Very good information! Simplicity at its best! I've learned over the years (40 years) that you can always tell how well someone understands a concept or principle by how ell they explain it. If they can't explain it they simply don't understand it. Thanks for sharing!
ok so what is mine doing if my stft is around -3% to maybe +5% but my ltft is consistently +10.9% no matter what the load is? and to help diagnose it my car is an ld9 i4 2.4l dohc engine with around 75k miles on it! ive recently done plugs, coils, coil boots, new battery, and cleared a couple unrelated abs codes so the car would shift smoothly so i could drive it and perform these tests. any info would help quite a bit on trying to find my issue! hopefully its just a small vaccum leak somewhere lol!
Short term fuel trims on both banks increase from about 4 to 30 when I rev. the engine on idle. After letting go they immediately drop back to 4. I would assume this is normal.
I'm not an expert but I would think you might have some fuel delivery issues (weak fuel pump clogged injectors etc)....do you have any drivability or idling issues?
@@macknumber9 We did have a bad fuel pump, but the STFTs normally do what I described 1 year ago. It is the LTFT we needed to look at. Also the pump specified a certain PSI when we hooked up a gauge to the schrader valve. Our pump was way below the specified value and that's how we concluded it was a weak fuel pump.
@OldSchoolNoe yes stft will bounce but it depends on where ltft is. If you mean bouncing is +5% to -5% swings that's exactly what you want. That means the pcm is able to balance the air/fuel mixture with THAT ltft. If STFT is doing this with LTFT at +25% though then that's a lean problem...
Hello, i had negative fuel trims in my car like -18%, los of power and bad idle, i changed the maf the car run very smooth now, and have much more power but Ltft has gone -25%. Any idea why the fuel trims went more nefative but the cur runs better? Could be the ne maf faulty as well??
I have a problem, sometimes my vehicle will have a rough idle, i check it using a cheap obd scanner, i found the short fuel trim drops about -10 , o2 sensor working fine and maf sensor, i also clean the injectors and replace fuel pump
Automatic, balanced and automatic correction auto balance, and auto correction. I think that’s what this whole thing is trying to do automatically. Why don’t we just call it automatic balance control
Very good description of short and long term fuel trims. Man i have a problem, my suzuki areo longterm fuel trim is constantly around 9 while short term is around -1 to +3 . while my petrol average is drops from 12L/km to 6L/km in city drive.
When you observe Short-Term Fuel Trim (STFT) around -1% to -3% and Long-Term Fuel Trim (LTFT) around 9%, it typically indicates the following: 1. **Short-Term Fuel Trim (STFT)**: - STFT values between -1% to -3% suggest that the engine is slightly compensating for a rich air-fuel mixture. Negative STFT values indicate that the engine is reducing fuel delivery to correct for a potentially rich condition. This adjustment is happening in real-time and can vary as driving conditions change. 2. **Long-Term Fuel Trim (LTFT)**: - LTFT around 9% indicates a consistent adjustment made by the ECU over time to compensate for a lean air-fuel mixture. A positive LTFT value suggests that the engine is adding more fuel than usual to achieve the correct air-fuel ratio. This adjustment helps to address persistent lean conditions that might be caused by factors such as aging sensors, minor vacuum leaks, or changes in fuel quality. In summary, with STFT around -1% to -3%, the engine is currently adjusting to slightly reduce fuel delivery due to a perceived richness in the air-fuel mixture at that moment. LTFT around 9% indicates a longer-term adjustment to compensate for a lean condition by adding more fuel over time. These values are within typical ranges and indicate the engine's adaptive capability to maintain efficient combustion.
I'm trying to get my head around fuel trims. Would I be correct that a vacuum leak would cause the engine to run at a higher idle speed than normal? My logic says it would, but I've never heard of a high idle speed being a symptom of a vacuum leak before. Thanks for your help.
My car had a short term fuel trim of plus 5 or 6 and a long term of minus 6 or 7 so i thought it may be due to the air filter and injectors being dirty. I changed the filter and used some injector cleaner now my short term is pretty much zero but the long term is still minus 6, should I do a idle relearn??
@@Capt.Rankin had a small tear in the rubber intake tube going from the air filter box to the throttle body, right in the bend. Didn't notice it until I was changing out my airfilter box because it had a crack around the rim. Got all that fixed then a uninsured driver tboned me, totalling the car.
@@hunterautomotive4842 when I rev and hold it at about 2000rpm the stft goes to about -22.34 and ltft goes to -0.78 At idle stft is at 3 to -3 Ltft is at -10.16
My long term bank 2 is around +9% at idle while short term for same bank keeps trying to slowly subtract fuel (-1 -2%) but it never really tries to add fuel....strange because the computer obviously sees this bank as running lean because it has increased the long term but you would think it would settle in and start oscillating from adding fuel to subtracting fuel because the cat needs both gases....mine just subtracts fuel while running long term +9%
They made cars too complicated. I'm thinking that if the computer and sensors are working properly to maintain the correct AFR, then should I care about a "high" LTFT. Bank 1 is +14% and bank 2 is +12% but the car drives good and there are no codes. STFT alternates between +/-3%. I don't have anything to measure AFR. By the way, I'm not a professional mechanic that has access to all the "toys" (test equipment). But I would like to get the LTFT under 5% and hopefully without breaking the bank.
