Does this make sense?
11-01-2007, 01:25 PM
#1
Does this make sense? Tuning in closed loop isn't as productive as tuning in open loop with a WB. I'm not saying its wrong but it takes a while to get the LTFTs to 0 because you are actually fighting LTFTs and STFTs to get it there. In open loop there are no LTFTs or STFTs to fight. Using a wideband you can measure the complete AFR error without the fuel trim factors, thus allowing you to make stronger/closer adjustments.
WOT fuel trims will always be 0 because the O2 sensor information is not read by the computer while going WOT even in closed loop. Reason for this is the O2 sensors can't actually read the fuel when it is rich, only when lean so oddly you are tuning WOT in Open Loop weather you like it or not heh.
There is a failsafe that richens up WOT when your cruise LTFTs are too lean across the board, fooling the computer into thinking it must be lean at WOT. So if there are lots of +4 +5 in the LTFTs for cruising, most likely it will transfter to WOT.
Tuning WOT is actually quite easy too, you plug in the number you want into your PE, like if you wanted 12.8s across the board you plug in 1.148 (you get it by14.7/12.8) and that is your PE factor. Then you modify VE and MAF so when going WOT it reaches that level correctly.
Some people tune backwards and modify PE to get their AFR where they want it. This is what the predator and other handhelds do. It gets the same result, but is a backwards way of getting to it.
WOT fuel trims will always be 0 because the O2 sensor information is not read by the computer while going WOT even in closed loop. Reason for this is the O2 sensors can't actually read the fuel when it is rich, only when lean so oddly you are tuning WOT in Open Loop weather you like it or not heh.
There is a failsafe that richens up WOT when your cruise LTFTs are too lean across the board, fooling the computer into thinking it must be lean at WOT. So if there are lots of +4 +5 in the LTFTs for cruising, most likely it will transfter to WOT.
Tuning WOT is actually quite easy too, you plug in the number you want into your PE, like if you wanted 12.8s across the board you plug in 1.148 (you get it by14.7/12.8) and that is your PE factor. Then you modify VE and MAF so when going WOT it reaches that level correctly.
Some people tune backwards and modify PE to get their AFR where they want it. This is what the predator and other handhelds do. It gets the same result, but is a backwards way of getting to it.
11-01-2007, 01:43 PM
#2
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When tuning PE you are making the assumption that your VE table and MAF have the car running at 14.681 (14.7 stoich). If your VE and MAF aren't getting stoich then your PE multiplier will not get the desired 12.8 (ish) range either. So it is best to verify stoich operation BEFORE going after PE.
The half *** tuners just try to get PE to read approx 12.8 and ignore their "normal" stoich operation.
The half *** tuners just try to get PE to read approx 12.8 and ignore their "normal" stoich operation.
11-01-2007, 02:04 PM
#3
What do you mean by this "The half *** tuners just try to get PE to read approx 12.8 and ignore their "normal" stoich operation."
If you set the PE table to your commanded air fuel ratio value (well, actually equilivence ratio in GM applications) then that i what the pcm is commanding the airfuel ratio to be. (provided there is no long term correction, or COT altering this value) The PE table has nothing to do with stoich closed loop operation.
When tuning, you need the following things:
First assumption is your fuel flow model is correct, (stock vehicles it is correct) and then you can set your target values (PE mode) for airfuel.
Then you adjust your airflow model (either VE table, or MAF, or Both depending on how your tuning) so your wideband is equal to your commanded airfluel value.
Personally, I disable longterm learning when I start tuning, and use just the short term trims, In closed loop, you want them to be close to 0, if your wideband is a few points off (14.5 instead of 14.7) that's ok, since the narrow bands are what is going to be keeping the trims inline, and you dont' want to increase other trim drifting when your going by your $50 wideband sensor vs a $100 narrowband sensor to determine stoich of the fuel your running)
Once you get the airflow model correct, you can start with timing. If you want to verify your airflow and fuel flow models are correct, you can change your PE target, and see the actual airfuel at the wideband change. As a reality check, set the PE to 12:0 and 12.5 to verify.
WOT tuning is the easy part.
Ryan
If you set the PE table to your commanded air fuel ratio value (well, actually equilivence ratio in GM applications) then that i what the pcm is commanding the airfuel ratio to be. (provided there is no long term correction, or COT altering this value) The PE table has nothing to do with stoich closed loop operation.
When tuning, you need the following things:
First assumption is your fuel flow model is correct, (stock vehicles it is correct) and then you can set your target values (PE mode) for airfuel.
Then you adjust your airflow model (either VE table, or MAF, or Both depending on how your tuning) so your wideband is equal to your commanded airfluel value.
Personally, I disable longterm learning when I start tuning, and use just the short term trims, In closed loop, you want them to be close to 0, if your wideband is a few points off (14.5 instead of 14.7) that's ok, since the narrow bands are what is going to be keeping the trims inline, and you dont' want to increase other trim drifting when your going by your $50 wideband sensor vs a $100 narrowband sensor to determine stoich of the fuel your running)
Once you get the airflow model correct, you can start with timing. If you want to verify your airflow and fuel flow models are correct, you can change your PE target, and see the actual airfuel at the wideband change. As a reality check, set the PE to 12:0 and 12.5 to verify.
WOT tuning is the easy part.
Ryan
11-01-2007, 03:00 PM
#5
He may not be saying it is poo, but he is saying that you do need to verify that the other values will get stoich before going WOT (into PE mode) . Well, this is true as well, since the PE mode acts as a multiplier to the commanded airfuel value.
