Fuel Trims

[Devilish34]

Simple question right??

What am I looking for on my LTFT and STFT? - vs + ?? I assume Bank 1 and 2 should always be the same or real close? MAF gas?? Advance ??

Just trying to get and Idea what I should see on my DH now that my new tune is installed for my Vararam and Kooks.

[NYSS guy]

You want fuel trims to be just negative. If they are positive, you will run lean in PE mode (higher throttle %). Is that what you were looking for?

[Devilish34]

for the most part yes
Thank You

[NYSS guy]

Out of curiosity, what kind of fuel trims are you seeing?

[Devilish34]

I only installed my new tune last night so I really didn't to do to much. I think LTFT went from 0% to -5.5% and STFT @ idle around -3.9%. I log them today or if I go on the Dyno ask them to log it.

[UGotSmkd]

That seems to be about what mine shows. I know atleast one time, the values were flashing, but IDK what that was about.

[Devilish34]

That seems to be about what mine shows. I know atleast one time, the values were flashing, but IDK what that was about.

I pm'ed Charlie about them and they're Ok. They were just different from my other tune and wasn't sure what was what.

[johnh]

I like my LTFT to be -3% to 0% or so. You won't get them there though without some MAF tuning.

[TexasG8]

you want them to lock in at 0 during WOT

[Devilish34]

I like my LTFT to be -3% to 0% or so. You won't get them there though without some MAF tuning.

My previous tune (NEP side mount) LTFT was -5% normal driving -1.6% to 0% at wot . Kirk sent me a tune when I put my headers on that was a little lean at wot then sent me another on this past Monday. Tonight and this afternoon was around 3% at wot. Just the other day it would zero out at wot. I emailed some DH scans to Charlie to look at. Is there any where I can read up on this??

[johnh]

Search around the HPTuners forum and also there's some stuff on LS1Tech

[Devilish34]

Search around the HPTuners forum and also there's some stuff on LS1Tech

Thanks I keep wondering why my LTFT started out looking good at WOT but now hangs out around +3 to +3.9 @ wot
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[Paniller]

LTFT - long term fuel trim
STFT - short term fuel trim

Each is a percentage, + is fuel being added, - is fuel being pulled. So if you read -5 LTFT, your O2 sensor read 5% rich, and the computer knows to pull 5% from that cell to reach target A/F ratio.

Total fuel trim for that cell/condition can be thought of as the LTFT adjusted by the STFT. You just sum of the two, in theory. The LTFT is kinda the running average of STFT's. It'll start off at 0 if you just reset the computer. Then you'll see STFT's drop, and LTFT's increase. When the LTFT's stabilize, that's what people refer to as "learning the new fuel trim."

It's damn near impossible to hit 0 perfectly, so you'll want to err slightly rich to be safe, so slight negatives. These numbers only skew so far, so scanners max at +/-15 or so. So if you're seeing LTFT's settle at that number, the tune is off, and the computer can't add/subtract enough fuel to reach the desired A/F ratio, and your fueling is off.

Can't zero the LTFT's?
Pegged + values mean the engine is running very lean, and could also be caused by a vacuum leak/unmetered air into the engine. Pegged - values could be extra oxygen reaching the O2 sensor, or an exhaust leak.

That's what I know, from tuning my grand prix. I don't have a tuner for the G8, and am trying to keep the warranty. So, correct me if anything I said doesn't apply. I'm assuming it's similar regardless of car. We just seem to have two O2 sensors, so you probably want them balanced in terms of LTFT's as well.