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Erratic STFT and LTFT

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mnetwork

15+ Year Contributor
1,017
2
Feb 25, 2006
New Milford, New_Jersey
I have never been able to dial in my injectors the way I would like them. I have managed to get my LTFTs to a point where they are in a somewhat acceptable range, but the other night the went askew which bothered me. Currently, the only way I can even get the LTFT to be even CLOSE to acceptable is to play around with MAF Comp and watch Combined FT. I don't believe I should have to be playing with this feature this much since I am on a stock MAF. No matter what I do I always come up with something like this...

50hz - Little change. Usually add 1 percent or so.
150hz - -2.3hz
250hz - +16.4hz
400hz - 11.7hz

My MAF Comp graph always fits that general shape. It seems like when ever airflow is higher (but still below 3k rpm) my Combined FT's will shoot UP. They seem to not shoot as high once airflow had gone above 250hz. At around 150hz my Combined FTs are usually negative. There is are also points between 50 and 150 and between 150 and 250 that I wish I could adjust. Adjusting deadtime usually just causes me to move these sliders around, but they still require the same general shape.

I personally do not know what to make of this, any help would be greatly appreciated. I have no idea what to look at to rectify this. I feel like using MAF Comp is just a band-aid in this situation and even after all this work depending on Airflow, RPM, and TPS my Combined FT is all over the place.

I also had two side questions:
-Do LTFTs have any effect on Open Loop? I have always assumed no, but I have read that LTFTs effect Open Loop on a lot of other cars so I just wanted to verify this.
-How do STFTs move into LTFTs? There are times when I feel like it isn't just taking an average of STFTs rather it is working on some random time interval and when it hits that interval it just takes whatever the STFT is at the moment. I feel I have been able to manipulate the LTFT by playing with the throttle (thus changing the STFT) as soon as I see the LTFT start changing.
 
i notice that if I am crusing at say 2200rpm my stft will be like -2 and my lt will be 0 so if i lean it out a percent or two the st goes to 0 and the lt will stay 0 this is how i tuned my low rpms then i steadly leaned it out into boost sometimes my st does go erratic when i let off the gas i see -15 for a second then right back to 0. So from what i gather the st has direct effect on the lt if you cruise around at like 2200 rpm what ever adjustment you made at 2200 effects the st and the lt if your off the lt will change if your good it stays 0. I've done alot of research some say they cancel each other out like if your 3 st and -3lt thats 0 fueltrim but i dont see how that is possible. Idk if thats any help but thats my experiance. I have an afc though
 
do you have ECMLink setting? can you post a log? are you running MAF or SD? do you have MAF-T if you are on maf?
 
Here is a log with MAF Comp zerod... I feel like the numbers always go crazy when I'm on the highway and a go very light on the throttle (between 50 and 100ish hz) and when I get around 200ish hz...
 

Attachments

  • MAFCompZerod_Highway_and_Idle.elg
    151.9 KB · Views: 69
Anything ever come of this? I am kinda going through this issue now and found this thread but hoping to see the resolved answer.
 
Anything ever come of this? I am kinda going through this issue now and found this thread but hoping to see the resolved answer.

I wish I could say I did, but I really never got anything to make 100% sense. I wound up selling the car last summer. Different throttle positions at different RPMs yield too wide an array of trim numbers to get it all aligned perfectly... all on a stock 2g maf, i/m, and tb.
 
I wish I could say I did, but I really never got anything to make 100% sense. I wound up selling the car last summer. Different throttle positions at different RPMs yield too wide an array of trim numbers to get it all aligned perfectly... all on a stock 2g maf, i/m, and tb.

Gotcha, thanks for the update.
 
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