I do closed loop tuning (which will verify stoich) up to about 4000-4500 rpms on the loaded dyno, so that will cover most all of the driving around drivability. Using your trims to get the data back inline.
However, if your data is not 100% accurate before wot tuning, once you change the MAF/VE at wot, those points should get the proper stoich value as well. (assuming your fuel model is correct, since the PE works as a multiplier)
Ryan
I do closed loop tuning (which will verify stoich) up to about 4000-4500 rpms on the loaded dyno, so that will cover most all of the driving around drivability. Using your trims to get the data back inline.
However, if your data is not 100% accurate before wot tuning, once you change the MAF/VE at wot, those points should get the proper stoich value as well. (assuming your fuel model is correct, since the PE works as a multiplier)
Ryan
11-01-2007, 03:33 PM
#7
Well then does this make sense?
You are somewhat right, I could be just misreading your post so I'll explain.
The thing is that you should actually put in PE first because PE does not get "tuned". The common mistake for example is to start with those factors 1.148 to get a 12.8 and when you are getting a 13.1 you change the PE factor. You should not change the PE factor after setting your desired AFR. At this point you should be tuning your VE and MAF at WOT in order to find that stoich value.
The reason that works is because the car commands 14.7 at all levels except when in PE mode (close to WOT), which then it will aim for that 12.8 or so. So by tuning your VE and MAF to meet the 12.8 while commanding a 12.8 you have essentially found that "stoich" value.
When I first started, I tried tuning just PE to get the correct AFR... I built complicated Excel sheets in order to help aid me in my quest for the right AFR, then I found out I was doing it backwards.
You are somewhat right, I could be just misreading your post so I'll explain.
The thing is that you should actually put in PE first because PE does not get "tuned". The common mistake for example is to start with those factors 1.148 to get a 12.8 and when you are getting a 13.1 you change the PE factor. You should not change the PE factor after setting your desired AFR. At this point you should be tuning your VE and MAF at WOT in order to find that stoich value.
The reason that works is because the car commands 14.7 at all levels except when in PE mode (close to WOT), which then it will aim for that 12.8 or so. So by tuning your VE and MAF to meet the 12.8 while commanding a 12.8 you have essentially found that "stoich" value.
When I first started, I tried tuning just PE to get the correct AFR... I built complicated Excel sheets in order to help aid me in my quest for the right AFR, then I found out I was doing it backwards.
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11-02-2007, 01:33 AM
#8
technically you are tuning PE by just commanding a different WOT AFR from OEM 
I usually use 12.0 for N/A, 11.0 for SC, and 10.6-10.8 for turbos (this is general, setups vary) while I get the VE/MAF in line on the street. Once I am getting commanded AFR (really doesn't take too long, especially with HPTuner's real time tuning), it's off to the dyno to find out what AFR it likes most.
I usually use 12.0 for N/A, 11.0 for SC, and 10.6-10.8 for turbos (this is general, setups vary) while I get the VE/MAF in line on the street. Once I am getting commanded AFR (really doesn't take too long, especially with HPTuner's real time tuning), it's off to the dyno to find out what AFR it likes most.
11-02-2007, 07:54 AM
#9
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JS
Most people who tune set the commanded A/f ratio to the value they want then tune the VE. After the VE is good then tune the MAF.
Do you use the histograms? I add the long and short trims together. Then tune the VE both in open and closed loop. After the VE is good I reenable the MAF. Then I have a histogram for closed loop that logs fuel trims and MAF Hz. (when the command A/f is above 14.2). I have addition histogram that logs data when the A/F is less than 14 that is used for open loop.
Most people who tune set the commanded A/f ratio to the value they want then tune the VE. After the VE is good then tune the MAF.
Do you use the histograms? I add the long and short trims together. Then tune the VE both in open and closed loop. After the VE is good I reenable the MAF. Then I have a histogram for closed loop that logs fuel trims and MAF Hz. (when the command A/f is above 14.2). I have addition histogram that logs data when the A/F is less than 14 that is used for open loop.
11-02-2007, 11:37 AM
#11
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Lets see if I can explain this again.
In ideal operation your stoich value should equal 14.681, lets call it 14.7
To get the "ideal" PE ratio of 12.8 your PE should be 1.148 (give or take) (14.7/12.8)
Now say your PE is set to that 1.148 but your car runs rich when not in PE, and has an actual AFR is 13.7, (13.7/12.8) your actual AFR during PE will be 11.9 not 12.8. A half assed tuner would simply change the PE from 1.148 to 1.07 to get 12.8 (13.7*1.07=12.8) the problem with this is your normal operation is still rich.
If you get your VE and MAF to run stoich (14.7) getting the PE table correct is easy and quick.
In ideal operation your stoich value should equal 14.681, lets call it 14.7
To get the "ideal" PE ratio of 12.8 your PE should be 1.148 (give or take) (14.7/12.8)
Now say your PE is set to that 1.148 but your car runs rich when not in PE, and has an actual AFR is 13.7, (13.7/12.8) your actual AFR during PE will be 11.9 not 12.8. A half assed tuner would simply change the PE from 1.148 to 1.07 to get 12.8 (13.7*1.07=12.8) the problem with this is your normal operation is still rich.
If you get your VE and MAF to run stoich (14.7) getting the PE table correct is easy and quick.
