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Lean?

D

Deeter

New member
I am pretty new to tuning but i have a quick question. I starting to do some wide open tuning and my 02 values are in the high 800's (875-890) which is sort of lean but the ltft are -12.5 which is telling the pcm to pull more fuel at WOT correct?

I can not decide what to do to correct this problem. Anyone know where i can start?

Thank you,

mods are intake and 3' downpipe, stock tune and 6kr (do to being so lean from the extra air?)
using a Powertuner
 


dont rely on the o2s. they are garbage unless you have a wideband. follow the fuel trims and the knock you are getting.
 
Maybe a stupid question but will fixing the LTFT ie by subtracting more fuel wont that make my o2 values go even lower?
Is there to some extent that a narrowband shows too rich or lean as an approximation?

if it makes any difference my STFT lock in at zero
 
the narrowband tells you absolutely nothing. it is different from car to car on what they read as far as good values. dont pay attention to that.

get your ltfts in check. the stft will always be decent.
 


Deeter said:
if it makes any difference my STFT lock in at zero
Click to expand...

That's because there is no STFT at WOT, so it will always be zero. STFT comes from instantaneous adjustments made by the PCM as a result of readings from the O2 sensor. LTFTs are the long term average of these so it knows where things "should" be. The O2 sensor is ignored in PE mode (WOT), so there is no STFT and it relies on LTFTs it figured out during the rest of your driving.
 
So correct me if I'm wrong, but since I want to go by my LTFT's instead of the narrowband O2 readings, should I lean it out since my LTFT's are at like -10? I really don't know if I'm supposed to add or subtract fuel. Well since negative LTFT's mean you're running rich and the PCM is pulling fuel I would think that you would lean it out, but my only concern is that the O2 readings were indicating that I was running lean. I know narrowbands aren't worth a ****, but if my car is really running lean and I lean it out more that would not be good. I'm confused and need help.
 
Smokin2000gtp said:
Well since negative LTFT's mean you're running rich and the PCM is pulling fuel I would think that you would lean it out, but my only concern is that the O2 readings were indicating that I was running lean. I know narrowbands aren't worth a ****, but if my car is really running lean and I lean it out more that would not be good.
Click to expand...

My thoughts exactly

From what i have gathered (not sure if i am right though):
Narrowbands are designed to read 14.7 AFR, any different and it can not read correctly. At WOT the AFR is say 12.4 (Stock) and lower depending on the PE Vs Time table so the narrowband is useless.

the negative LTFT at WOT the PCM based on the rest of the LTFT gathered under regular driving based off the 02 sensor reading 14.7 AFR.

we are running rich under normal driving so the computer assumes that we are going to be rich at WOT

To correct this we have to do MAF and/or VE tunes until the lifts become closer +3 to -3 under normal driving and when the PCM sees that the fueling is on under normal driving it will assume that fueling will be on for WOT and lock the LTFT in at zero.

Since I am so close to stock I think I will mess with the Maf and leave the VE alone until I get more modifications.
__________end what I gathered

new questions
If i get the ltft in line under normal driving and they lock into zero at WOT does it matter what the AFR is set at?

Can I set it a little lower say 12:1 in an attempt to kill some knock?

I know eventually that the commanded AFR table will eventually add timing for me so it cannot be set to low. Is there a safe AFR to set it at for a relatively stock car?

Please don't be afraid to tell me I am wrong this stuff is pretty new to me
 
Smokin2000gtp said:
So correct me if I'm wrong, but since I want to go by my LTFT's instead of the narrowband O2 readings, should I lean it out since my LTFT's are at like -10? I really don't know if I'm supposed to add or subtract fuel. Well since negative LTFT's mean you're running rich and the PCM is pulling fuel I would think that you would lean it out, but my only concern is that the O2 readings were indicating that I was running lean. I know narrowbands aren't worth a ****, but if my car is really running lean and I lean it out more that would not be good. I'm confused and need help.
Click to expand...

No, you don't want to lean it out. The PCM derives it's WOT LTFT from LTFTs during the rest of your driving. It does not use the O2 sensor during WOT. You need to do VE and MAF tunes to get your normal driving LTFTs as close to zero as possible. That'll bring your WOT LTFT back to zero, thus raising your O2s.

On the subject of the O2 sensor, it isn't useless. It's good for relative measurements. My 890 might not be as rich as your 890, but if I was seeing 890 and I'm now seeing 850, I know I'm leaner than before. See?
 
Sabrewings said:
On the subject of the O2 sensor, it isn't useless. It's good for relative measurements. My 890 might not be as rich as your 890, but if I was seeing 890 and I'm now seeing 850, I know I'm leaner than before. See?
Click to expand...

Good advice the narrow band o2 sensor is very helpfull and though it may not be the greatest way it's the way i have been doing it all along. You can get pretty close. I should wthout a doubt have a wide band by now and am going to be ordering one soon.


Anyway If you kept the stock tune wich you should have flash that back onto the pcm with the stock MAF table. Next reset the fuel trims then do a maf tune from 0 - 7500 hrtz on the MAF table hitting all the cells as many times as possible. three seperate drives of 30 minutes should do it. flash the new numbers after each 30 minute drive. This will take care of your fuel trims at idle and part throttle. This will get your car where it is suppose to be at...not lean not rich. Next move onto wot tuning. This really shouldnt be done without a wideband...but ANYWAY go wot and look at your o2's....you probably shouldnt run any less than around 940's being prety much stock...stock o2's are generally around 960's on a stock gtp.


Then if your to low on your o2's highlight the 7650 on up section and increase by a small amount. This is basicly tricking the pcm and saying that there is more air comming into the engine thus giving it more fuel. Flash and drive then go wot again and look at your o2's and adjust accordingly...simple as that and I can gurauntee that you wont have any problems doing it this way.


But you need to get real firmiliar with how the tuner works and how to use the histrograms. There your best friends in the long run. And it will make it a lot easier on your self if you do it this way.


And
 
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