DaytonaBlues

I recently got my hands on a Launch CReader V and im trying to find out what the STFT ranges should be on a 1999 LS1 with a possible Predator tune done.
what ranges should i be looking for in both positive and negative %?

sorry for a newbie question but i know how important STFT and LTFT is and i just want to know what i should be seeing on a car with minor mods. any help would be greatly appreciated!
ill have to post what my readings are now once i get a solid idea of exactly what im getting both LTFT and STFT ill post, but a baseline idea would be great!

Sarg

iTrader: (6)

Within 5% of zero either way.

DaytonaBlues

Your kidding right? At idle my STFT both banks vary from -1.89% to +2.5%. During cruising graphing the STFT bank 1 or 2 I'm seeing -12% to +18%. Now that's the peaks I see on the scan tool as I'm graphing the datastream. I guess at idle its usual stable at -1.5% to maybe sometimes +3%. I'm just wondering what STFT would be at idle in CL at operating temp. On the open road is when I get wild STFT fluctuations from as low as -18% to as high as +20%.
My LtFt is usually stable at -1.5% around there.
Thanks fir any other help or some useful links since I do not have a tuner with a car that does need one.

Exidous

iTrader: (11)

If your STFT's are swinging +/-20% while at a constant state I.E. steady TPS and RPM the STFT should be +/-5% at worst. With your LTFT as close to zero as possible. The STFT drive LTFT over time. I do find it odd that that your O2's are causing your STFT's to swing that much. I get +/-18% while transitioning to on or off throttle but not steady state.

If you are good at idle then your MAF/VE table good at that spot. Anywhere else that isn't good needs tuning. All VE tuning need to be done at a steady state. A loaded dyno is best. WOT can help with a few cells in the VE and the MAF from about 4kHz and up.

Sarg

iTrader: (6)

STFT + LTFT on a good tune should be +-5% throughout the rpm range. If it is not, chances are neither are your open loop portions of the map. STFT is going to bounce around a good bit as you accelerate and decelerate, etc. But if it is a constant number while you are in a steady state, then it is obviously off in that particular cell in the tune. Provided that when you add STFT+LTFT < 5% whiile in a steady state then I would not worry about it. I THINK these ecus add the two. I don't know, the few that I have tuned with MAF I turned off long term fuel trims during the MAF tuning process.

DaytonaBlues

hey thanks for that help. sorry bout that but yes at a steady RPM (1500 in this case) my STFT are pretty good i think. Im getting a jump from -4% to plus 3ish, so from what you and the other fella said i think im good. my LTFT is -1.57% on both banks all the time, so adding that to my STFT i think im ok.
just to confirm as long as my STFT for bank 1 for example is within -+5% im good? Holding the rpm at 2 grand i get no higher than 3 or 4% positive and the same negative. while driving around i see wild STFT numbers, on my graph scan tool shows peak of nearly positive 22% and negative 15%, but like you said thats driving at varied rpm, map, tps etc.

Sarg

iTrader: (6)

You will get some pretty big fluctuations in STFT. As long as they do not stay over +-5% when in steady state it is no big deal. But if you have a LTFT of 5% and the short term is -7% in steady state, it just means conditions may have changed and it is now pulling fuel back out. Your LTFT will gradually adjust back down closer to zero.

Think of LTFT as learned fuel trims and STFT as instant fuel trims. After an ecu sees a +5% STFT for so many counts it will store that in to its long term fuel trim memory.

Exidous

iTrader: (11)

Your O2 sensors should be switching between max and min voltage while cruising. This will cause your STFT to change accordingly. As long as the average cancels the swings out you are fine. -1.57% on the LTFT is not bad at all. As long as it stays there you are fine.