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Tonyrodz
Resident Resident
Def gotta read this, seems to have good info. Thx.
Tonyrodz's Tahoe Build Thread
- Thread starter Tonyrodz
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Sam Harris
Supporting Member
Very interesting. Thanks!
HiHoeSilver
Away!
He's a smart dude. Lots of good videos. Haven't felt the need for his premium stuff yet.
Snowbound
Jim
My .02 for what’s its worth. The STFT adjusts according to info from O2 sensor for that bank. If the STFT has to keep adding fuel, the LTFT steps in and adds more fuel allowing the STFT to not have to adjust so far. There is a fueling table in the ECM that have cells. So at “X” RPM and “Y” manifold absolute pressure there’s a number for your base fueling. STFT do not make changes to that cell. They only adjust up or down from that number in that cell. When the STFT makes a change from that base number and stays more than 5% (in either direction) the LTFT steps in and makes that adjustment for the STFT to get it back under that 5%.
Example: STFT is adding 9% fuel for a preset time in ECM, LTFT says ok, you need more fuel so I’m gonna add 5%. Now your STFT is only gonna add 4% fuel to get that O2 sensor to read stoichiometric or perfect air fuel ratio.
The job of the LTFT is to keep the STFT as close to zero as possible. The O2 sensor reads lambda. Perfect AFR is lambda 1. Lambda 1 for gasoline is 14.68:1, E85 is 9.8:1, diesel is 14.5:1.
From what I see, your LTFT added 18% fuel because the ECM seen the STFT adding fuel for a length of time. Now the STFT is subtracting 30% fuel. That’s huge. Way out of its comfort zone. I’m my opinion, that’s an O2 issue. If it had a vacuum leak, or unmetered air, it should be adding fuel in the STFT.
When tuning, the first thing I do is disconnect the MAF sensor and disable it so it doesn’t set CEL. The ECM reverts to speed density meaning it reads air flow based off MAP. There are a lot of tables that effect fueling that use the MAF and you don’t want anything effecting the fueling while tuning. Then I reset the LTFT so they aren’t effecting my STFT. I want to know what the absolute value of each cell is while driving. You then log the STFT and watch how much fuel is being added or subtracted in the cells. You drive and try to hit as many cells as possible and you want at least 50 hits in each cell to get a good reading. After the drive, each cell is the average. It can be positive or negative. You take the data to the fueling table and multiply by %. In other words, if one cell was adding 20% fuel during the log, your taking the base number in that cell that’s preset in the ECM and multiplying it by the 20%. Then go for the next drive and log again, but reset the LTFT before you start logging. If you don’t, and the ECM seen a complete drive cycle, it’s gonna make the LTFT 20%. But you already added that 20% to the fuel table. So the next drive your gonna see the STFT trying to take away 20% and your gonna be scratching your head. Reset LTFT and drive. I tend to leave anything that shows 2% or less in the STFT alone. It’s not worth adjusting fuel table for 2%. That’s what the fuel trims will do.
Did any of that make sense? It’s late and I’m tired. My mind goes faster than my fingers so I hope I didn’t just confuse you more, as I’m not going back and proof reading this book.
Sent from my iPhone using Tapatalk
Example: STFT is adding 9% fuel for a preset time in ECM, LTFT says ok, you need more fuel so I’m gonna add 5%. Now your STFT is only gonna add 4% fuel to get that O2 sensor to read stoichiometric or perfect air fuel ratio.
The job of the LTFT is to keep the STFT as close to zero as possible. The O2 sensor reads lambda. Perfect AFR is lambda 1. Lambda 1 for gasoline is 14.68:1, E85 is 9.8:1, diesel is 14.5:1.
From what I see, your LTFT added 18% fuel because the ECM seen the STFT adding fuel for a length of time. Now the STFT is subtracting 30% fuel. That’s huge. Way out of its comfort zone. I’m my opinion, that’s an O2 issue. If it had a vacuum leak, or unmetered air, it should be adding fuel in the STFT.
