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Tonyrodz
Resident Resident
Not sure if you're familiar with rte 36 in Atlantic Highlands.
Tonyrodz's Tahoe Build Thread
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Snowbound
Jim
Sorry for the misunderstanding @Scottydoggs. I was referring to your first sentence, bank 2 lean. The fuel trim is subtracting 31% fuel which would mean that bank 2 is rich like you said in second paragraph. That’s all I meant. I don’t claim to know everything, I’m only trying to help. I apologize for adding confusion to the situation.
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Scottydoggs
Full Access Member
the main issue was the one bank being so far off.
its the long term thats +18, st is neg 31 cause its trying to make the long term right. so its lean, so the stft is trying to make it richer. (and failing to do so) if not for the flood water id be saying replace the up stream o2. cause a +18 ltft is vac leak territory 99% of the time, but that would show lean on both banks more than likely.
at least it dried up and went back to normal. alls well that ends well.
HiHoeSilver
Away!
swathdiver
Full Access Member
Something electrical got wet and either needs repair or drying out. Couple weeks ago we were cruising in the ocean surf and now something got messed up. Didn't have time today but we're not towing so its not urgent. It amazes me that with all the stuff underneath, nothing else gets ruined by water.
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Tonyrodz
Resident Resident
Don't you worry @Snowbound , we know you were just trying to help
. Wish you knowledgeable guys could give a class on this stuff, so us unknowledgeable guys could learn it! Good info 
Snowbound
Jim
Don't you worry @Snowbound , we know you were just trying to help
I guess we just have to agree to disagree. I still stand behind my comments. STFT is used for immediate adjustments based on the parameters, whereas the LTFT is a slower adjustment. The LFTF value is stored in memory and "learns" from the STFT. If the STFT shows an increasing trend, the LTFT will increase and allow the STFT to normalize and vice versa. If any of the value exceed 25% or -25% then the check engine light is turned on. LTFT and STFT will usually stay close to 0%, if everything is working as it should, which equates to no adjustment. A significant increase in STFT or LTFT from 0% means the ECU is detecting more air than expected and is adjusting fuel delivery with more fuel. A significant decrease in STFT or LTFT from 0% means the ECU is detecting less air than expected and is adjusting fuel delivery with less fuel. The ECU takes the STFT and the LTFT, adds them together and then adjusts base number from it. In your situation -31 + 18 = -13 so the ECU was taking away 13% fuel.
But typically when the STFT and LTFT start going in opposite directions, it’s due to a dirty or faulty MAF sensor but I’ve seen lazy O2 sensors do the same.
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Scottydoggs
Full Access Member
still dont change the fact that that o2 was reading lean......
not sure if you know the difference between a neg and pos numbers, you got your pcm jargon down good, but they are backwards when you read them, neg is rich, pos is lean. stft like you said is the correction of the ltft. so the stft -31 is adding the fuel back to change the the ltft +18 back closer to zero where in a perfect world is where it should read.
and that cel light you say will come on, it will come on for a lean condition if not a bad o2 sensor.
go pull a large vac line off any car, the ltft will go pos up to +16 or higher. thats a lean condition.
now have a stuck open injector and it will flood out with a large neg number.
or add to much to your maf file or injector file and it will be pig rich showing a high neg number.
i own a tuner. all my junk is tuned. modded regal gs, tahoe and my ss camaro, all tuned. so ive over shot and ****** up plenty changing things. having a wide band confirms most of your screw ups real fast when dealing with fueling.
and i have read till my eyes bled and lost hair over how all this works. im no pro tuner, but i get by just fine. hell even stepping up from the supercharged v6 to LS platform took some new learning on the tuning side or what and why you change things. the os has so many more tables to play with.
not sure if you know the difference between a neg and pos numbers, you got your pcm jargon down good, but they are backwards when you read them, neg is rich, pos is lean. stft like you said is the correction of the ltft. so the stft -31 is adding the fuel back to change the the ltft +18 back closer to zero where in a perfect world is where it should read.
and that cel light you say will come on, it will come on for a lean condition if not a bad o2 sensor.
go pull a large vac line off any car, the ltft will go pos up to +16 or higher. thats a lean condition.
now have a stuck open injector and it will flood out with a large neg number.
or add to much to your maf file or injector file and it will be pig rich showing a high neg number.
i own a tuner. all my junk is tuned. modded regal gs, tahoe and my ss camaro, all tuned. so ive over shot and ****** up plenty changing things. having a wide band confirms most of your screw ups real fast when dealing with fueling.
and i have read till my eyes bled and lost hair over how all this works. im no pro tuner, but i get by just fine. hell even stepping up from the supercharged v6 to LS platform took some new learning on the tuning side or what and why you change things. the os has so many more tables to play with.
HiHoeSilver
Away!
You are correct that negative is rich and positive is lean.
You are incorrect in saying that -31 is adding fuel. It is, as you said a rich reading, and the computer is taking fuel away to get back to stoich.
Not to be a smart-ass, but in summary...
Negative fuel trim = rich condition = taking fuel away.
Positive fuel trim = lean condition = adding fuel.
Your second statement is exactly right. A huge Vacuum leak means tons of extra air, a lean condition, and a positive fuel trim, because the computer is dumping a ton more fuel in to balance out the excess air to try and make stoich.
Snowbound
Jim
Thanks Silver. I’m not here to argue with anyone or to find out who’s junk is bigger so I didn’t want to keep jumbling up Tony’s thread. But STFT does not compensate for LTFT. I’m not a pro tuner either, but I was 3 ASE certificates from being a master tech (as I puff out my chest). But have let them lapse since I’m not swingin wrenches to put food on my table any longer (chest deflates).
https://thetuningschool.com/blogs/news/fuel-trims-the-tuning-process
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