Understanding+Diagnosis: Adaptive Fuel Learn Strategy

For Expert DIY's only!! High level material on exactly how the PCM uses the "learned" Long Term Fuel Trim to adapt to variable conditions. This material is helpful in knowing how to properly use and analyze fuel trim data from your scantool, understand why you sometimes seem to get unexplained variability in fuel trim analysis, and quite honestly: it just makes you a true car geek.
Disclaimer: This level of material is honestly as far as I really go for my "hobby" so it somewhat stretches my limits. The material is not intended to be 100% accurate but more to give the necessary understanding of the concepts enough to help you make good diagnostic decisions in your data collection and analysis.
It is essential to understand Fuel Trims very thoroughly to comprehend this video. My Fuel Trims primer is here:
• Secret of Engine Probl...
The Jeep lean condition video referred to in this video is here:
• P0171, P0174, Misfire ...
I hope you enjoy it!

[@williamst.pierre7753]

Don't underestimate your audiences thirst for knowledge, you are doing us a great service and we appreciate what you have to offer, thanks!

[@SchrodingersBox]

I appreciate that! Yes you are right, I severely underestimated and will keep that in mind for sure next time!!

[@Ali_Alhamaly]

27:30

[@bigmike2149]

Agree 💯

[@kaseemamere1626]

👍

[@83bebo1]

Perfect as usual. Whatever the lenght of your videos, the 2% are all ears

[@juanitotucupei]

Dang, this is like the last element to your “secret of engine diagnosis” video. The fact that then we rev up we are pulling the Pre-established learned fuel trims on the fuel strategy, and not necessarily the “live” data per say. Learned so much more again. THANK YOU.

[@observersnt]

Hello Matt. I am a sixty year old former marine engine fitter living in the north east of a small island off the west coast of Europe called England where four cylinder engines are rather NORMAL and any more than four is abnormal!! I have repaired and serviced first, my own and subsequently my family’s cars for decades. My first rebuild was a FOUR !!! cylinder 1100cc engine I n 1968. I grew up on and revered Weber twin choke carburetors with their numerous options of chokes and jets. I am of the old school mentality but now, decades later, I am staring into the abyss of engine management systems and diagnostics. Admittedly we now have reliable, efficient comfortable cars with performance that would have been breath-taking in the 1960’s and 70’s and we are spared many of the frequent frustrations that afflicted us. The need to get to grips with engine management and its diagnosis is critical. Just like air moved faster than fuel through the venturi of a carburetor and caused a weak spot until the fuel caught up or an enrichment device opened up, technology became the equivalent of the air and our knowledge, like fuel lagged behind. Now thanks not only to the availability of diagnostic equipment but also to the likes of, Schrodinger’s Box, Scanner Danner and Eric the Car Guy etc. the public and professionals alike are eventually becoming more informed, less intimidated and aware of the real value of engine management and how to deal with its “manifold” issues. I am profoundly impressed by the generosity of spirit of those, like you, who have given so much time to share with the world what they have learned themselves, but am a little embarrassed that almost all of the amazing things I am learning are thanks to Americans and that there doesn’t appear to be any similar quality and quantity from my countrymen who one time prided themselves on their engineering prowess. That said, I think that thousands of people the world over will look back and thank you for what they have learned from you. Who can tell what the full extent of your sharing will have, now and in the future, even in remote, small, four cylinder cultures. Having seen quite a few of yours and Paul Danner’s videos, I am now feel that diagnostics is much less intimidating than I previously did, so much so that I went out and bought some PC based diagnostic software and can’t seem to put it away. It goes on almost every journey and already I find I need a much more capable one. Tonight’s viewing was your Adaptive Learn Fuel Strategy. Pausing the video repeatedly allows me to make notes, six pages tonight. I don’t pretend to have understood all I saw, but it was far from the “serious students” palate that you suggested. It really did help me to understand L & STFT better than I did after watching the videos on fuel trims. It was fascinating and while it might seem weird or sad to some, I find these videos technically exciting. At last I am able to grasp terms and principles that until three weeks ago were merely terms or at best vaguely understood ideas and more importantly I am now learning for the first time how to apply what I am learning. A person needs to be working on cars day in day out to acquire real diagnostic skills, but at least now I stand a good chance of correct diagnosis, even if it takes a comparatively long time to arrive at a conclusion. I have a question about mapping that I will withhold until I have watched the video again in case It proves that it would be better to keep my mouth shut and let people think I am an idiot, rather than open it and prove them right. Thank you very much indeed for the considerable effort and time you devote to the videos. Thanks also for the generosity of spirit to share. Tom

[@SchrodingersBox]

+andy scott Thanks Tom- read the entire comment. I usually hear from the crowd that identifies with your demographic that computerized engine management is "poppycock" and they avoid learning new material like the plague. It is refreshing to see some people in the older crowd embrace and try to understand the new technology which is without question better than ever in history by far. Also glad to be included in that list of great names!!! Enjoy the site and thanks for the great feedback.

