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Thread: stft dont appear to work correctly, please help me understand

  1. #1
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    stft dont appear to work correctly, please help me understand

    I have been tuning a 99 dodge durango jtec 410 stroker and have the following issues. I have spent countless hours dialing in the fuel maps and have the vehicle running nearly perfect. I then set it to closed loop and the stft's are driving it lean, refer to datalog. The O2 sensor is showing lean but the stft is taking fuel out????? I have attached tune also. I am very confused and appreciate anyone's insight. vehicle will idles rough and stalls at coast down in closed loop. Thanks in advance for any help
    Attached Files Attached Files

  2. #2
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    check this video out. If your injector flow rate is right, then it's always about the air. If your lean and injector flow is right, you've got to much air.

    https://youtu.be/oULtX-NiKRE

  3. #3
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    Guys please help, I think this would be good learning for a lot of people and I know someone probably has some insight. If you look at the scan the O2 sensor is reading lean yet the pcm is pulling out loads of fuel driving everything lean? How is that possible? The STFT's are up to 12% negative? HP support has not been able to figure out

  4. #4
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    There's not enough info to give you any help with... The fuel trims from your log, don't show me a lean condition... It's taking fuel away... If you where lean, it would be adding fuel!!! you need to log o2 voltage and both banks STFT and LTFT... Actually drive the vehicle for awhile, your short log isn't going to expose the problem if any... As a matter of fact, from your log, it says you may not have fuel control... You gotta hit the accelerator to see how the S1 and S2 o2 respond to show us if you have fuel control first... Once you know you have fuel control, then, diagnose the symptom... You could have a slow o2 for all we know... best practce with fuel trim adjustment is to make an adjustment and drive it for a few hours... Dodge, Jeep, Ram require a lot of "fire cycles" to fill the cells... If you don't allow this, you will be chasing the fuel trims... When you adjust the Air by multiplying by the fuel, multiply by half, otherwise you will overshoot...
    Last edited by pointofview_365; 05-01-2021 at 04:21 AM.

  5. #5
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    Thanks for the reply. you are correct it is taking away fuel, but why? the O2 sensor is telling the computer it is lean, the wide band is showing lean, why is the PCM taking out fuel? I spent considerable time adjust the fuel tables to within +or - 3 % of the wideband. I then turned on closed loop and upon start it started driving it lean until it stalled. The wide band pegged lean. I have checked the plugs and it was definitely lean. I logged O2 voltage it is graphed on the bottom display along with the wideband showing lambda. As you can see when it started the wide band went above 1 lambda and the O2 dropped to below 200 milivolts (lean) yet the STFT's were going negative (also plotted on lower chart). That is my confusion. The 99 dodge only came with one o2 sensor thus showing only one bank. I will drive to drive the vehicle around but it is difficult in this state because the computer is driving everything lean. Before turning on closed loop I drove the vehicle for 400 miles and it performed perfect always staying within 3 of lambda with just a few exceptions. One interesting point is it seems to work once you get off of idle the stft's function properly. I will take further scans and post. Let me know if you do not see the line charts showing the O2, wdeband, STFT's plotted together. Maybe something messed up when I attached scans, I will verify I attached the correct ones. Thanks!

  6. #6
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    Just verified that I sent the correct scan. The charts below show
    I tried to send a snip of the chart but not working, Anyhow the upper line chart is plotting rpm, lambda, O2 volts and speed. The bottom chart is plotting Spark, tps, and STFT. As you can see I did blip the throttle and actually took it for a short drive, that is where you can see the PCM starting to work correctly off throttle. The last part of the scan was a coast down at which point it stalled. Thanks in advance for any help or suggestions. i will post some longer term scans today.

  7. #7
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    I'm away from my computer, doing my work , building stuff right now... The most important thing right now is showing you have fuel control, in my opinion. Go into WOT, IF your o2 sensor stays above 900 MV, you have fuel control. The stroker is adding more air than the OEM calibration, obviously you've accounted for already. CONCERNING!!! You definitely want to dial in your Stft and Ltft at part throttle first. I can only assume you've done that first without your adders... Then go for your Wideband at WOT later... Don't chase your tail... The wideband and O2 may never agree!!! Use the wideband for WOT and dial in your part throttle stuff first...

  8. #8
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    Okay, from what I'm seeing in the vcm editor and what you have available from a HP tuning stand point, you don't have the necessary Maps, tables to tune your 410 stroker... I'm not even seeing a VE map... What am I missing... I'm not familiar with a '99 ECU/PCM, so I'm ignorant how to help you without what I consider to be normal tunable stuff... If this is all the available stuff with HP, you might want to consider reaching out to a CMR tuner, Diablotoona is the only email tuner I would recommend... It could be me not understanding something here, but as of right now from your above calibration file, you've got nothing...

  9. #9
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    thanks to everyone's response. I decided to get the vehicle running and start driving before it died from lean. Once I got of idle the stft's worked in controlling 1 lambda. After driving for around 15 minutes the stft's started to work correctly at idle. Long story it is working now which I will take. Still confused why the PCM was pulling fuel out while everything was telling it the vehicle was lean. I would love to have the tables mentioned, unfortunately for my generation this is all that HP tuners offers.

  10. #10
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    kevhill, thanks for posting, with all your frustration. This way us new comers also learn and you got some assistance from pointofview.
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete