Understanding the basics about fuel trims 

After many many videos I have watched on fuel trims I never thought someone will come with a new approach. I think using the rc car is the best example I have ever seen on fuel trim. Well done. 👍

I just found out that fuel pump pressure has a big influence on short trim and fuel trim correction. The lesson you gave really helped me understand this. Thank you

Extremely well presented. This video answers a multitude of questions concerning fuel trims. Using generic data to view fuel trims is not included in any diagnostic scanner's instructions. I have been plagued with trying to read fuel trims on Nissans for some time now. Thank you!👍

That was an awesome demonstration of fuel trims. Thank you.

I liked the injector on time portion showing the computer adjusting. o2 sensor response is very critical too. Meaning a lazy o2 signal or o2 heater circuit. 👍👍

Generic OBD2 gets overlooked by a lot of guys especially once they get their hands on higher end scan tools and wind up getting themselves in trouble chasing substituted values. I use Generic OBD 2 a lot when chasing issues such as fuel trim.

It's important to understand that the short term adjustment is always added/subtracted to/from the long term, to get the correct 'instantaneous' fuel/air balance, as seen by the O2 sensor...

I wonder which institution you teach at. Without formal training I have tried to understand fuel trim through others but not everyone is possessed with the gift of imparting knowledge. You possess that ability and does so with ease. You can only explain something if you truly understand how is operates and you do. This have brought me to a better place and a better understanding of how fuel trim works. Thanks man keep up the good work. 👏

a decade looking for avideo like this. just can't thank you enough.

A very excellent explanation and we have benefited from the basics and we are waiting for more information.. I have subscribed to the channel and activate the bell to receive more. Thank you very much😇

Thank you for taking the time to make the video. This is really helped me gain a much better understanding on the subject.

Thank you so much! You have explained Fuel Trim, this is an Incredible Golden Nugget of Knowledge!

The best "show and tell" tutorial on fuel trim I have seen, you definitely do not have to be an engineer to understand this. Thank you for taking out time to help on this.

Dynamic and useful explanation Thank you

I'm going to use my old RC car to teach this to my apprentice. Great demonstration here

Thank you. Finally i understood LTFT. Fuel trims are important also for unmetered air issues.

You are the best of the best. I hope that most of the "auto mechanics"here in California start watching your videos so they can learn something about fuel trims

I loved the practical demonstration! Thank you.

How to verify that your o2 sensors are actually reporting correct info? That's extremely vital

This was definitely the best fuel trim video I have ever seen. I am having a problem with a P0401 code and fuel trims around -12 to -16. Very informative!

This kind sir was really informative I'm here in Jamaica and I have a 2007 Suzuki Grand Vitara that's running rich in bank 2 @ -22 . I'll be looking into that injectors tomorrow thank much

So complicated.

Great video, thank you sir 👍

Nice explanation! I easily understand that the computer expects a certain fuel pressure and has a map of the expected injector pulse width for the flow of air into the engine, and corrects based on what’s being actually measured.

Awesome video I got a Foxwell NT809BT Scanner it's all setup just need more deeper understanding how to find faults Great video about fuel trim thanks

Finally, understand fuel trimming. thx

I already know about the theory. But the practical part is fantastic. Many thanks.

Thank you very much for this Excellent explanation!!!

excellent video. The CAR controls really helps. In my case, it seemed I had to keep clearing out codes/pending codes until the LTFT came into compliance - after a badly leaking exhaust. I seem to be on the good path now! Cheers.

I put four new Denso fuel injectors in my Civic with the R18a, and although it runs well, the fuel trims went from negative 5-8%, to positive 4-6%. Does this tell me my new injectors are undersized?

Have been very much interested in understanding fuel trims and after watching this I can now say I've got the point I've been missing thanks. This is my first time in this channel and i like it.