Hello. 2003 Mitsubishi 3.8L V-6, 220,000 trouble free miles. Fuel economy is where it should be. LTFT 1&2 are +12.5% at hot idle. But goes to 0% and stays there when revved to 2,500 rpm. STFT 1&2 are 0% at hot idle. When extra fuel is sprayed on identified leak of intake manifold (leaking o-ring, I used smoke to find) the STFT immediately goes to -6 and then returns when the extra fuel is burned off. Could this intake air leak thats affecting both banks cause the truck to go into a limp mode, giving me these codes? P0335 P2135 P0340 Also, why does LTFT go to 0% when under load? Thanks!
air leak most certainly can make your car go into limp mode (though i assume you already fixed the problem since it has been 1 year) and air leak will add more air then the car is expecting if it is behind the maf, resulting in high o2 in exhaust, the o2 sensor will tell the car this and the injectors will pump in more fuel, the car will notice that it is pumping in much more fuel then the maf wants and will probably set a fault code in the maf
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Wow , BEST EVER simple explanation. And total of 4 minutes ! This is by far the best with out far to much talk…… thank you
This is a perfect simple explanation of both the stft and ltft and how they can be used, thank you.
This 4 minute video explains everything. Thank you sir.
Very good information! Simplicity at its best! I've learned over the years (40 years) that you can always tell how well someone understands a concept or principle by how ell they explain it. If they can't explain it they simply don't understand it. Thanks for sharing!
Very well said. Simple, and you explained it well without him'n and haw'n. Thanks.
Great video, super easy to understand opposed to some internet guides
Excellent understandable description.. thanks!
very well done thank you! awesome.
really good explanation thanks
Thanks so much. Excellent explanation.
Appreciate the info. Mine are off as a symptom of a misfire I cannot FREAKIN FIND!!! Gah. Thanks!
Need a forum or group where can discuss diagnosis of OBDII data.
Thank u
I see you don’t make videos no more. Just wanted to thank you for this information.
Just wondering what would happen if my short-term fuel trim kept going 5, -3, 8, -7, the only time everything zeros out is when I floor it
ok so what is mine doing if my stft is around -3% to maybe +5% but my ltft is consistently +10.9% no matter what the load is? and to help diagnose it my car is an ld9 i4 2.4l dohc engine with around 75k miles on it! ive recently done plugs, coils, coil boots, new battery, and cleared a couple unrelated abs codes so the car would shift smoothly so i could drive it and perform these tests. any info would help quite a bit on trying to find my issue! hopefully its just a small vaccum leak somewhere lol!
Thank you very much,quick and easy .Great video.
🤝
How much is this sensor?
Great video, very helpful, thanks
I have high short term and low longterm. +30 short and -19 longterm. What does it mean?
Great Vid...What if My Long FT stay at 24.2 fast or slow driving ??? #07chevytahoe 5.3
Short term fuel trims on both banks increase from about 4 to 30 when I rev. the engine on idle. After letting go they immediately drop back to 4. I would assume this is normal.
I'm not an expert but I would think you might have some fuel delivery issues (weak fuel pump clogged injectors etc)....do you have any drivability or idling issues?
@@macknumber9 We did have a bad fuel pump, but the STFTs normally do what I described 1 year ago. It is the LTFT we needed to look at. Also the pump specified a certain PSI when we hooked up a gauge to the schrader valve. Our pump was way below the specified value and that's how we concluded it was a weak fuel pump.
@@OldSchoolNoe what do you mean the short trims normally do what you described?
@@macknumber9 STFTs bounce around as you step and release the pedal
@OldSchoolNoe yes stft will bounce but it depends on where ltft is. If you mean bouncing is +5% to -5% swings that's exactly what you want. That means the pcm is able to balance the air/fuel mixture with THAT ltft. If STFT is doing this with LTFT at +25% though then that's a lean problem...
Hello, i had negative fuel trims in my car like -18%, los of power and bad idle, i changed the maf the car run very smooth now, and have much more power but Ltft has gone -25%. Any idea why the fuel trims went more nefative but the cur runs better? Could be the ne maf faulty as well??
It's been 2 years, were you able to figure out what was wrong?
At what point do you reset LT fuel trim? Gasket change, found a vac leak and fixed it?
No need to reset it. If you fixed the problem LT will fix itself.
I have a problem, sometimes my vehicle will have a rough idle, i check it using a cheap obd scanner, i found the short fuel trim drops about -10 , o2 sensor working fine and maf sensor, i also clean the injectors and replace fuel pump
Possible fuel pressure regulator stuck closed
Automatic, balanced and automatic correction auto balance, and auto correction. I think that’s what this whole thing is trying to do automatically. Why don’t we just call it automatic balance control
Good stuff, how about very high short trims, 25, and mid long, around 9 or so?
I have a p0430 code and I'm getting a flat reading on both long term fuel trim what do this mean?
Found a solution?