[@bradybell6129]

WRT his denigration of four cylinder engines, I was going to suggest reminding him of the history of the Offenhauser engine at the Indianapolis Five Hundred until I remembered that you Brits think Yanks are crazy for racing around in a big oval. :=)

[@bandiit420]

I love your videos because I actually come away with new knowledge every time I watch one. You have a way of boiling down complex processes into simple bite size pieces easy to digest.

[@roadboy229]

This is a old video with great information, this guy really know his shit 💯

[@alexandercahoulan6583]

this guy does a WAY better job explaining everything, including fuel trim, than Scanner Danner does. I know I know its sacrilege. Ive learned SO MUCH watching this channel. It just gloriously clicks.

[@SchrodingersBox]

I appreciate that and of course that is a huge compliment. Paul is a friend of mine and I will say we are different in that Paul caters to professionals and students- people with automotive training background. So the level is a step up since they are not new to this material. I focus more on the DIY level so I assume people had no training. He is a fantastic instructor but we cater to different markets. If I was to teach a class at a tech school I imagine people would say “damn dude step it up brah” lol.

[@alexandercahoulan6583]

@@SchrodingersBox haha good point. Its a level up. Hard truth lol I have to mention I just watched your "voltage drop" video. It was enlightening. The overarching point that flow has to be going through a circuit to truly test voltage drop is a key fundamental which I have not considered. Your videos are really teaching me a lot on a subject that was intimidating in the past. Thank you dear sir..

[@alexandercahoulan6583]

@@SchrodingersBox Hey matt I messaged you a week ago. My name is Casey btw. I finally got to see my fuel trims with scanner. No codes or CEL. At idle LT on both banks (v6 accord) is at +7%. ST at idle on both banks is at +14%. Then as I increase RPM the ST decreases to about +7% on both banks. LT stays same. It never seemed to change through driving and idling. One O2 sensor is acting normal (.1 to .7 osc.) and one is not oscillating as much as it should. It stays around .5 but oscillates slightly. All other pertinent sensors read normal. From what I have learned since it is same on both banks, vacuum leak is most obvious theory. Just wondering what you think.

[@alexandercahoulan6583]

@@SchrodingersBox Sorry for longish message. Just I highly respect your opinion.

[@robmut1357]

Excellent video! I picture the fuel map in my head like a big Rubik's cube. This video fits right in with programming my motorcycle's Power Commander. It sits between the ECU and the injectors to allow custom mapping. Pretty cool.

[@ericacherney3132]

I'm a retired heavy duty mechanic with 35 years on the railway.Your lessons videos have really opened up my understanding of today's vehicles allowing me to have fun in my garage.Thanks

[@TheEgg185]

You're a good explainer. Most people go too fast. I understood everything and I don't have very high intelligence. I thought this was VERY important to know and went along with the fuel trim videos I just watched.

[@SchrodingersBox]

Sounds like you have high intelligence to me; one can tell just by how you communicate.

[@kppatel5967]

Very well explained what you wouldn’t think when dealing with real time problem. You opened up another level of understanding and I appreciate the knowledge you have passed on.Thanks once again.

[@bobsack8336]

Dude, thank you so much!! I am an auto tech student currently entering the 4th and final semester. Your videos are amazingly helpful in understanding fuel trim and it's importance. All the best:)

[@AutoDiagnosticsPK]

27:27 Matt, its more than 9 years and we are still hanging with this video 😂 Don't worry keep going with the great stuff

[@SchrodingersBox]

glad to hear hahaha. so far it’s still very relevant.

[@LOCOTouareg]

honestly... the best ever channel i came across with, thank you very much for all videos

[@user-we5mi6zl2s]

I am understanding and repeatedly watching your videos. It's very interesting and well presented. Thank you Matt.

[@SchrodingersBox]

Great to hear!

[@marynunn1708]

Very informative. Thanks so much. Great to now know how the LTFT, STFT and lookup tables all interact and to learn they’re stacked. Wow. Just got through diagnosing a P0171 lean code that showed up immediately after swapping the turbo on my ‘13 Chevy Cruze 1.4L 4 banger. Used propane while watching both LTFT and STFT and found the air leaking in around the PCV-to-intake fitting. Replaced O-ring and viola’, everything back to normal in just minutes. Now, when the fuel pump gets lazy, I’ll know how to tell difference between low fuel pressure and a vacuum leak. Smart whiteboard!