2007 Toyota sequoia. 4.7L v8 . Lean code p0174 bank 2 . Fuel trim are : B1 , short trim 1.6 long trim 11.7 B2 , short trim 1.3 long trim 22.6 What is going on ?! Please, your professional opinion matters. The code is gone after deleting it and didn’t come back yet . The trims are worrying me . Thank you so much .

Not a popular way of framing it, perhaps, but an aircraft is indeed a vehicle. 😂😂😂😂😂😂

Yes Fuel Trim is Very Complicated to understand but with the Hands-On example how about ' Controlling a Model Car You put Light in ~ a Dark Tunnel dude! 😮👏

If you can rely on the fuel trims everything is pretty simple, but I have a problem here where the fuel trim values ​​are good, but only when the air conditioning is on. If I turn the air conditioning off, the values ​​deteriorate drastically, over 10 and more in the short term and then finally also in the long term, to the point that it sets a P0130 (bank1 sensor 1 electrically faulty) code and often also a P0171 (system too lean). Why do the values ​​deteriorate so much when the air conditioning is off, doesn't make sense to me? Does anyone have any ideas about this? This way it won't pass the emissions test.

Hello sir . Great video . I’m starting watching your videos . Question do we need to add the 2 banks to see results or just both trim at 1 bank ? I’m sorry I didn’t get that part. Thank you sir .

My car volvo, s40 2003 always hunts around 0-% short and 13.5/15.00% + long term. Cant work out what the heck is going on!

I’m new to the mechanics world of engines. I now do have a much better understanding of how Trims work. My question is, how can we use the information that we see on an OBD scanner on trims to help us fine-tune performance? Or diagnose issues. Cheers from Canada

Finally, a video that open my mind on what I have considered a very hard subject to understand .

Very informative, bro. It's greatly appreciated

In a nutshell shell, short term fuel trim is instant fuel data and long term is just that….average fuel trim data over time.. Much like instant MPG or average MPG …..

Hi, my car engine is on for code : evaporative system- long term fuel trim. My question is it safe to drive 45 mins to mechanic to fix ? Is it very dangerous on the road? Please advise? Thanks!

Very very good video. simple and understandable. thanks.

Good morning, please short term positive 20 percent and long term negative 28 percent, please the meaning

Wow best explanation for a beginning mechanic!

Curious if you can answer this one? Supercharged car. The car is speed density (MAP sensor- no MAF) and tuned in summer time. Would winter weather show positive fuel trims?

Great way of explaining this, the steering alignment analogy is very intuitive 👍

Thanks for the Video its So Easy Now i Got it 100% 👍🏼

Very well done vid !!!

Good stuff! Thanks for posting!!

Thank you so much. I’m not a pro, but I’ve made it a goal of mine to understand fuel trims. I’m a pilot, and your airplane trim analogy did the trick. I have a low level scan tool that I’m trying to understand for my car and at least now I can get the high level overview that previously escaped me. It’s a 11 yr old 3.6 GM with 160,000 miles that seems to run quite well, but as they say knowledge is power. I subbed.

Very well put together. I finally get it , Ty

Great explanation!

I really enjoyed this very cool and simple explanation about fuel trims. Wish you had explained that to me 27 years ago! Have a wonderful New Year 2022 with family and friends. Same for all other commentators.

Your very good teacher thank you 👍

Definitely the best video on this topic on RU-vid. Going to add this to my playlist. Thank you.

Great representation of fuel trims! Love the RC car and the live car example! As always great content!

Excellent teaching love it and tank you

I want one of those remote control cars

Excellent l really like the live demonstration.

2015 supercharged mustang 5.0. Fuel trims at idle and warmed up. LT and ST. Around 0. Driving 2000 rpm ish. Bank1. -12. Bank2 -2. LTFT. Any ideas. I/M monitor Fuel will not set. Any input?

Thank you so much brother for putting this in easy to understand terms...Ive always heard of the fuel trims but its something that remained esoteric to me, never understood it b4.... Eager to take a fresh look a a car thats had much trouble during startup ,observing the trims... In an OBD1 system, is there any way to get this info? I also have an older car , a 94 thats definitely running too rich ..this kind of info would be invaluable but how to retrieve it on an older obd1 system? thanks!

