What exactly is the difference between LTFT's and STFT's? And which one do you use for reference when tuning the VE?

 

LTFT's are an average fuel trim learned by the PCM after observing the STFT pattern. If your LTFT's are within +/- 10, then turn them off and use the STFT's to tune the VE. Only do this for part throttle tuning where the car is commanding stoich. You'll need a wideband for the full throttle tuning.

 

After extensive part throttle VE tuning resulting in a smooth VE graph, is a wideband truly necessary for WOT tuning? I have read many tech articles saying this practice is acceptable, granted all LTFT's are within the range of 0 to -4.

 

Yes, because the car program will go into PE Mode and not reference the fuel trim values (if they are at zero), but base it's fuelling needs on the Stoich value vs. the PE multiplier. If it is off, you can be either too rich or lean. That is where the wideband comes in and helps you nail down you target AFR for best WOT performance.

 

If you tune without a wideband then you need to tunew using both LTFT and STFT...
its a combination...not one or the other
LTFT of -2 STFT of -4 for a total of -6
LTFT are Learned and remembered...STFT is momentary and forgotten

in HPT 2.0 I have built a histogram tat does this LTFT + STFT combo and its goes a lot quicker tuning VE
Most of the time I Use a wideband the entire time..but sometimes helping out with an e-mail tune I have to rely on LTFT/STFT gathered by the other person.

and you cannot get PE correct without a wideband..you can get it kind of close and safe..but not right on the money

 

Initially, yes you need to do this. However, if you want a finite VE tune, you turn off the LTFT's and use just the STFT's. Otherwise, you can get skewed averages going from one cell to another given it takes some time for the LTFT's to adjust. For example, if you're in FTC 4 at point A in the VE table where LTFT's are -6 and then move to point B in the VE table that's still in FTC 4, but has a +3 LTFT, there's a period of time where the LTFT's transition from -6 to +3. Maybe I notice that a little more because of EFILive's real-time dashboard. Tuning with just the STFT averages eliminates that transition time as well as saves the extra time/effort of adding in the LTFT's (as minimal as that effort may be) because they're all 0.

 

I second SpdDemon's point.



John.