[@wjohnsonism]

Makes sense to me. Great job. Just started using a scan tool for a BMW and have had high LTFT numbers. I was thinking that they were real time, but the "adaptive cell" and learning concept was like a light bulb going off. Thanks.

[@labradormcgraw]

This video is the perfect complement to the 'Understanding Fuel Trims' tutorial. I must admit that I had to watch it a few times in order to get it pegged, but it really does have its benefits once you understand it. I think the main take-away here is understanding the relationship between dynamic data (stft) and stored data (ltft). Whilst learning about the grid system has no real advantage in the field, it can facilitate those tricky analyses that demand deeper investigation. For the die-hard DIYer, this video is essential viewing.

[@LeakyDiaper]

Beautiful, made perfect sense. Just witnessed all of this a few days ago with a 01 Nissan Quest I was working on. Explains everything I was seing. Turns out it was a leaking fuel pressure regulator and a leaking fuel injector.

[@edwaggonersr.7446]

Having made a good number of multilevel spreadsheets it is easy for me to understand the concept. Now, applying the concept to real world problems that is a different matter. I think anybody who has watched the other "fuel trim videos" should absolutely watch this one. It might even be good to watch it first. Fantastic.

[@RamzyAAF]

Well done Sir. I finally understand the need for and use of LTFT; without knowing the concept of the map the idea of having both STFT and LTFT seemed redundant and caused me to doubt my understanding of them - but now it's clear. Thanks.

[@Ilovetosingem]

Hi Matt So glad you did a recap at the begining as it helped to confirm some points. Thanks a lot and all the very best.

[@MrJcardimen]

Great stuff! I've never heard these concepts articulated so succinctly and clearly. It really broadened my knowledge. As always, you put the cookies on a higher shelf. It's good for us to have to reach a little. Keep up the excellent work.

[@DENicholsAutoBravado]

Jeffrey Cardimen When I'm here, I get top shelf cookies? So cool! :)

[@maqbooljamalivlogs7727]

Best video i ever seen about feul map adaptation

[@stuart1030]

Such valuable information, i enjoyed every minute. THANK YOU. You are a natural teacher that speaks a learner's language.

[@SchrodingersBox]

Thanks for the nice compliment!!

[@ozzstars_cars]

Good explanation on the "behind the scenes" of fuel trim percentages. Good info for any car geek like myself

[@georgeskomorowski]

way-to-go-buddy....You did your home work!!! Thank you sooooo much!! You were not talking to yourself...

[@jeremyhiatt573]

Nice work Matt!! Always wondered what the pcms fuel maps were. New they were important, but didn't know how. I can visualize them now and see the role they play. You may feel like your loosing us, but I think it is just your repitition of the main points, it helps a lot with retention. Anyway, thank you again for your knowledge

[@carlthome6004]

Excellent explanation. Thanks for sharing your knowledge.

[@kevinstory6552]

For what it is worth i thought you did a very good job explaining a very complex and mind boggling subject and knocked it out of the park. And yes i did watch to the end understood some of it before but completely understand it all now and i quit wrenching 25 years ago. I did go to school for diag but wow, keep it up , u inspired me to rethink it.

[@SchrodingersBox]

thanks man!! what a compliment!

[@CesarGarcia-ft7wu]

april 20 2016......just thank you.. for giving us all this info...GOD bless you.

[@davidhobbs1691]

Good info and your presentation skills are always spot on!

[@jennaj198]

Great videos. Learning alot watching your videos DIY Tutorials. I have a Innova 3140d OBD1&2 DTC. And trying to diagnose codes from internet searches has been leaving me with alot more optional multiple choice repair decisions and costing more money. Currently have the O2 sensor STFR & LTFR decisions.

[@Ali_Alhamaly]

Great example @ 18:40 really helps in clarifying the need to look at both long term and short term and what to conclude from them

[@user-qn5yt8fx9i]

One of the best videos in the Channel

[@deldrimor]

Great video. Really helped to re-enforce those fuel trim concepts. Itching for a chance to put some of these concepts into practice. Thanks!

[@SchrodingersBox]

deldrimor Good for you!! I can count maybe... oh, 2 times ever that this info came in handy (one was in my last video actually lol) but it good to understand this stuff even if just for pure knowledge.