Thank you !

is it only for petrol engine or for diesel too? Thanks

Best video out there on fuel trims! If someone can't understand this, then they are just not capable of understanding anything

So what causes an engine to run rich? I have LTFT in park for B1 & B2 at -14 to -18%. With STFT B1 & B2 at 0 to 4%

Brilliant well explaind 👍

I learned lambda is measuring oxygen so I got it wrong. Fuel trim is fuel. I've been confused for a long time. OK 👌

😃wow, I just came across your stellar teaching on this topic of fuel trims! Bravo! Short & Long adding together and understanding how fuel pressure can impact the duty cycle of the injectors as well as all the trim. This is helping me take over the troubleshooting of a lean condition on a Cadillac engine with codes 171 and 174 (lean on banks one and two). I'm looking at fuel pressure tomorrow and your excellent teaching has put me on a path that I think i can solve it. Thank you sir. -jeff

This video was excellent!

Am having a negative long term fuel trim of about (-7) and short term trim of about negative (-3) consistently. What's the issue please? It's an Acura TSX 2006 Auto.

I have had high long term fuel trims for months on my 2007 Ram 1500 5.7L. They are both at +15.6. Using a smoke machine today, I found a leak where the EGR valve attaches to the tube that goes to the exhaust. I thought for sure I had found the problem, but after replacing the EGR and resetting the ECU, the problem is still there. In fact, immediately after starting the engine after resetting the computer, the long term trims went straight back to +15.6 instantly even though the short term trims stayed right around 0. The o2 sensors are functioning fine, however they are old. I have put 70,000 miles on the truck since I bought it, and it has 193,476 miles on it. I have not replaced the the o2's since I have owned the truck. When I rev the engine to 2000 rpm, the long term trims go to zero and then go back to 15.6 when I go back to idle. Anyways, something doesn't look right.

thanks verry much i learn a lot

Very helpful video! My car yesterday on idle reached -45 Short term and +16 Long term. With the rpms at 2000 both was 18-19. What would that be?

Your videos are great and I want to learn. Im having a hard time navigating utube. Where do I go to get more information on the courses that you offer, there must be a website?

Hi I’m going crazy with my 2003 Mercedes’ c180k. The emissions are extremely high on the CO and the lamda is running rich. I found a split hose under the supercharger and replaced it. I also had a slight seepage on the fuel regulator and replaced that too. But still the car is running extremely rich. If I disconnect any one of the injectors then the CO level comes right down to almost zero. But with all 4 running it’s too rich. Please can anyone advise. So far I just have a code of P2058 which is lamda upstream. But on a scanner it shows to be working as I see the voltage fluctuating slightly. Please can you help?

you kept saying add the long and short to get a total then whats the point of having a long and a short if total is what matters, i would think the most basic of basics is to know why there is a short and a long instead of just a total???

Perfect, perfect, perfect...👋👋👋

What about 14.7 to 1 parts air to fuel? You the computer is playing the game for 0

Best video, best information, I've found so far regarding fuel trims. Nice and clear. I especially like how Mr HoAT set up a system to reduce fuel pressure to the injectors, showed us a gauge that was indicating the pressure and the changes in pressure, and showed us how the OBD trim values changed in response to the changes in fuel pressure - changed in order to keep the vehicle at "homeostasis" as they call it in biological feedback systems. I loved the info about the etymological origin of the word "trim" - starting with how the word is used, what it means, in the context of sailing vessels. Only thing I had some difficulty understanding was the fuel injector oscillograph pattern starting at 21:20. I think the problem here was that I was not able to see the labels for the vertical and horizontal axes. The labels were too small to see. I saw what looked like 2-digit numbers on the vertical axis that were too blurry to actually read, and in addition I saw just the numbers, I did not see any label saying what the numbers were a measurement of. Whatever was on the horizontal axis was even harder for me to see. Is it time, in milliseconds, on the horizontal scale? At what frequency was the oscilloscope re-drawing the screen? What was on the vertical scale, volts? Why was an increase in injector on-time associated with a flat, horizontal line at the _bottom_ of the vertical scale (a line which got longer as the fuel trim went more positive)?

