Short Term Fuel Trims How to read / interprete them ?

[Odan.be]

I need some info from the experts .
I am trying to fully understand logs, and the meaning of different parameters.
Because this is quite helpfull and essential when problem solving.

In this log : http://datazap.me/u/odanbe/trebila-r...ata=4-23-25-26

Fuel trims go quite low : just until -20% . Wich means to my understanding is the DME pulling back fuel , to stay around the AFR setpoint ?

The fuel used is ron 93/Oct 98.

But isnt -20% correction a lot ? and if this is too much.. what could be the cause ?
Is it a possible problem ? Or is it the nature of the tune ?

[Sticky]

I need some info from the experts .
I am trying to fully understand logs, and the meaning of different parameters.
Because this is quite helpfull and essential when problem solving.

In this log : http://datazap.me/u/odanbe/trebila-r...ata=4-23-25-26

Fuel trims go quite low : just until -20% . Wich means to my understanding is the DME pulling back fuel , to stay around the AFR setpoint ?

The fuel used is ron 93/Oct 98.

But isnt -20% correction a lot ? and if this is too much.. what could be the cause ?
Is it a possible problem ? Or is it the nature of the tune ?

Anyone want to give answering this a shot? I'll rep the $#@! out of you.

[bradsm87]

-20 still well within the usable range from -50 to +50. There is room for improvement with the 3D fuel scalar table to bring it closer to 0 though.

What are your mods? WGDC does look high for the boost. Stock downpipes?

[noorj]

20% correction really isn't abnormal, it just depends on what hard parts you've changed from stock that will effect this. Like Brad said, use the STFT %'s in your log to determine the changes to the 3d fuel scalar needed. I like to take half of the trim value and make that % adjustment to the VE (or fuel scalar in this case) for the specific speed/load. This will make you a nice and gradual walk of the STFT's from whereever they are to very close to zero in a couple iterations. That's where is becomes nice to have an automatic histogram plotter like some other platforms have

[alpinedevil335]

"Trims: Fuel trims (0-50). The Trims display shows what the STFT (Short Term Fuel Trim) signal is doing. This value is displayed as 25 = 0% trims, 50 = +33% trims, and 0 = -33% trims.

This signal can be quite variable but as long as it does not spend too much time pegged at 50 (maximum value) then all is well. If pinned at 50 for long parts of a run typically AFR will behind to lean out and tuning adjustments must be made to get fuel trims back within range.
　
This signal is used to calculate an automatically tuned variable FOL (Fuel Open Loop) or just OL (Open Loop) variable."

More info here...

http://www.n54tech.com/forums/showthread.php?t=21269

[noorj]

That's only for JB4, I assumed from the log this is not JB4 but just MHD tuning, correct OP?

[jyamona]

-20 still well within the usable range from -50 to +50. There is room for improvement with the 3D fuel scalar table to bring it closer to 0 though.

What are your mods? WGDC does look high for the boost. Stock downpipes?

STFT range is +/- 34%

[135pats]

As noted; important to understand that the JB scales it differently than you'd see from MHD/Cobb/BB Flash.

[bradsm87]

STFT range is +/- 34%

Thanks. I didn't know that. Stuck in JB4 way of thinking.