[@atomicdmt8763]

well done............ this certainly rounded out various concerns

[@engelbertmaier2853]

I contradict, it was a very exiting and very educational vid. It helped to understand things much better! Thank you, and keep on to your excellent teacher Performances. Greetings from Germany.

[@SchrodingersBox]

Glad you enjoyed it! Then again Germans are known for their scientific and engineering mindsets so maybe not so surprising. Happy holidays!

[@JrSpitty]

This is probably the best video i have found explaining fuel trims! Keep it up! So many videos explain fuel trims and how they respond to each other, but they don't explain how they would be interpreted in a real world situation. This is by far the best video on the web! Explained the discrepancy you would encounter and why you don't see fuel trims move in the hypothetical way extremely well! This definitely helped me understand why you can see both LTFT and STFT trending positive but settling at a specific point, because the computer is using its adaptive learn under a preset. So under idle if you see a higher fuel trim that might be completely normal according to the engine management vs when you are driving down the road. LTFT is the learned average assuming it has had a chance to fill in that cell, where STFT is an adaptation based on engine management and current conditions. So perfect zero is not always realistic or should be seen as a problem. Which can get really confusing when you compare fuel trims with a faster reacting wideband vs a slower reacting narrowband o2 sensor. Thanks a bunch! Keep on makin them dank videos.

[@SchrodingersBox]

Thank you very much!! Yes I believe I scored a winner with this one lol. It’s even used in some automotive tech schools as part of the curriculum.

[@aninullahfaizy2564]

Once again one of your best video you were Wright those two engines secret videos help me to understand this one thank you sir for all your unique videos.

[@davedunington7637]

Thank YOU .... Well done... I appreciate your efforts.

[@Geekdiymechanic]

Great video. Although a simple and commonly used computer control concept, it is difficult to explain and visualize, you did an awesome job. My comment is that the PCM algorithms utilizes either an equation or ROM table(normally this) to determine base value and then adds LTFT and STFT. In this discussion you are talking about fuel, so the PCM has an internal values set up by the engineers for each cell representing fuel injector duty cycle, usually derived from characteristic equations of the system being controlled but implemented as a table. The LTFT table and STFT are used to have the PCM adapt to changing car conditions, sensors and actuators aging or injectors getting dirty for example, by either adding or subtracting from the duty cycle for example. You stated this. What I'm adding is that the PCM has internal non-changing values of which are tweaked at run-time by these dynamic learned values. And this technique is used for other PCM controlled activities, like timing curve, fuel, idle adjustment, shifting, .... From the programming angle, the reason multiple dimensional arrays are used versus always calculating the base values is that the desired value can be determined in constant time. For embedded engineers writing a PCM that controls a motor in real time, this is a very important factor. In addition, using this technique, a lower powered processor can be used or CPU cycles can be devoted to other activities. And, lastly, changes to the engine specification can be done easier using tables versus having to re-develop and test new internal characteristic equations. So, the whole motivation for this comment was to point out that these base values are what are manipulated by performance chips and PCM tweakers,.... I hope I was able to explain what I had in mind. Like I said, this algorithm is not easy to state in a short paragraph or video.

[@sinegra30]

Agree with you but let me point out that you're describing a condition of the ECU during open loop, I mean the ROM tables in the ECU with non changing values are just used under open loop or in case there is a sensor failure like CPK or CMP, the ECU uses this values for limp home mode. I think PCM Tweakers actually manipulate both values those fixed ones for open loop by the engineers in the ECU ROM and those once the O2 Sensors are trimming during close loop condition.

[@alanreyes24]

Exellent video & Thank you for sharing your knowledge with others; even though, this is a difficult topic to learn, I like to challenge myself to improve my knowledge in cars!

[@andrewk778]

This was one of the best videos I have ever watched. This video, as well as your other videos on understanding have made me a better mechanic. The devil is in the details, and this detailed breakdown on how the system operates helps me immensely. I enjoy Scanner Danner, as well as a few others, but YOU are the best.

[@SchrodingersBox]

Thanks ANdrew- this is my favorite and most important video on the channel for sure. But I can't hold a candle to Danner!!! That guys is like Jesus with a Verus lol!!

[@SchrodingersBox]

***** Yeah I usually try to keep it a bit more practical but still technical and not go as much into the theory but no doubt, undersdtanding the theory offers far more enablement to understand all systems and even future systems. Once you understand electrical theory, ALL systems have to follow those rules on way or the other so you have better insight to them right off the bat.

