Thoughts on CL with STFTs only... Esp for SD.
12-03-2007, 12:46 AM
#1
Thoughts on CL with STFTs only... Esp for SD. Hey guys...
I would like to hear of any long term setup that you have tuned that uses STFTs only for closed loop correction and any characteristics out of the ordinary that may have been encountered.
I ask about this after fighting severe fueling problems on a few SD tunes, more 2-bar tunes, but SD in general that is directly tied IAT heatsoak. I usually try to push the bias table around a bit, but generally have a hard time getting much of any good result like this. The bigger issue here, really, since the setups are all closed loop is the fuel trims swinging quite positive and screwing with WOT AFR. Also, as they learn fully positive, tomorrow when it's cold and we start up with it fat, some sensitive cams may not like it and those fat trims will be locked until it warms up and moves to closed loop.
Recently, I have moved my car over to STFTs (working well) so I have setup two others similarly. I should mention that I am using HPTuners.
The first case is a twin turbo (TTi X) vette with a 2-bar SD OS. The IAT sensor in it's intake pipe loves to heatsoak and make things nuts. This was a post-"finished" tune that it was tried on. After about 15-20 miles it seemed to work very well, but I will be meeting back up with the owner shortly to do some logging and review, so an update is a week or so away.
The second car I did this weekend like this, and it is N/A. I didn't have heatsoak issues, and this car was tuned with HPTuners MAF-Enhanced OS so that we could use real-time tuning with his stock PCM. The car is a 2000 A4 with a Yank pro extreme verter (4500, power adder stall) with a set of TEA stg 2.5 heads and a Cam Motion custom grind for this setup (ls6 intake also) 230/235 on a 112. It's a little nasty to get it dialed in for cold cold starts. Needs more IAC
I set the cut point for the full switch from VE to MAF (Dyn Airflow, high RPM disable) at 3200 RPMs and tune the VE from the bottom to 3600 RPMs. Once that is done, the MAF goes back in the mix and gets adjusted with the wideband across its scale to hit commanded fueling. On a last log plotting all AFR error against the MAF table, no cell was further out than 2% and 0-1 was seen through most cells. With it being this close, the car seemed to run really well in CL with just STFTs so that is how I left it. After driving for a day, I can't see why I need LTFTs at all since the tune is so close. Another plus is, if trims wander a bit positive, they never affect PE.
Now tell me as well if there is some reason that is right now not occuring to me to use LTFTs if the tunes are very close as well as any experience you have doing things similarly. Thanks guys.
I would like to hear of any long term setup that you have tuned that uses STFTs only for closed loop correction and any characteristics out of the ordinary that may have been encountered.
I ask about this after fighting severe fueling problems on a few SD tunes, more 2-bar tunes, but SD in general that is directly tied IAT heatsoak. I usually try to push the bias table around a bit, but generally have a hard time getting much of any good result like this. The bigger issue here, really, since the setups are all closed loop is the fuel trims swinging quite positive and screwing with WOT AFR. Also, as they learn fully positive, tomorrow when it's cold and we start up with it fat, some sensitive cams may not like it and those fat trims will be locked until it warms up and moves to closed loop.
Recently, I have moved my car over to STFTs (working well) so I have setup two others similarly. I should mention that I am using HPTuners.
The first case is a twin turbo (TTi X) vette with a 2-bar SD OS. The IAT sensor in it's intake pipe loves to heatsoak and make things nuts. This was a post-"finished" tune that it was tried on. After about 15-20 miles it seemed to work very well, but I will be meeting back up with the owner shortly to do some logging and review, so an update is a week or so away.
The second car I did this weekend like this, and it is N/A. I didn't have heatsoak issues, and this car was tuned with HPTuners MAF-Enhanced OS so that we could use real-time tuning with his stock PCM. The car is a 2000 A4 with a Yank pro extreme verter (4500, power adder stall) with a set of TEA stg 2.5 heads and a Cam Motion custom grind for this setup (ls6 intake also) 230/235 on a 112. It's a little nasty to get it dialed in for cold cold starts. Needs more IAC
I set the cut point for the full switch from VE to MAF (Dyn Airflow, high RPM disable) at 3200 RPMs and tune the VE from the bottom to 3600 RPMs. Once that is done, the MAF goes back in the mix and gets adjusted with the wideband across its scale to hit commanded fueling. On a last log plotting all AFR error against the MAF table, no cell was further out than 2% and 0-1 was seen through most cells. With it being this close, the car seemed to run really well in CL with just STFTs so that is how I left it. After driving for a day, I can't see why I need LTFTs at all since the tune is so close. Another plus is, if trims wander a bit positive, they never affect PE.Now tell me as well if there is some reason that is right now not occuring to me to use LTFTs if the tunes are very close as well as any experience you have doing things similarly. Thanks guys.
12-03-2007, 08:37 PM
#4
What you just described would certainly explain why my GTO starts better with stft's turned off than in closed loop. Everything works good except starting the car 20-30 minutes after it was last ran. Under those conditions it hunts for idle for a few seconds. In full open loop I don't have that problem. However, in my friend's Escalade with 2bar OS that I spent countless hours tweaking for different climate conditions, I have no such issue. I make changes to the GTO too often to spend that sort of time tweaking IAT bias and filter tables. In the Escalade with the turbo, I nailed down the VE and injector offsets, then any time the weather changed, I tweaked the IAT modifiers to get it right. This was done on many separate occasions over the course of most of a year. However, we still usually just leave it in full open loop. This keeps the possibility of a bad o2 sensor messing up the tune to a minimum. BTW, that Escalade just ran a 13.42 Friday night, which wouldn't sound impressive if the raceweight wasn't close to 6000lbs.
12-04-2007, 07:53 AM
#5
Long terms suck. Leave em off. If the VE is close, you dont really need them. At least thats my .02
Plus you have issues with big cam motors and the LTerms skewin things because of inconsistencies due to overlap.
I've seen cammed cars go from slightly positive (avg) to slightly negative (avg) in just a few minutes after dialing in the VE. So, long story short I just leave the long terms off.
Plus you have issues with big cam motors and the LTerms skewin things because of inconsistencies due to overlap.
I've seen cammed cars go from slightly positive (avg) to slightly negative (avg) in just a few minutes after dialing in the VE. So, long story short I just leave the long terms off.