Dataloggin STFT and LTFT

[03mustang92]

Newbie question for tuning, but i got a custom tune on my 03 cobra and now when it idles, my lc1 indicates that it is running reallllly fat, like around 10.8. So i call my tuner and he said that the lc1's arent that accurate and its probably giving a false reading so datalog 1 LTFT and 2 STFT's with rpm and maf counts and get back to him.
Sent him an email but he probably wont be getting back to me till sometime next week, anyone else wanna take a look at it?
PM me and i will send u an email of the datalog

 

[mustangtw]

For stft and ltft when datalogging a value of 1.0 is perfect. Stft less than 1 is lean, need to add fuel to tune. More than 1 is too rich, need to subtract fuel in tune. Example: stft = 1.25 you are 25 percent rich and need to multiply ur maf transfer function by 0.75 to correct the rich condition. Hope that helps some

 

[2001Snake]

Send it to me sir. I'll help ya out!

[email protected]

Jay

 

[iggster]

For stft and ltft when datalogging a value of 1.0 is perfect. Stft less than 1 is lean, need to add fuel to tune. More than 1 is too rich, need to subtract fuel in tune. Example: stft = 1.25 you are 25 percent rich and need to multiply ur maf transfer function by 0.75 to correct the rich condition. Hope that helps some

Eeeekkk you have it all backwards....


1.25 means the computer is adding 25%, so the engine is running lean.

less then 1 is rich, more then 1 is lean.

Also a little more detail.

Say long term is 1.15 and short term is 1.20 then the car is actually 35% lean.

 

[iggster]

So i call my tuner and he said that the lc1's arent that accurate and its probably giving a false reading so datalog 1 LTFT and 2 STFT's with rpm and maf counts and get back to him.

The lc1 if mounted and installed correctly is accurate.


I dont trust long term and short term fuel trims when I get a car in to tune if I am just checking the tune.

Why? cause I have seen that commanded a/f is leaner or richer then what the car should be running it. I seen it with a local tuner that tuned a car and he was commanding 15.8 as lamba.

So even though the car was running lean the car would not throw a CEL.

Then when tuning you have to make sure adaptive is off, or you are just gonna be fighting the computer.

So much more involved and so little information giving to us about the you are running setup.

 

[03mustang92]

Send it to me sir. I'll help ya out!

[email protected]

Jay

Email'd!

 

[03mustang92]

Basically all it is, is a
steggy stage 4 ported blower

twin 340 lph fuel pump (-8 feed, -6 return) e85
off road x pipe
ba3000
jlt intake
dragon tb and plenum
80lb injectors
aeromotive fuel rails
egr elimated
maggy catback
its nothing much but i just want to have someone double check stuff

 

[iggster]

Do you have the x3 connected to the wideband to datalog?

email me a datalog file ill look it over.

RPM
A/F
ST fuel trims and LT
MAF counts

If you can do a datalog at idle then 2,500 rpm then 3,500 try and hold that rpm for like 5 seconds or so.

PS, Ive seen tuners disable closed loop and the fuel trims are always 1.00, had a customer come in once and was complaining about shitty gas mileage after a tune was put on the car.

Since those things are the things you seem more worried about.

[email protected]

 

[01yellercobra]

Isn't stoic for E85 9.85? Or is that just for WOT?

 

[mustangtw]

Eeeekkk you have it all backwards....


1.25 means the computer is adding 25%, so the engine is running lean.

less then 1 is rich, more then 1 is lean.

Also a little more detail.

Say long term is 1.15 and short term is 1.20 then the car is actually 35% lean.

U sure about that? I am pretty sure stft is opposite ltft. O.75 stft is lean meaning long term would go to 1.25 which would be adding 25percent more fuel to correct itself.

 

[iggster]

U sure about that? I am pretty sure stft is opposite ltft. O.75 stft is lean meaning long term would go to 1.25 which would be adding 25percent more fuel to correct itself.

100% sure. I tuned my car and tune out of my shop so I have to know sort of what I am doing or things go south fast oke: lol

You can simply google it.

Here I took this picture off the don lasota book. I don't really tune via fuel trims though I use a wideband.

 

[mustangtw]

I guess where I am confused is when it comes to adjusting the transfer function based on the stft reading. According to that excerpt from don lasota's book with a stft of .9 you would multiply by 1.1 to increase the air flow numbers which increases the fuel. What I don't understand is why would you be increasing fuel if it's already running rich? According to that article .9 would mean the computer is taking away 10% of the fuel due to a maf transfer that is shifted rich. If you multiply it by 1.1 then that would make it add more fuel. I'm lost :shrug:

 

[2001Snake]

The man is right with his statement. Above lambda is lean below is rich. I know because I've had these problems before.