Very good description of short and long term fuel trims.
Man i have a problem, my suzuki areo longterm fuel trim is constantly around 9 while short term is around -1 to +3 . while my petrol average is drops from 12L/km to 6L/km in city drive.
When you observe Short-Term Fuel Trim (STFT) around -1% to -3% and Long-Term Fuel Trim (LTFT) around 9%, it typically indicates the following:
1. **Short-Term Fuel Trim (STFT)**:
- STFT values between -1% to -3% suggest that the engine is slightly compensating for a rich air-fuel mixture. Negative STFT values indicate that the engine is reducing fuel delivery to correct for a potentially rich condition. This adjustment is happening in real-time and can vary as driving conditions change.
2. **Long-Term Fuel Trim (LTFT)**:
- LTFT around 9% indicates a consistent adjustment made by the ECU over time to compensate for a lean air-fuel mixture. A positive LTFT value suggests that the engine is adding more fuel than usual to achieve the correct air-fuel ratio. This adjustment helps to address persistent lean conditions that might be caused by factors such as aging sensors, minor vacuum leaks, or changes in fuel quality.
In summary, with STFT around -1% to -3%, the engine is currently adjusting to slightly reduce fuel delivery due to a perceived richness in the air-fuel mixture at that moment. LTFT around 9% indicates a longer-term adjustment to compensate for a lean condition by adding more fuel over time. These values are within typical ranges and indicate the engine's adaptive capability to maintain efficient combustion.
What if my short trim is at normal range most of the time 0%, but long term is always high around 20%. Been having this problem for a while
Vacuum leak. Most likely
My short term fuel trim is at 20% but then goes down to 11% and my long term goes from 3 to 1% 😭😭
I'm trying to get my head around fuel trims. Would I be correct that a vacuum leak would cause the engine to run at a higher idle speed than normal? My logic says it would, but I've never heard of a high idle speed being a symptom of a vacuum leak before. Thanks for your help.
it is on older carbed cars. If it's bad enough, it may not even start or will start but "idle" at 2.5-3k rpm
easy well explained
My car had a short term fuel trim of plus 5 or 6 and a long term of minus 6 or 7 so i thought it may be due to the air filter and injectors being dirty. I changed the filter and used some injector cleaner now my short term is pretty much zero but the long term is still minus 6, should I do a idle relearn??
Did you ever figure out what it was?
@@Capt.Rankin had a small tear in the rubber intake tube going from the air filter box to the throttle body, right in the bend. Didn't notice it until I was changing out my airfilter box because it had a crack around the rim. Got all that fixed then a uninsured driver tboned me, totalling the car.
@@donniev8181 it be like that
Fuel trims supposed to be under 10%? My long term reads 11- 12%
Engine is running rich, injectors leaking, fuel reg is stuck closed, MAF sensor failing
When I rev my rpm to a higher idle my stft goes way negative pass -10 what could it be
Remember O2 sensors drive the stft numbers. So what are the O2 sensors saying at the same time?
@@hunterautomotive4842 when I rev and hold it at about 2000rpm the stft goes to about -22.34 and ltft goes to -0.78
At idle stft is at 3 to -3
Ltft is at -10.16
My long term bank 2 is around +9% at idle while short term for same bank keeps trying to slowly subtract fuel (-1 -2%) but it never really tries to add fuel....strange because the computer obviously sees this bank as running lean because it has increased the long term but you would think it would settle in and start oscillating from adding fuel to subtracting fuel because the cat needs both gases....mine just subtracts fuel while running long term +9%
They made cars too complicated. I'm thinking that if the computer and sensors are working properly to maintain the correct AFR, then should I care about a "high" LTFT. Bank 1 is +14% and bank 2 is +12% but the car drives good and there are no codes. STFT alternates between +/-3%. I don't have anything to measure AFR. By the way, I'm not a professional mechanic that has access to all the "toys" (test equipment). But I would like to get the LTFT under 5% and hopefully without breaking the bank.
Money bro!
Short and Long Term Fuel Trims tell you something is not running normal but not even a hint what the problem is. mostly it could be this and that
Hello. 2003 Mitsubishi 3.8L V-6, 220,000 trouble free miles. Fuel economy is where it should be.
LTFT 1&2 are +12.5% at hot idle. But goes to 0% and stays there when revved to 2,500 rpm.
STFT 1&2 are 0% at hot idle. When extra fuel is sprayed on identified leak of intake manifold (leaking o-ring, I used smoke to find) the STFT immediately goes to -6 and then returns when the extra fuel is burned off.
Could this intake air leak thats affecting both banks cause the truck to go into a limp mode, giving me these codes?
P0335
P2135
P0340
Also, why does LTFT go to 0% when under load? Thanks!
air leak most certainly can make your car go into limp mode (though i assume you already fixed the problem since it has been 1 year)
and air leak will add more air then the car is expecting if it is behind the maf, resulting in high o2 in exhaust, the o2 sensor will tell the car this and the injectors will pump in more fuel, the car will notice that it is pumping in much more fuel then the maf wants and will probably set a fault code in the maf
@justarandomguy3969 I never figured it out actually. It just went away.