[@alanreyes24]

Thank you for sharing your knowledge with others; even though, this is a difficult topic to learn, I like to challenge myself to improve my knowledge in cars 👍👍

[@RobertoSantiagoRodriguez]

Great video, came to try to understand the adaptive part.😀

[@drbsr1948]

Thanks Matt, That was a great Video.

[@ahmedzidan3455]

Great explanation matt thank you so much

[@labradormcgraw]

For the ultimate understanding of fuel trims, this video has to be studied in conjunction with the original series (parts 1&2) and also with the advanced fuel trims video on the pay channel. As a set, these videos comprise the most informative tutorial on the internet.

[@GalderSander]

Hello, and thank you for a great video about adaptive fuel mapping. :) I would love to see more advanced video about fuel map layers in the ECU. Also more about how the closed loop system responding on faulty conditions in the engine. I have worked a lot with the old Motronic systems from my old BMW straight six engines, and with my old degree in electronic I have managed doing well. I have never changed a part in any of my BMW just for the try. I have always trusted my volt/multi meter and good reasoning. However on my newer BMW engine it's harder to see the big picture, or at any newer engine in fact. So this input from you really helps a lot. To the summer I will finish my engineering degree in Automation and system control and I really love the beauty of engine management and regulation. Looking forward to more juicy stuff from your channel. Greetings from Norway:)

[@allusernamestaken01]

Oh man, it helped me a lot understanding fuel trims!

[@taildragger1197]

I doubt I ever need this info but it was informative and interesting. I never thought about the "map" being three dimensional. Good to know If I ever have a weak but still functional fuel pump. Yes I do need a life. Thanks for pointing that out.

[@Cavalier_Steve]

Wow watching this video has helped me understand what all the graphs are that tuners are looking at when tuning a car thank you! Also I have learned that as a DIYer I need to get a life. Lol thanks Matt once again for an excellent video.

[@pdj1968pj]

great video starting to understand ST and LT readings and on some of your early O2 videos help me understand how they work. Keep them coming, for one catman to another 'l'

[@REDNECKHOOSIER1]

I'm going to have to have a staff meeting in the morning and show them this. Thanks again for another great video. While it all made perfect since to me I don't think my guys will get it. I'm about the only one who does fuel trims for this reason. Excellent video Matt.....

[@bradybell6129]

"I'm about the only one who does fuel trims for this reason. " Job security. :=)

[@TheGeno2001h]

Thank you for your time

[@nadeemahmed640]

Thanks sir appreciate your efforts.I am from Kuwait and i always watch your videos .

[@pathassett1495]

Great explanation. I've actually found that sometimes when I fix a major vacuum leak that I have to completely reset the pcm because after doing the fix, trying to run a key on engine running test on some vehicles the study will be so negative that the computer can't get the o2 sensors to switch during the test. This happened on a ford excursion that only had the maf wire plug that sealed the air box housing was out causing a massive vacuum leak after the maf sensor. Again, I found that you explained this really well.

[@SchrodingersBox]

Yes this would indeed expected - the reason being not only the fuel trim relearn that must occur but also the IAC relearn which will be very significant after a vacuum leak is fixed. It is easiest for the relearns to start with the default cells rather than to correct from the adapted cell adjustments.

[@andriyselezen9513]

Thanks for the information . That was something new and interesting

[@SchrodingersBox]

if you found this interesting then you found the right place!!!

[@paulmvn5431]

I should have watched this videos sooner. I never knew which Fuel Trim to look at and was always hoping for a Net Fuel Trim PID. Thank you!

[@SchrodingersBox]

Paul MvN I have never seen a net trim PID but even then it would be useless- the value in total trim comes from the difference in the ST and LT. For example if net trim was 50 and LT was 25 and ST was 25 you know you have maxed out fuel trim and this drastically changes your interpretation of O2 sensor output as opposed to if LT was 50 and ST was 0

[@paulmvn5431]

true, but I didn't know that before this video. :)

[@aor3200]

Wow. Before this i thought, well i kind of understand fuel trims. After this.. hmm, not really. Excellent demonstration, sir.

[@TheEgg185]

Dunning-Kruger effect. The more you know, the more you realize how much there must be that you don't know.

[@MrJoelerb]

Great video I run heavy equipment for 12 hrs a day so I have tons of time to listen to your videos and learn while I work I had to chuckle when I heard you tell me I had no life lol

[@SchrodingersBox]

MrJoelerb hahaha you read my mind, but others have said same about me bro. This is life, at it's best!

