question about tuning LTFTs on HPT.
question about tuning LTFTs on HPT. Hey guys, fairly new to tuning but i have a question, so i disabled my maf, turned the maf fail high to 0hz.. so i reset my FTs and drove it for about an hour to help them re learn the fuel curve, now heres where my question arises. I saw the values from the log, i then added them into the VE table. When i take the car back out again for tuning, should i re set the FTs once again and drive for an hour or can i just drive for some time re log and tune from there? Basically do I have to reset fuel trims everytime i modify the table and calibrate the ecm.
thanks.
thanks.
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From: Denver International Airport, Colorado USA
Using the 'other' software tuning suite here, but the concept is the same.
Trying to understand what stage of the tune are you at? Are you leaving it SD? Open loop or closed?
Normally doing AutoVe for SD you disable the Trims first. Otherwise your data will be biased from fuel be added or subtracted via Trims.
If you have already completed AutoVe and are going back to closed-loop and are using the Trims to 'finish' off the VE table, then yes you want to reset the Fuel Trims (LTFT's) each time you do a run. Only the LTFT's carry over various ignition cycles and miles/cells hit. You do not want them biasing the data.
One of the techniques I have used with some success is simply disable the LTFT's each run, but enable closed-loop and run off the STFT's. I will do this 2-3 times until it looks reasonable.
All depends on how you are going to ultimately run your car. You can really get into 'chasing your tail' syndrome real quick. One tune is off the wideband, one is using your narrowband O2's..until you forget what you were trying to accomplish. It can get really crazy as Trims change with weather, gas fill-up etc.
Hopefully I have not confused you. The simple answer is yes..re-set your Trims prior to each run.
Hope that helps..
..WeathermanShawn..
Trying to understand what stage of the tune are you at? Are you leaving it SD? Open loop or closed?
Normally doing AutoVe for SD you disable the Trims first. Otherwise your data will be biased from fuel be added or subtracted via Trims.
If you have already completed AutoVe and are going back to closed-loop and are using the Trims to 'finish' off the VE table, then yes you want to reset the Fuel Trims (LTFT's) each time you do a run. Only the LTFT's carry over various ignition cycles and miles/cells hit. You do not want them biasing the data.
One of the techniques I have used with some success is simply disable the LTFT's each run, but enable closed-loop and run off the STFT's. I will do this 2-3 times until it looks reasonable.
All depends on how you are going to ultimately run your car. You can really get into 'chasing your tail' syndrome real quick. One tune is off the wideband, one is using your narrowband O2's..until you forget what you were trying to accomplish. It can get really crazy as Trims change with weather, gas fill-up etc.
Hopefully I have not confused you. The simple answer is yes..re-set your Trims prior to each run.
Hope that helps..
..WeathermanShawn..
im trying to run the car in closed loop. Once the FTs look acceptable(+/-4) i was going to try and hook the maf back up and tune that? Still trying to learn all this tuning stuff.. 
I appreciate the help WeathermanShawn. One more quick question, how long do you guys think i should log for before I can shut it down and change the VE table? And should i smooth it when done? Thanks again.
TECH Enthusiast
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I usually can get it done on a 45 minute drive. If I get the right day I usually try to do it early morning when the temperatures are not changing that much.
Hopefully some others will give their input. Maybe a few can get all the cells they need even quicker, but under a hour is not bad.
..WeathermanShawn..
Hopefully some others will give their input. Maybe a few can get all the cells they need even quicker, but under a hour is not bad.
..WeathermanShawn..
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On The Tree
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From: Macungie PA
Once your happy with the values in the Primary VE table you should do some smoothing on some values so you don't have high leaps from cell to cell. That is one of the key things to always look for. If you have cell leaps above five it is always a good idea to use the smoothing button in HP Tuners. Good luck Bluestreak362 
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One time tasks:
- Create a custom PID that adds STFT and LTFT together.
- Create a custom histogram that uses the Primary VE vs RPM vs MAP for the table and the custom STFT+LTFT PID you created, and set the "cell hits required" value to 25.
Wash, rinse, and repeat tasks:
- Drive the car until the engine oil is up to temp (e.g. 110 Celsius). This step is important. Do not skip.
- Reset fuel trims.
- Start logging.
- When you are finished logging, view the "Average" values for the custom histogram you created.
- Copy the contents of the custom histogram
- Paste the values into Excel (or something similar).
- Search and replace any -1, -2, -3, or -4 values with null/blank (we do not want to the values in these cells to change as they are ideal).
- Search and replace any 0 values with 1. This step can be skipped and is more of a personal preference. Although 0 is the ultimate value I prefer a -1 to a 0 as your fuel trims will always swing a bit and a 0 does not leave much room before a positive fuel trim might be encountered (which is not ideal for PE).
- Copy this "new/massaged" table.
- Open up VCM Editor and navigate to the Primary VE table.
- Highlight entire Primary VE table, right click table and from the menu that appears select --> Paste Special --> Multiply by % - Half
- Save hpt file.
- Upload new config to vehicle.
- Repeat cycle.
The end goal is to have your fuel trims in the -1 to -4 range.
It is important to realize you cannot cover the entire VE table using the procedure above. Well technically you can but it is not advisable. Just do the lower portion (RPM <4000) and do the upper portion and PE portion with a wideband.
- Create a custom PID that adds STFT and LTFT together.
- Create a custom histogram that uses the Primary VE vs RPM vs MAP for the table and the custom STFT+LTFT PID you created, and set the "cell hits required" value to 25.
Wash, rinse, and repeat tasks:
- Drive the car until the engine oil is up to temp (e.g. 110 Celsius). This step is important. Do not skip.
- Reset fuel trims.
- Start logging.
- When you are finished logging, view the "Average" values for the custom histogram you created.
- Copy the contents of the custom histogram
- Paste the values into Excel (or something similar).
- Search and replace any -1, -2, -3, or -4 values with null/blank (we do not want to the values in these cells to change as they are ideal).
- Search and replace any 0 values with 1. This step can be skipped and is more of a personal preference. Although 0 is the ultimate value I prefer a -1 to a 0 as your fuel trims will always swing a bit and a 0 does not leave much room before a positive fuel trim might be encountered (which is not ideal for PE).
- Copy this "new/massaged" table.
- Open up VCM Editor and navigate to the Primary VE table.
- Highlight entire Primary VE table, right click table and from the menu that appears select --> Paste Special --> Multiply by % - Half
- Save hpt file.
- Upload new config to vehicle.
- Repeat cycle.
The end goal is to have your fuel trims in the -1 to -4 range.
It is important to realize you cannot cover the entire VE table using the procedure above. Well technically you can but it is not advisable. Just do the lower portion (RPM <4000) and do the upper portion and PE portion with a wideband.
