question about stft and ltft

[phunny]

when tuning these with the safc do you want them to equal zero when added together(ie stft -5 / ltft 5) or just get the stft to zero?

 

[CanadianTSi]

I focus on getting the STFT to 0 and don't really worry much about the LTFT although I think mine sits at -4...

 

[karbon]

I think the OP means as far as what to change it to to zero out the fuel trims. Yes, if your LTFT is say, 13%, then you must change the fuel mixture at that RPM range such that the STFT reads -13% consistently. Over time the ECU sees that the LTFT greatly exceeds the STFT and will move it down by a bit, and then the STFT will follow to maintain a stoich. mixture. You can watch this happen in the span of a couple minutes on a logger when you're idling (idle LTFT changes rapidly). Changing the LTFT at cruise RPMs takes much longer but the idea is the same.
Don't obsess over getting them perfect. +- 3% of zero and +-5% of each other is just fine.

 

[heavyD]

I focus on getting the STFT to 0 and don't really worry much about the LTFT although I think mine sits at -4...

I focus on keeping LTFT at 0 as the STFT will always change from -2 to +2 for example depending on the time of day and temperature. If your LTFT is constantly at or close to 0 that means that your low throttle setting is about perfect. STFT are great for initial tuning but it's the LTFT that you want to keep at 0.