Is 1.20 LTFT bad lean condition and/or fuel problem or normal ?

Discussion in '2005+ Mustang GT 4.6L Tech' started by Mustangk, Mar 4, 2021.

  1. Mustangk

    Mustangk Junior Member

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    so i have stft that hover around .9 and then my ltft is at 1.20 which if im not mistaken means 20% correction to add fuel.

    how does ltft work on my sct x4. i want to understand what 1.20 means for ltft as i understand the stft of 1.00 is perfect and mine hovers around .9 but the ltft will start at like 1 and slowly go up and then stay at 1.20

    i used to get p0171 and p0174 but changed my bbk cai back to stock intake and it stopped.

    also installed new jba shorty headers but i believe the trims were the same prior to header install
     
  2. Dino Dino Bambino

    Dino Dino Bambino I have a red car

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    Did you run into any problems with the installation of JBA shorty headers?
    An LTFT of 1.20 indicates a lean condition. Are you getting the same reading from both cylinder banks? Some data logging might help to pinpoint the problem.
     
  3. Juice

    Juice forum member

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    1.20 means the PCM is adding 20% fuel to reach the correct AFR. LTFT is long term learned. STFT is the short term, or instant correction. Over time LTFT learns, and STFT will be closer to "1". A value of 1 means no correction needed. A stock and proprely operating car will have both of those at +/- 5% (.95-1.05)

    If it is on ONE Bank only, could be as simple as a bad O2 sensor on one side.
    If it is BOTH banks, it is an indication of a lean condition for whatever reason. But it will be an issue common to both sides.
     
  4. Mustangk

    Mustangk Junior Member

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    Well heres the thing... the ltft goes to 0 right when I give it some throttle and then it correlates directly with my rpms so if I rev up the ltft goes down to 1.00 and then as I let go of throttle the ltft follows and goes back up to 1.20 at base idle rpm. Now I think this has something to do with .e resetting battery and the fact that the o2 sensors read a certain way when in closed loop compared to open loop because they are still learning my driving habits, something to do with how like tuners disable adaptive learning when they tune so they don't have to fight the pcm trying to change settings as the tuner is trying to fidangle with the settings to fix your tune?(I forget what happens but read about this) I'm in closed loop I think from resetting KAM or battery constantly so the adaptive learning hasn't finished drive cycles yet[Or is it open loop, I forget which is which

    I've been fighting a p0171 after JBA Shorty Header install leak that happened to disappear when I went back to stock airbox from a BBK cai so I assumed it was the cai not header anyways now my ltft seems to adapt its value when I step on throttle instantly and goes to 0% when reved up to like 3.5k rpm and then as rpms drop the ltft floats to 1.20[20%] and stays there. Same goes for when a load is applied, depending on how much throttle is applied the ltft goes down to 0% at about 2k rpm cruising throttle. But if I let go or cruise without throttle it goes up to 1.20 again.

    So idk but it kinda seems to make sense that this is a vacuum leak because vacuum decreases when load is applied ? So since accelerating increases load the vacuum needed decreases and then the ltft corrects itself and becomes a function of how much throttle is applied. So at like 3k rpm whether in idle revving or driving the ltft goes to 1.00 anytime iv throttle.

    Now also I just welded in a midmuffler resonator only on drivers side right after h pipe,, but suck at welding so it leaks a little and I threw a p0430 on the side I welded in the muffler right after the h pipe.
     
  5. Juice

    Juice forum member

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    There are Left & right STFTs and LTFTs. Are those mirroring each other or are they different?
     
  6. eighty6gt

    eighty6gt forum member

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    If you don't fix the exhaust leaks you will always have this

    at idle small exhaust/vac leaks cause larger issues. It goes away with throttle because the leaks are hidden by flow
     
    Pentalab likes this.
  7. Mustangk

    Mustangk Junior Member

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    Yes both sides. But the exhaust leaks are post o2 sensors. To my knowledge the shorties aren't leaking if they are ifs very small, and I got the collectors aligned and sealed well.
     
  8. Mustangk

    Mustangk Junior Member

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    Both read 1.20 and the value changes rapidly like stft. I thought ltft was supposed to slowly adapt as the stft adapt instantly as u throttle
     
  9. Mustangk

    Mustangk Junior Member

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    is this normal for open loop ? cuss i reset the battery alot as i tinker with stuff alot it seems
     
  10. Dino Dino Bambino

    Dino Dino Bambino I have a red car

    Age:
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    If you keep disconnecting the battery, the long term fuel trims (LTFTs) won't have enough time to stabilize and will fluctuate almost as much as the short term fuel trims (STFTs). You need to allow the ECU adequate time to log and store the fuel trims. Then they will begin to make more sense.

    Normally they should mirror each other on both cylinder banks (bank 1= passenger side, bank 2 = driver's side). Same goes for O2 sensor voltages (sensor 1 = upstream, sensor 2 = downstream). The four O2 sensors are labelled B1S1, B1S2, B2S1, B2S2 and this will help you differentiate between them when capturing catalogs.
     
  11. Juice

    Juice forum member

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    Ignore the actual trim values. The question is, does the stft swing the same amount in both directions? +20 and -20%?
     
  12. Mustangk

    Mustangk Junior Member

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    why am i ignoring the ltft ? the short terms acts the sameway, it usually will be at around .80 to .85 at idle and then as i throttle it goes to 1.00 at cruising throttle. and so does the ltft goes from 1.20 down to 1.00. so the stft is -20 and the ltft is +20 which i understand as the sensors are working but the sensor values are running too lean and indicative of a vaccuum leak since i throttle and the vacuuum leak goes away at cruising since vacuum load decreases as engine load or throttle increases
     
  13. Mustangk

    Mustangk Junior Member

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    now given that vaccuum load is supposed to decrease as engine load increases because less vaccuum is required when the engine is spinning faster, its hard to realize theres a problem ? im trying to determine how to coorelate engine load value to vacuum or fuel trim to be able to tell if the values are following whatever values they should be at. for example im not sure what engine load should be with 100% throttle or 80% throttle applied and then also what engine vacuum or fuel trim should be at. i assume trim ideally would always stay at 1.00 and never have to trim much, but vacuum on the otherhand should be the opposite of engine load or decrease as load increase
     
  14. Mustangk

    Mustangk Junior Member

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    so I have a stft perfect 1.00 but ltft 1.20 at idle. On throttle 1.20ltft goes to 1.00 and 1.00stft stays around 1.00. Seems wrong because I thought they were supposed to be opposite values or the ltft was dependant upon the short term
     
  15. Mustangk

    Mustangk Junior Member

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    Is fuel pump voltage of 7.00 or hovering Round there 6.98~ correct and healthy. That's for actual voltage at fuel pump I believe it's a data log point from litos configuration file he sent me
     
  16. Juice

    Juice forum member

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    Stricktly looking at the STFT swing from .8-1.20 may actually be ok. After a reset, I can see STFT swing that much on mine. Once LTFT starts to read, STFT swings get much smaller. If the pcm is not throwing a lean code, I would not be concerned.
    P0430 has no affect on fuel trims, it simply means the catalytic converter is wearing out.
     
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