[@nokalamaduna2709]

Matt, I finally saw this video and now I can say I understand what the guys are doing when they play around with those numbers during a car remap. I didn't understand even a bit what was a remap all about, but with this information, I now understand exactly what they are doing but I am still skeptical about sending my cars for that remap due to not trusting. Thank you so much for these videos, I always watch them until the end, it's interesting to work on these new cars.

[@SchrodingersBox]

congratulations on your new understanding! very few people invest that kind of effort.

[@nokalamaduna2709]

@@SchrodingersBox Everywhere I come across someone who calls himself/herself a mechanic, I ask what is short and long fuel trim, mmmhhhh, now one knows that, I think am about to be one of the best mechanics in South Africa. 😀😀😀

[@SchrodingersBox]

Yep. That’s the difference between someone who- like everyone else- can turn bolts and someone who diagnosis the first time.

[@richardgordon5001]

I have been a Mechanic for around 25 years and i must say your videos are great i have learned so much especially about air fuel sensors ! i understood o2 sensors and knew how to use the data to help diagnose the issue with the car but A/F sensors threw me way off ! your video was invaluable for understanding them better .! you not only have a great amount of knowledge and others do as well the difference is you have a gift of being a great teacher ! yes teaching is a gift ! i have met many people who are very very smart and knowledgeable but could not teach anyone how to make a sandwich ! You do a wonderful job at explaining the subject from the very basics at the beginning and work your way through the subject with great detail and thought into the best way for it to make sense as any good teacher will do ! Thank you for passing on your knowledge to others that's why i am willing to pay for your full version it's more then worth it ! Tech students in automotive this is a must ! you will most likely learn more on here then in the classroom at least get the best of both if i could go back and this was around in the early 90s i would have had a much easier time of learning ..Great Channel !!

[@SchrodingersBox]

Wow thanks man!!! What a nice compliment!

[@felixsoto9110]

Love your videos

[@nilushamadumal3695]

The best explanation ever I found..thank you sir

[@SchrodingersBox]

You are welcome!

[@slyfpv]

very usefull ,thanks a lot for your work from Quebec

[@WasimAkram-dv1ch]

Woaah!! Watched it like three times. You're awesome. Keep such topics coming Sir.

[@SchrodingersBox]

Wasim Akram 3 times???? OMG, I think you need professional medical help lol!!!!

[@WasimAkram-dv1ch]

Schrodingers Box​ hahahah can't just get enough i love to.know how my car works

[@graphmastr]

awesome video, not only did I make it through the whole thing I fully understood it and took notes in my textbook, because I am a automotive tech student going to UTI in sacramento, CA. This video along with your other fuel trim video made an awesome educational supplement for the material we covered today. My current course in introduction to driveabilty and todays lecture was electronic engine management (sensors, actuators, ECM-PCM, and STFT/LTFT) I can tell you from having studied thoes things the past feew days and wastchi9ngt your video you are teaching industry standard procedures. You, scanner danner, and eric the car guy along with scotty kilmer make up my group of professors at KZbin University. Keep on rocking

[@bradybell6129]

From having seen several of his videos, I imagine that he would agree with three of your four choices.

[@SchrodingersBox]

You talking about using Scotty as a resource... or living in California lol? because I wouldn't do either! man I just don't the scotty thing. "Hey your car doesn't blow cold air?? Here's how to recharge your A/C system!!" Dispicable.

[@nandanalal5072]

Excellent brother

[@johnphillips1001]

Damn, i followed every word and had some fun listening to you 😁 👍 not hard for me , easy as , i even thought looks like low fuel pressure just b4 you said

[@DJDevon3]

Fuel maps are learned and can change depending on A/F for the purpose of fuel efficiency. Everything it does is for goal of keeping the best MPG it can depending on the situation. Fuel maps use an adaptive algorithm. Fuel maps vary by manufacturer too. You'll never fully understand every manufacturers maps there are simply too many but the basic principle is the same. Also depends on what components and sensors they use like electronic IAC vs mechanical and so on because different components will react at different speeds. PCM chip and network bus speeds also play a role and why some cars seem to react slower than others. Older vehicles generally have slower chips but the change shouldn't be a difference of minutes but in seconds. Like 2 seconds vs 4 seconds it's not as dramatic as minutes that you make it out to be. Each fuel map is designed specifically for the ECU. One of the best things you can do to avoid triggering an adaption is to inflict quick changes. Blips are ignored and not adapted to. However if you sit there and hold propane in it for a minute or two it will indeed start to relearn and remap the cell except in the case of it being too far lean to come back to stoich as in your Jeep example. ECU/PCM's are pretty darn smart. Another major part of the fuel map is the startup idle enrichment map. It slowly subtracts fuel and adds air as the engine and IAC warms up. You can't really use it for diagnostics since it's in open loop but there are plenty of other sub-sections of the fuel map. Bless me I watched the whole video. :) Good video. :)

[@SchrodingersBox]

***** Absolutely correct. It is incredibly complex and I agree 100%- delving too far into this will put you way deeper in the forest than you need to be, or even want to be. This milieu is more for design than it is for repair and diagnostic.

