LTFT's "Disabled"...good, bad, or otherwise???
02-14-2011, 09:47 AM
#31
The reason why that is preached so much is because the narrowbands do have a "deadband" of about 3%. What do I mean by "deadband" you ask? Well the reason for that term is because of the fact that the narrowbands do not switch until they are actually past the target which is stoich (lambda 1) thus the reason the switchpoints voltages are labeled Rich/Lean. You guys with hpt or efi live go out and take a log in closed loop and you clearly see in the chart view of the scanning where the O2s are switching just rich of stoich and then just lean of stoich, back and forth back and forth.
Now in open loop using a wideband you are no longer trying to hit a moving target. Ok I know what everybody is thinking and have seen it first hand no matter what happened tuning in open loop with the wideband when in closed loop the narrowbands take over and are doing their job which is keeping the fueling centered around stoich in which they do a very good job of that and are very accurate in doing so. The OEM has spent tons of time making sure of this especially these days with the emisions standards getting tighter and tighter. Now with that said I trust the narrowband O2s very much as long as they don't have a million miles on them and aren't 10 years old they are still very accurate. When you get some older ones with some miles on them they may not be switching like they should tuning evrything with the wideband is sounding even better to make certain that your commanded afr and actual afr are dead nuts on.
I was reading thru this thread and also had seen where it was brought up about the wideband and narrowbands not matching up and agreeing with each other. Yes definately a problem I have seen and have read many many many threads on the forums about. The first very important thing to make sure of is that the stoich afr table in the tune is set to match our wonderful ethanol blended fuels that is in our tanks these days. Because if this is set to 14.68, etc... which is the stoichiometric value for straight gas but their is E10 in the tank which is close to what you will find most places in the country these days which has a stoich value of around 14.1-14.2 that doesn't quite pan out. So if we have tuned all part throttle areas with our wideband to 14.7 which is what almost every wideband's stoich is defined as and then we go back to closed loop and now the narrowbands are going to be keeping the fueling centered around stoich for whatever fuel is in the tank. Obviously fuel trims could or will be off. I have proved this many times with some testing.
Like Atomic basically stated do we trust our wideband? With a decent wideband and a sensor that's not old and worn out I like to always think I can trust my wideband and I do and we also need to make sure we don't have any offsets between what the wideband is reporting and what we are seeing in the scanner which is important for things to match up.
One last thing that I don't think many tuners even know about or mess with is the Transport Delay or "flight time". The Transport Delay is the time from when the injector begins spraying fuel to when the O2 sensor applies a correction to the fueling. Now when we install longtube headers and we move the O2 sensors farther away from the factory stock location this adds about 25%-30% to the Transport Delay times. Correcting this by adding this 25% or so to the Transport Delay can help to bring things back in line.
Now that I am done with my rambling on and on I run with LTFTs disabled for the most part, the STFTs do the job of making the fueling corrections.
Everybody have a good day!
Now in open loop using a wideband you are no longer trying to hit a moving target. Ok I know what everybody is thinking and have seen it first hand no matter what happened tuning in open loop with the wideband when in closed loop the narrowbands take over and are doing their job which is keeping the fueling centered around stoich in which they do a very good job of that and are very accurate in doing so. The OEM has spent tons of time making sure of this especially these days with the emisions standards getting tighter and tighter. Now with that said I trust the narrowband O2s very much as long as they don't have a million miles on them and aren't 10 years old they are still very accurate. When you get some older ones with some miles on them they may not be switching like they should tuning evrything with the wideband is sounding even better to make certain that your commanded afr and actual afr are dead nuts on.
I was reading thru this thread and also had seen where it was brought up about the wideband and narrowbands not matching up and agreeing with each other. Yes definately a problem I have seen and have read many many many threads on the forums about. The first very important thing to make sure of is that the stoich afr table in the tune is set to match our wonderful ethanol blended fuels that is in our tanks these days. Because if this is set to 14.68, etc... which is the stoichiometric value for straight gas but their is E10 in the tank which is close to what you will find most places in the country these days which has a stoich value of around 14.1-14.2 that doesn't quite pan out. So if we have tuned all part throttle areas with our wideband to 14.7 which is what almost every wideband's stoich is defined as and then we go back to closed loop and now the narrowbands are going to be keeping the fueling centered around stoich for whatever fuel is in the tank. Obviously fuel trims could or will be off. I have proved this many times with some testing.
Like Atomic basically stated do we trust our wideband? With a decent wideband and a sensor that's not old and worn out I like to always think I can trust my wideband and I do and we also need to make sure we don't have any offsets between what the wideband is reporting and what we are seeing in the scanner which is important for things to match up.
One last thing that I don't think many tuners even know about or mess with is the Transport Delay or "flight time". The Transport Delay is the time from when the injector begins spraying fuel to when the O2 sensor applies a correction to the fueling. Now when we install longtube headers and we move the O2 sensors farther away from the factory stock location this adds about 25%-30% to the Transport Delay times. Correcting this by adding this 25% or so to the Transport Delay can help to bring things back in line.