Basic control theory. Many systems in the modern car are using a PID control loop to maintain some kind of stasis, e.g., fuel ratio, cruise speed....etc. Some of the most fun projects I ever worked on were based on this.

Hi i just subscribed. Thanks for sharing your video. I just have a question. I wonder where did you connect the OBD scanner to the port? Usually the ports is inside the car underneath the steering wheel.

THIS VIDEO IS A MUST WATCH WATCH 10 TIMES. MAYBE 11. AWESOME DUDE.

Good morning ,Hands-on AutoTraining Brian Mann Outstanding tutorial 👌 My mentor SHREWD, QUICK-WITTED, SHARP Hands on Auto Training Brian Mann 👍 From Nick Ayivor from London England UK 🇬🇧 ⏰️ 07:12AM

So what's on your video again more? Understanding it better before I wrote what I wrote I know I have a slight feel pressure that is the little bit lower than normal and that's why my long-term field trim is pretty high and when I rib app the gas for short-term field trim it goes down I'll see if I can replace my fuel pressure my I guess my philip later on tonight

Thanks Much! Explained WELL in layman’s terms.

Great video, why was the fuel trim at +7 before you reduced the fuel pressure?

Very good explanation for this old school mechanic starting out working on my own vehicles again. My son tried explaining it to me but you explained it better. Thanks

Thank you very much for your well explanation. Now I have a better understanding of fuel trim than before.

Goodday Profesor. Can you please explain difference between oxygen sensor and air fuel sensor, thankyou

Thank you very mach.

WOW FINALLY SOME ONE EXPLAIN EXACLLY WHAT THESE NUMBERS ARE DOING AND WHAT IT MEANS. THAMK YOU SIR......

Do fuel trims % value effect all fuel table, and at WOT ecu use the % its detected at idle, do I understand right?

Very repetitive , do assume it uses 2 lambda sensor for closed loop short and long term

I'm a diyer. so working on a 2008 honda civic 1.8 liter. I have negative fuel trims all of the time. at idle, my STFT and LTFT, always on the negative side. even while I'm driving the car between 1500 rpm and 1800 rpm. what am I missing? How should I tackle this issue. thanks.

My ford focus has 99% on the bank 2 Long term fuel trim.. And I can tell the car is not responsive, especially if going up the hills. Is it actually possible that the car can still go on with that amount? Or is it something wrong with just the sensor and that causes the car to be unresponsive?

That was awesome and very informative

thank you for simplifying fuel trim, i have a snowmobile turbo boondocker setup with 5psi of boost when purchased. Turbo blew, i brought sled to Mod shop that does sled mods but they could only get 14psi as new low . So now i have to purchase av gas too keep the sled cooler, like the power but its not my liking. id like to put back to stock if i can. Would i be able to just unplug the boondocker fuel mapping box from the efi carbs and plug in the original back in to get stock settings. i will also be putting original exhaust back on also and remove turbo.

Thank you for sharing your knowledge and experience!!!

BEING IN THE TRANSPORTATION REPAIR FIELD FOR 50 YEARS NOW AM STARTING TO UNDERSTAND FUEL TRIM PLUS THE REASON WHY THE READING ARE POS-NEG.AII THIS I KNEW I HAVE THE UNDERSTANDING,I FEEL IT THE PERSON WHO TEACHING IF YOU CANNOT GET THAT TECH TO SEE ARE UNDERSTAND WHAT YOU TRYING TO SAY. YOU ARE WASTING HIS TIME& YOUR, PLEASE KEEP-UP THE GREAT WORK, [ DADDYDAVE 707 ]