[@DJDevon3]

juergen scholl Fuel maps and fuel strategy is not emission based. They are for fuel and engine efficiency. Emissions are a variable not the goal. Yes there are emission laws that must be met but that's a secondary goal compared to performance and fuel efficiency. There are many goals.

[@DJDevon3]

juergen scholl Wow. You really don't have a clue about half of what you're saying. How old are you? I hope you're younger than 25 because you still have a lot to learn.

[@DJDevon3]

Glad you're impressed. Thanks. I have multiple approaches for multiple kinds of people.

[@vwalker9315]

Nice Video man Thanks for the education

[@rheidtech]

I really learned alot. Thanks. Made it to the end whoohooo!

[@DENicholsAutoBravado]

R HEIDEMAN I did take a break at 27:00. :)

[@HuyLe-mx6to]

Hi Matt, I've been watching your videos and DAMN you're good. I'm no mechanic, not even changing part person. I just wanted to DIY my own troubleshooting on my cars. Luckily, I had computer science knowledge and construction background as well, therefore you made it so understandable. DAMN, you're good, logical, easy to understand, deep learning which I'm looking for. The videos help me alot, I didn't know anything til I watched your videos. Again Thanks. Keep up the good work, and I do agree alot of mechanic just want to replace parts... Thanks again.

[@SchrodingersBox]

Thanks my friend. This video in particular takes a pretty specialized person to appreciate. Glad you found it and appreciate it.

[@rogereastman3187]

It's ALWAYS helpful

[@adrianapollyon5087]

Very exciting video

[@SchrodingersBox]

Thanks!! I never thought of it as exciting lol but that’s a great compliment

[@playpaltalk]

Nice video thank you

[@night4lover]

Great video keep it up, this is starting to make sense. I was confident in the simple explanation of fuel trim in the earlier videos. And I now see that there is basic model for this behavior or a general organizing principal for observing the data in context. So great you see how it helps me and many others with gathering focus on important concepts like this. About this model. I will be assuming that their are published info and there is an industry specific standard software library available. Your explanation in this video should help me to avoid the wrong assumption when I take a crack at automotive live data analysis which is what I'm working to understand. And I think I'll probably still remember how to change a part -even- when i can determine its malfunction beforehand. If that sounds like I worry... You can just remind me It's like riding a hippo sometimes you underwater and sometimes your not, but mostly you wind up a stuck in the mud.

[@SchrodingersBox]

Great comment bro. Regarding the "library"- I am sure there are softwares to see maps for individual fuel cells in an array but I actually have never seen one- not even in a factory manual. This is all programming-related, probably not things you'd find in service related literature.

[@mechanic4226]

thanks. Good stuff, keep it up

[@JD-526]

Great explanation of XYZ of the info.

[@wmichaels362]

Good job explaining a complex subject. GM relies on Freeze Frame/Failure Records to help the mechanic/tech identify the lean or rich conditions that set the Fuel Trim DTC (likewise with other DTCs).

[@ZloB1N]

Priceless even after 7 years

[@SchrodingersBox]

Thank you!!! it’s still the same concept even today only the arrays are way, way, way more complex than when I made this video!!

[@BobC777]

My big takeaway from this was the fact that there is an array of LTFT values and not just one for the system. It makes a lot of sense. Thanks so much for all this!

[@SchrodingersBox]

that’s absolutely correct!!

[@SteveRobReviews]

That was awesome . One word that drives me crazy our friend ScannerDanner says after a deep subject like you just did is - "variables" Ha - just when you think you got it down (WHAM) - oh yeah there are variables you have to take into account. I have no idea now what the fuel mapping strategy would look like on a wide band . Now we have to consider the downstream O2 into the mix, another "variable ". Mapping strategy is only as good as the sensor inputs and if their defective guess what another "variable " I do know clearing codes does not reset everything on all models oh yeah more "variables " There's such an advantage with just working on one brand . There are no variables in your vid quality Matt , your very consistent. 👍👍

[@SchrodingersBox]

Steve Rob Hahaha Variables, Steve you have no idea. Variables are my world. I see everything in life as "uncontrolled variables". Everything. I am always seeing inconsistencies. I am sure it will have severe mental consequences over time!!! Variables are to scientific thinking as ants are to a picnic. They ruin everything and you have to eliminate them... well actually all but one, so maybe the picnic analogy is not really accurate lol.

