how much has the car been driven? You will have to visit each fuel cell for at least a few minutes each for PCM relearn.
Could you have a bad O2 sensor? Or maybe a vacuum leak?
My LTFTs from bank 1 to bank 2 differ by about 2 to 3%. That would be attributed to the difference in O2 sensors from side to side.
BTW: Dont even bother to log the STFT values. There is nothing to be gotten here.
Since fixing the #7 plug problem, how much has the car been driven? You will have to visit each fuel cell for at least a few minutes each for PCM relearn.
Could you have a bad O2 sensor? Or maybe a vacuum leak?
My LTFTs from bank 1 to bank 2 differ by about 2 to 3%. That would be attributed to the difference in O2 sensors from side to side.
BTW: Dont even bother to log the STFT values. There is nothing to be gotten here.
04-10-2003, 09:13 PM
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Staging Lane
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Re: Fuel Trim question Another idea, after checking for a vacuum leak and not finding one, switch the O2 sensors from side to side (the front ones) and allow the PCM to relearn. If the LTFTs flip, then you will know that one of the sensors are bad,, if one is bad, it is most likely the one in bank 1 (just a guess).
04-10-2003, 10:22 PM
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Re: Fuel Trim question Any intake tract or vacuum leak will be
decreasingly significant as you increase
airflow. It will be a vanishing percentage
at WOT and even part throttle, unless the
cross-sectional area of the leak is on the
order of the throttle opening (not likely).
If you have a relatively consistent mixture
error then that points more to measurement
of airflow, fuel pressure, etc; something that
will be an air or fuel scale factor, rather than
an offset (leaks being a fixed orifice airflow
offset, depending almost solely on MAP).
decreasingly significant as you increase
airflow. It will be a vanishing percentage
at WOT and even part throttle, unless the
cross-sectional area of the leak is on the
order of the throttle opening (not likely).
If you have a relatively consistent mixture
error then that points more to measurement
of airflow, fuel pressure, etc; something that
will be an air or fuel scale factor, rather than
an offset (leaks being a fixed orifice airflow
offset, depending almost solely on MAP).