Now that I am done with my rambling on and on I run with LTFTs disabled for the most part, the STFTs do the job of making the fueling corrections.
Everybody have a good day!
Finding a Non-ethanol blend is becomming very hard to do these days and alot of the tuning fluctuation is because of the varying blends.Thanks for posting up Klugg's SS!
02-14-2011, 02:54 PM
#32
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Great info. Thank you for posting. I was going to get into the STOICH vs ethanol blends on my first post however got interrupted at work and never remembered to get back to this topic Finding a Non-ethanol blend is becomming very hard to do these days and alot of the tuning fluctuation is because of the varying blends.
Thanks for posting up Klugg's SS!
Finding a Non-ethanol blend is becomming very hard to do these days and alot of the tuning fluctuation is because of the varying blends.Thanks for posting up Klugg's SS!
No problem man! I enjoy sharing some knowledge on here whenever I have some free time.
Yeah the idea of just pure ethanol free straight gas these days is really becoming non existent unfortunately and it can complicate things some in the tuning process. Which is also why people might see me on here preaching so much about thinking in terms of Lambda and using it to tune with, it can make things easier.
Lambda is just an excess air ratio and the mathematics of it remains the same no matter what you are tuning it could be alcohol, ethanol, gas, etc..... no matter what it is a Lambda = 1.00 is stoich. Alot well let me rephrase that most guys still use AFR and their isn't a darn thing wrong with that at all because ultimately you still end up at your end goal. I just find it much simpler using the other.
02-14-2011, 03:26 PM
#34
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The way I have it setup in hpt for scanning is I just have a couple of special PIDs made up for lambda and lambda error and usually once I do my check for any offsets between the wideband display and the scanner after that it's rare for me to even really look at the wideband, I just keep my eyes on what's being recorded in the scanner thru hpt.
02-15-2011, 07:03 PM
#37
Some more info on topic:
If ethanol (stoich AFR of 9) is mixed with gasoline (stoich AFR of 14.7) the resulting gas has a lower stoich AFR than 'pure' gasoline. As the fuel injection is tuned to mix a certain amount of fuel for a given amount of air, the resulting mixture would be leaner when using a fuel with lower stoich AFR.
This can be calculated:
sAFR = (%ofAdditive * sAFRadditive + (90-%ofAdditive) * sAFRgas) /100
where:
sAFR is resulting stoich AFR
%ofAdditive is amount in % of mass of additive (ethanol) mixed in
sAFRadditive is stoich AFR of additive (9 for ethanol)
sAFRgas is stoich AFR of base gasoline (14.7)
For a 10% mixture of ethanol to gasoline by mass the resulting stoich AFR is 14.13
So, for an engine that's tuned to certain AFR at a certain load and RPM on straight gas, the resulting (gasoline equivalent) AFR when running the mixture can be calculated as:
new AFR = tuned gas AFR * (gasoline stoich ratio) / blend stoich ratio
An engine tuned to 12.5 gas AFR will run at the equivalent of 13 gas AFR with a 10% ethanol blend.
Of course, when running in closed loop, the engine will run at 14.13 AFR instead of 14.7. O2 sensors (incl. widebands) don’t measure AFR, but Lambda. Lambda is defined as actual AFR/stoich AFR. It's a ratio. In closed loop part throttle the engine is just running at Lambda 1.0, regardless of fuel. The same would be true for other Lambda values when running closed loop at WOT using a wideband. The engine would run at the tuned Lambda and everything would be fine. Open loop systems would need to be retuned for alcohol blends though.
If ethanol (stoich AFR of 9) is mixed with gasoline (stoich AFR of 14.7) the resulting gas has a lower stoich AFR than 'pure' gasoline. As the fuel injection is tuned to mix a certain amount of fuel for a given amount of air, the resulting mixture would be leaner when using a fuel with lower stoich AFR.
This can be calculated:
sAFR = (%ofAdditive * sAFRadditive + (90-%ofAdditive) * sAFRgas) /100
where:
sAFR is resulting stoich AFR
%ofAdditive is amount in % of mass of additive (ethanol) mixed in
sAFRadditive is stoich AFR of additive (9 for ethanol)
sAFRgas is stoich AFR of base gasoline (14.7)
For a 10% mixture of ethanol to gasoline by mass the resulting stoich AFR is 14.13
So, for an engine that's tuned to certain AFR at a certain load and RPM on straight gas, the resulting (gasoline equivalent) AFR when running the mixture can be calculated as:
new AFR = tuned gas AFR * (gasoline stoich ratio) / blend stoich ratio
An engine tuned to 12.5 gas AFR will run at the equivalent of 13 gas AFR with a 10% ethanol blend.
Of course, when running in closed loop, the engine will run at 14.13 AFR instead of 14.7. O2 sensors (incl. widebands) don’t measure AFR, but Lambda. Lambda is defined as actual AFR/stoich AFR. It's a ratio. In closed loop part throttle the engine is just running at Lambda 1.0, regardless of fuel. The same would be true for other Lambda values when running closed loop at WOT using a wideband. The engine would run at the tuned Lambda and everything would be fine. Open loop systems would need to be retuned for alcohol blends though.
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