When tuning, the first thing I do is disconnect the MAF sensor and disable it so it doesn’t set CEL. The ECM reverts to speed density meaning it reads air flow based off MAP. There are a lot of tables that effect fueling that use the MAF and you don’t want anything effecting the fueling while tuning. Then I reset the LTFT so they aren’t effecting my STFT. I want to know what the absolute value of each cell is while driving. You then log the STFT and watch how much fuel is being added or subtracted in the cells. You drive and try to hit as many cells as possible and you want at least 50 hits in each cell to get a good reading. After the drive, each cell is the average. It can be positive or negative. You take the data to the fueling table and multiply by %. In other words, if one cell was adding 20% fuel during the log, your taking the base number in that cell that’s preset in the ECM and multiplying it by the 20%. Then go for the next drive and log again, but reset the LTFT before you start logging. If you don’t, and the ECM seen a complete drive cycle, it’s gonna make the LTFT 20%. But you already added that 20% to the fuel table. So the next drive your gonna see the STFT trying to take away 20% and your gonna be scratching your head. Reset LTFT and drive. I tend to leave anything that shows 2% or less in the STFT alone. It’s not worth adjusting fuel table for 2%. That’s what the fuel trims will do.
Did any of that make sense? It’s late and I’m tired. My mind goes faster than my fingers so I hope I didn’t just confuse you more, as I’m not going back and proof reading this book.
Sent from my iPhone using Tapatalk
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Tonyrodz
Resident Resident
Wow, it's like high school algebra again lol. I was lost there too. So if I read correctly, it's like Scottydoggs said--most likely a wet O2?
HiHoeSilver
Away!
Here's something I posted before on the fuel trim topic for those of us that are a little "simpler" than guys like @Snowbound. And I don't mean "easier. Lol
The short terms are striving for stoich. The long terms are "more important" because they adjust based on what the short terms have been doing. If it sees the short terms adding fuel consistently, the long term bumps up so the short term gets closer to 0.
Lame analogy:
The short term guy is shooting free throws. His normal shot (0 trim) keeps falling short, so he shoots a little harder (5 trim) and starts making them (stoich). The long term guy says "we want your trim at 0“, so he moves the free throw line closer to the hoop (long term trim 5). Now the short term guy goes back to his normal shot (0 trim) and still makes it.
This is a constant game between the two. If the shooter starts launching them off the backboard, the long term moves the line back again. On and on. If the long term ever gets to +-25 it's gonna throw the rich or lean code for that bank.
In your case, the live data for the B2S1 (a graph would be best) may prove interesting as well.
The short terms are striving for stoich. The long terms are "more important" because they adjust based on what the short terms have been doing. If it sees the short terms adding fuel consistently, the long term bumps up so the short term gets closer to 0.
Lame analogy:
The short term guy is shooting free throws. His normal shot (0 trim) keeps falling short, so he shoots a little harder (5 trim) and starts making them (stoich). The long term guy says "we want your trim at 0“, so he moves the free throw line closer to the hoop (long term trim 5). Now the short term guy goes back to his normal shot (0 trim) and still makes it.
This is a constant game between the two. If the shooter starts launching them off the backboard, the long term moves the line back again. On and on. If the long term ever gets to +-25 it's gonna throw the rich or lean code for that bank.
In your case, the live data for the B2S1 (a graph would be best) may prove interesting as well.
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Tonyrodz
Resident Resident
Ok, so--Put my belt back on and took it for a ride. Just cruising down the road it was fine, floored it a few times and it was great. Live Data at 1500 rpms, sitting still
Sitting still at 2000 rpms
Ok, running great, so on the ride back it's fine--until I floor it. Reduced Engine Power came up. Reset it with the scan tool. Happens 3 times , each time while flooring it. I pop the hood and wiggle the tb plug, then unplug and replug--reset codes and floor it! Runs awesome again. Did that like 3-4 times--no cels. I'm thinking maybe plug wasn't seating good and everytime I floored it, the motor torqued, messing with the plug. I think @Scottydoggs hit it on the nose. Possible wet o2--or I'm hoping anyway. BTW--this was one of the puddles I hit.
I wasn't going slow either! Deepest part had to be at least 4-5" deep.
Sitting still at 2000 rpms
Ok, running great, so on the ride back it's fine--until I floor it. Reduced Engine Power came up. Reset it with the scan tool. Happens 3 times , each time while flooring it. I pop the hood and wiggle the tb plug, then unplug and replug--reset codes and floor it! Runs awesome again. Did that like 3-4 times--no cels. I'm thinking maybe plug wasn't seating good and everytime I floored it, the motor torqued, messing with the plug. I think @Scottydoggs hit it on the nose. Possible wet o2--or I'm hoping anyway. BTW--this was one of the puddles I hit.
I wasn't going slow either! Deepest part had to be at least 4-5" deep.
Did you ever fix that wire on the injector properly? Just thinking it might be contributing.
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Tonyrodz
Resident Resident
No, it is still heat shrunk tho. There wasn't any issues on the Live Data scan.
Won’t see it on live data if it’s intermittent unless you watch live data while you’re driving.