Man I looked at your log and everything seems pretty good. You didn't log long term fuel trim bank 2 but judging by the short term on bank 2 it will be fine also. It is normal for the short terms to be a touch below lambda if lambda = 1.000. Everything looks good to me. I didn't have long to study it but I'd say your good!

 

[03mustang92]

ok cool, thank u 2001snake, the other ltft was datalogged in another file but it was very similar to the "already said" ltft, if that makes sense,
Thanks again 2001 snake

i was gonna datalog afr's but i was having issues getting the sct software to recognize the analog plug in

 

[encasedmetal]

I guess where I am confused is when it comes to adjusting the transfer function based on the stft reading. According to that excerpt from don lasota's book with a stft of .9 you would multiply by 1.1 to increase the air flow numbers which increases the fuel. What I don't understand is why would you be increasing fuel if it's already running rich? According to that article .9 would mean the computer is taking away 10% of the fuel due to a maf transfer that is shifted rich. If you multiply it by 1.1 then that would make it add more fuel. I'm lost :shrug:

you can adjust your maf xfer table based on stft's, but only if adaptive learning is turned off. it's much much easier and accurate to make changes to the maf xfer table based on open loop wideband readings. once these are dead on, your stft and ltft will follow suit, and you can turn adaptive back on and not worry about it anymore.

 

[mustangtw]

you can adjust your maf xfer table based on stft's, but only if adaptive learning is turned off. it's much much easier and accurate to make changes to the maf xfer table based on open loop wideband readings. once these are dead on, your stft and ltft will follow suit, and you can turn adaptive back on and not worry about it anymore.

Ok so with adaptive off and a stft of 0.90 i would add 10% more fuel by multiplying the transfer function by 1.1 which would then bring the trim to 1.0 correct? If this is the case then the engine was lean since i added fuel to it. If it was rich then i would be taking fuel out.

 

[encasedmetal]

Ok so with adaptive off and a stft of 0.90 i would add 10% more fuel by multiplying the transfer function by 1.1 which would then bring the trim to 1.0 correct? If this is the case then the engine was lean since i added fuel to it. If it was rich then i would be taking fuel out.

no. not to be rude but did you read through the thread and understand what stft readings are?
think of stft as an afr gauge (which they are, but narrowband, not wideband) and imagine that 1.0 is stoich (14.64 for unleaded gasoline). anything less than that (0.90 for example) is rich, just like 12.0 afr is less than 14.64 afr and is rich. anything over 1.0 and it's lean. hope that helps you visualize it. before you tune using stft I suggest you disconnect the battery, bring the car to temp and see what it's reading. over time the stft become the ltft and start over. this isn't changing your tune, it's changing the way your car runs while your driving. SO- to your original question, if your stft reading is 0.90 at 165 maf ad counts, and on your maf xfer table you have 155, and then 196 (just examples btw). you would multiply the 196 cell value by 1.0/0.90=1.1 bacause you are adding more air into the maf table to lean it out since you are getting readings of rich conditions. not adding fuel.

 

[mustangtw]

no. not to be rude but did you read through the thread and understand what stft readings are?
think of stft as an afr gauge (which they are, but narrowband, not wideband) and imagine that 1.0 is stoich (14.64 for unleaded gasoline). anything less than that (0.90 for example) is rich, just like 12.0 afr is less than 14.64 afr and is rich. anything over 1.0 and it's lean. hope that helps you visualize it. before you tune using stft I suggest you disconnect the battery, bring the car to temp and see what it's reading. over time the stft become the ltft and start over. this isn't changing your tune, it's changing the way your car runs while your driving. SO- to your original question, if your stft reading is 0.90 at 165 maf ad counts, and on your maf xfer table you have 155, and then 196 (just examples btw). you would multiply the 196 cell value by 0.90/1.0=0.90.

Thats not how the excerpt from the article above says how to do it. It says specifically if you have a 0.78 stft you multiply your transfer value by 1.22.

 

[encasedmetal]

Thats not how the excerpt from the article above says how to do it. It says specifically if you have a 0.78 stft you multiply your transfer value by 1.22.

I fixed it, I was basing my statement on fuel, not air, which is what the maf xfer table actually is. tis corrected now. however if you were using wideband readings you would definately use the 12.0/14.64 (again, theoretical numbers) and mult by that.

 

[DSG2NV03]

Maybe it is just me, but I trust the computer in closed loop (adaptive off) way more than I do a 200ish dollar wideband and I feel it is easier. Hate even relying on it in WOT, but I dont have thousands for a retarded expensive wideband.