STFT VS. LTFT

hairytool · Post by **hairytool** » Sat Dec 15, 2007 11:57 pm

What is the diference between STFT and LTFT? How does one effect the other? When I adjust the injector slope for LTFT will they automaticly coinside with each other

Post by **06MonteSS** » Sun Dec 16, 2007 2:21 pm

STFT are the short term fuel trims.. those are the instant/live adjustments that the ECM is making right at that particular time...

the LTFT's are the learned fuel trims over time...

adjusting the slope will affect both, but we don't care about the STFT's... need to see what the LTFT's are doing, because that's what the EDM uses to base it's fueling adjustments on.

Jruss · Post by **Jruss** » Sun Dec 16, 2007 2:31 pm

What are the dangers of having the LTFT's out of range?

Post by **06MonteSS** » Sun Dec 16, 2007 2:48 pm

depends on which way they are out of range... the ideal range is 0 to -2... but +2 to -2 is also an acceptable range...

if they are extremely positive, that means you are extremely lean... which means you will also be very lean at WOT... bad

if they are extremely negative, you are very rich... which will contribute to poor mileage, and increased engine load which will also adversely affect your auto tranny shifting...

in either case, it will affect throttle response, acceleration, etc etc...

ssheets · Post by **ssheets** » Sun Dec 16, 2007 4:02 pm

I had postive 8.25 on both banks. I subtracted 8% from my injector slope and 8% from my fuel setting. I thoughts that the way the instructions read...am I going the right direction or am I leaning it out even more?

"Determining long term fuel trims:
Long term fuel trims are an accumulated value of fuel added or subtracted during closed loop operation.
To verify and tune for long term fuel trims, drive the vehicle for 30 minutes or until warmed up, monitor long term fuel trims and get an average value. The easiest way to do this is to get on the highway, enable cruise control and sit at 55mph while monitoring the data. Ideal values should be in the 0 to negative 2 range.
Once you get the average long term fuel trim value:
Positive long term fuel trims For a positive value you subtract that value in percent in the predator injector slope. It is also recommended to lean both fuel tables by the same percentage."

This seems counter intuitive. According tho this I decrease my injector slope to increase or enrichin my fuel ratio. I'll get another LTFT run and see where it is.

Post by **06MonteSS** » Sun Dec 16, 2007 4:16 pm

if your average ltft's were 8.25, then set your injector slope to -9%. and i normally leave my PE fueling settings at 0....

I figure, if the ltft's are dialed in and the part throttle fueling is correct to maintain the stoich 14.75 AFR, then the WOT should also be in check now that we changed how much fuel the injectors are spraying...

so, with my ltft's dialed in and getting 0 to -2, I leave my PE fueling settings at 0 - and at WOT, my AFR is 12.6 to 12.8x...

hairytool · Post by **hairytool** » Sun Dec 16, 2007 4:31 pm

My LTFTs were off by 2-3% from bank to bank. Is this normal? bank#1 = 11.28 and bank#2 = 9.52 I subtracted 10% from injector slope and that put both LTFTs in the 0>- 4 range but bank#2 is still 2% less than bank #1!!

Post by **06MonteSS** » Sun Dec 16, 2007 4:32 pm

yeah, both banks won't be exactly the same....

if you're at 0 to -4, try bringing up the slope a couple so that you get in the +2 to -2 range...

hairytool · Post by **hairytool** » Sun Dec 16, 2007 4:44 pm

Cool, thanks! Also i noticed that the timing goes above 50deg and stays when reving the engine past 2 grand. It seems like alot to me but i get no KR=0.00%

ssheets · Post by **ssheets** » Sun Dec 16, 2007 10:36 pm

-8% on the injector slope was too far. I went to -4% and it looks right on. I'm maintaining 0 to +2.34 now.

Post by **06MonteSS** » Mon Dec 17, 2007 7:43 am

what?? how'd you get from +8 ltft's and slope set to -8%, to only needing a slope of -4%???

sounds like something wasn't read right or allowed to settle-in/relearn initially....

well, cool... least ya got it figured out....

Jruss · Post by **Jruss** » Tue Dec 18, 2007 7:13 am

06MonteSS,
Once we finally get everthing in tune, can we forget about the tuner until we make a changes or there is a new tune available?
How offen are you running logs on your vehicle?

ssheets · Post by **ssheets** » Tue Dec 18, 2007 3:13 pm

ssheets wrote:-8% on the injector slope was too far. I went to -4% and it looks right on. I'm maintaining 0 to +2.34 now.

Probably the vacuum leak that was throwing things off.

With Jesse's tune it now runs consistant at +6-8 on the LTFTs. He said not to worry about it and that these are good numbers to work with his OS and tune.

The car runs great and drives almost like stock.

pozzo · Post by **pozzo** » Mon May 26, 2008 12:22 am

06MonteSS wrote:if your average ltft's were 8.25, then set your injector slope to -9%. and i normally leave my PE fueling settings at 0....

I figure, if the ltft's are dialed in and the part throttle fueling is correct to maintain the stoich 14.75 AFR, then the WOT should also be in check now that we changed how much fuel the injectors are spraying...

so, with my ltft's dialed in and getting 0 to -2, I leave my PE fueling settings at 0 - and at WOT, my AFR is 12.6 to 12.8x...

I checked my ltfts (05 Corvette) and they were +7 so I dialed in -8. The ltfts were then fine but the AFR at WOT was about 18; very lean. I don't think you can assume that because your ltfts are on target that your AFR at WOT will be in range. I changed the PE to +4 to make it richer but have not rechecked the AFR at WOT yet.

Post by **06MonteSS** » Mon May 26, 2008 7:34 am

no, your AFR is not 18... You are fine - I wouldn't have changed the PE setting...

it's a known issue with certain vehicles/predators... in the Dataviewer, with your log loaded, go to VIEW > PARAMETER MODIFIERS > EQUIVALENCE RATIO-INVERT.... this will invert the AFR data and show the correct values.

STFT VS. LTFT

STFT VS. LTFT

RE: STFT VS. LTFT