stft tuning instead of ltft tuning?

[wilson]

I am used to tuning Fords and am new to the GM vehicles. Normally, we shut off the ability of the ltft's, tune the stft then clear memory and turn ltft back on. Would this not work on the GM's? Next after the trims are done, make wot fuel adjustments with the maf instead of the PE table. Set the PE to your commanded afr by dividing stoich by 14.7.

Thanks for any positive input.

[MMGT1]

Attachment 2050


Under "VCM Controls" Click on Fuel and spark and then click Fuel trim learn ON and then reset fuel trims. This will lock the fuel trims so you don't have to reference the long and short. Makes things very fast and easy!!(looks like it is the same as the Ford to me)

Paul

[EC_Tune]

I always turn off the LTFT's when tuning both VE and MAF. Like you said, it's much easier to tune with the LTFT's off. They take far too long to learn into the correct values and gas is expensive...

Tune the VE table first then do the MAF. Move the VE & MAF to reach the commanded PE values. As always. Have fun doing it!

EC

[domestic rice]

Attachment 2050


Under "VCM Controls" Click on Fuel and spark and then click Fuel trim learn ON and then reset fuel trims. This will lock the fuel trims so you don't have to reference the long and short. Makes things very fast and easy!!(looks like it is the same as the Ford to me)

Paul

That sounds VERY easy. Even I understand it. Why was other advise given out to shut off this that the other thing, jump through two hoops ect....

Let me get this streight, to kill the LTFT so I can tune the STFT and get them in check, that is all I need to adjust/change?

[EC_Tune]

Clicking Fuel Trims ON will cause the LTFT AND the STFT to enable. Fuel Trims OFF should shut off the LTFT's and the STFT's stay enabled unless you turn them off in the editor or you turn Closed Loop Fuel OFF as well.

Regardless of your method, you should hit the Fuel Trim Reset button after making changes unless you have disabled the LTFT's in the editor previously.

[domestic rice]

I am just looking for the quickest way to get my fuel trims in check. I printed out the other directions about disconecting the maf and disabling sensors and the other thing. It lost me, so I decided to do the slow route of adjusting a little by little.

If what MMGT1 posted is all I need to disable to get to the STFT without the LTFT messing it up I am all about it!

[EC_Tune]

Remember just shut off the Fuel Trim Enable if you don't want LTFT data. If you shut off Closed Loop and Fuel Trim Enable, you're in open loop.

[5_Liter_Eater]

Why was other advise given out to shut off this that the other thing, jump through two hoops ect....

The only thing I know you need to turn "off" is to lowe the MAF fail frequency to 0 to tune the VE. Also you can't really get any upper RPM/load data with fuel trims because PE kicks in and locks the fuel trims. So tuning with a wide band and using % AFR Error is better. In that case you need to turn off closed loop operation.

PS: I ran into trouble trying to disable LTFTs via VCM controls. It didn't seem to work, at least on my LS1. I had much better luck disabling it in the tune.

[EC_Tune]

Yep, Some have a switch setting for STFT in open loop mode. If that's enabled, you get STFT's.

[domestic rice]

The strange thing is that on the histogram, my stft average is from 0 to -2, and my ltft average is from -6 to -11. If ltft gets its settings from the stft why is it so far off?

[EC_Tune]

LTFT is a Stored Look Up value for a particular operating range defined by the LTFT RPM & MAP points. The LTFT changes when the STFT goes beyond the boundaries set in the Open/Closed fuel tab. Usually +/-4-5% STFT. When the LTFT finally adjusts you will see the STFT go near zero as you have noted. And as long as you stay in that particular RPM / MAP range.

[r40734]

LTFT is a Stored Look Up value for a particular operating range defined by the LTFT RPM & MAP points. The LTFT changes when the STFT goes beyond the boundaries set in the Open/Closed fuel tab. Usually +/-4-5% STFT. When the LTFT finally adjusts you will see the STFT go near zero as you have noted. And as long as you stay in that particular RPM / MAP range.

From what I've seen in the VCM Editor, there are several ways to turn off the LTFT. There's actually an Enable/Disable dropdown menu in the Engine > Fuel Control > OL & CL tab. You could also just drop the Max ECT below your operating temperature. Etc. I've been considering using the Disable option so that I don't have to worry about the VCM Controls disconnecting during my drive time. Any reason why I shouldn't use this method?

On that same page, why would you use STFT in Open Loop Mode? Could this help determine how to set the PE mode? Or will this allow the STFT's to continue logging valid data into the table if you go into Open Loop mode during logging, therefore preserving a usable fuel trim table?