help me understand LTFT/STFT

[blcknspo0ln]

taken from the tech article:
2g: 2g's only have 2 fuel trims, a long term fuel trim (LTFT) and a short term fuel trim (STFT). The STFT varies with the O2 sensor, an the LTFT goes for every rpm range. Since the STFT directly effects the LTFT, then you can just add the two together, and tune from there. For example, if the LTFT is +20%, and the STFT is -5%, you are at approximately +15%.

You can also do this addition trick on a 1g with a TMO/Pocketlogger type setup.

Whew, that was exciting, but I think I covered it all. Now, on to the tuning. Set up your logger to display RPM, Airflow, and all the fuel trims your car has. Start the car and let it fully warm up. Leave it at idle, and we will begin to tune the low throttle table in the SAFC.

Now, look at the low fuel trim (2g's only have the LTFT). If it is positive, add a few percent on the SAFC at the 1000 rpm point. This is not an exact science, but usually for about every 3-5% on the logger, you need 1% on the SAFC. After adding or subtracting a few percent, let the car idle for a few minutes, and watch the fuel trims change. This may take a while, especially in a 1g, so just wait.

i forget the exact numbers so basically.. what am i looking for? am i trying to tune the STFT to 0 or the LTFT to 0? or do i just want both the STFT and LTFT to have a 0 difference [ both equal to each other ]?

i'm basically just beginning to log and have no idea what's going on. reading the tech articles just confuse me even more. any pointers from you tunerstein/safc2 loggers?

[just monitoring no log yet, still gotta figure out how to use this thing ] on a 3rd gear pull i'm getting at 4k .97volts on bank 1 and 1-5 degrees of timing. i know somethings messed up and i'm running rich, but when i tried richening and leaning 3% either way, it would bring my timing down to 0

wtf is going on!?

 

[98spydert]

Running really rich tends to screw up the timing curve pretty bad and make it seem like you're getting bad knock.

The STFT is basically what the O2 sensor is telling the ECU. For example you're running a little rich and the O2 sees that, it tell the ECU it's about 5% rich and the ECU takes 5% fuel away. You can see this through your STFT when it says -5.
When you're comsistantly 5% rich at a given airflow range (you're STFT will read -5 for consistantly at the same throttle/rpm), the ECU will remember this and always apply that adjust ment. That long term adjustment is now -5 and your LTFT shows this. Now that the 5% is being taken away using the long term memory, the O2 sensor see's the a/f is ok and reads 0.

Now you've got a STFT and a LTFT for three ranges based on airflow seen by the MAFT idle range, mid range, and WOT.. Unfortunatly you've only got one display for STFT. So when you're at idle the STFT or LTFT display on your logger is displaying the idle range, but when you accelerate it changes to the mid range then WOT range but the display always says STFT and LTFT respectivly. The values change but it doesn't look like it to the untrained eye

hope this helps you understand a little better, I'm not good at explaining it

 

[1LE]

The ECU gradually adjusts the LTFT in order to make STFT be 0 in each rpm range. If your LTFT hovers around 0, you're doing real good.

 

[blcknspo0ln]

awesome thanks for the info guys, i'm starting to get this whole tuning deal.

LTFT is right around 0 now at a +15 @ 1k rpm lo setting