[@billyr9840]

Schrodingers Box Severe mental consequences over time ! A lot of time must of past, because I can see those consequences in your humor. LOL ! Father Matt, bless me to, I watched the vid to the end! Great stuff for the guy who his really trying to understand fuel trims and use them.

[@ThunderbirdRocket]

Schrodingers Box yeah me too

[@tepesrazvan7010]

Thanks man, extrem advance informations

[@hondagamer79]

Thanks it's so much useful

[@SchrodingersBox]

Glad to hear that!

[@jabsage155]

U make a lot of sense thank u

[@cobraninetysix3883]

Great Video! Designed fr the advanced DIY'er.

[@djkelectrical]

Just to reiterate a point to my fellow viewers about liking or giving a thumbs up to videos. The information contained within the videos on this channel is always highly informative and delivered with enthusiasm and wit. Please don't forget to like them - if you do. In the past, and irrespective of channel, I admit that I am guilty of finding some videos so engaging that I feel motivated enough to comment only to forget to like it! I do accept that this process may be unique to my grey matter but I thought I'd mention it anyway.

[@SchrodingersBox]

djkelectrical Iappreciate that and take it as a tremendous compliment!!

[@EddieTheGrouch]

Thanks for the heads-up on 3D fuel tables. I didn't think they were that complex. Are there really discrete vertical cells or is the base table offset by programmed amounts based on MAP, IAC, etc at the time of sampling? I can see either being used. I was surprised to learn that the PCM uses the LTFT table before live data but I guess it makes sense as performance lag is reduced since the PCM is not constantly sampling and correcting each cell until a threshold is reached just like a threshold has to be met before setting a cell value in the first place. This sure explains why a car can run like poop for awhile after a PCM swap or reset - especially if the problem that filled the old PCM's cells with correction data is not fixed and all the old corrections need to be re-learned. I admit I don't always think to hit the LIKE button. When you watch enough good videos like yours ya tend to set the bar high and take it for granted and then wear out the DISLIKE button when others don't meet that high standard. I pressed it this time, though! :)

[@DENicholsAutoBravado]

Eddie the Grouch I do push the like button a lot since I choose to watch channels that are more often worth my time. If something really blows my mind, then I put it on favorites. :) I should do that with his more recent video on the truth about oxygen sensors.

[@simoncrane8267]

Interesting Video there Matt mate. The biggest thing I took away from it was a better knowledge of when it is prudent to wipe the map, or leave it as-is. Also your observation that under certain conditions, there will be cells on the map with zero trim, that are so because that cell(s) have not been used yet since the last wipe, was a minor eureka moment, which tied up a loose end question (I love those) I have often graphed long/short term fuel trim under normal driving conditions, and observed the changing long term values, but never through the lens of a more thorough understanding of the fuel map. Now I see there is diagnostic value to test driving the vehicle with the map as-is, and after clearing, and comparing the two graphs. And, if you wipe the map, it is like the fault (eg vacuum leak) has just occurred, and you can see the short term trims working hard to correct the problem, generating a very definite graph, which is always easier for diagnosis. 50% of my work is on BMW`s, and they use the term "adaptions" to describe fuel trim. There is, on most scan tools, a facility to "clear adaptions" which saves having to disconnect the battery, with the attendant nause of having to reset clocks and radio stations etc. Top Notch , carry on....

[@SchrodingersBox]

Simon Crane Top notch comment sir! I am always amazed at the number of people like me out there who eat this stuff up. It's remarkable!!

[@simoncrane8267]

Yeah, kinda restores your faith in humankind a bit doesn`t it ?? :-)

[@MarzNet256]

Excellent. I think another way to think about it is to look at the first oxygen sensor as a quality control system for the fuel map. If sensor is switching rich to lean for a given set of RPM, Load, and MAP values, then the LTFT value in the table is correct. Otherwise, the PCM must adjust LTFT value in table to get the 02 sensor "working", a.k.a switching again, and this will be accomplished by changing STFT.

[@SchrodingersBox]

Well said!

[@andreagili4589]

Fascinating

[@SchrodingersBox]

Andrea Gili It is ain't it. Its very complex but yet at the same time it also simplifies a lot of things and removes the "mystery" behind fuel trims.

[@charlesdowns1691]

interesting+ i watched it all.

[@randymarion5767]

Matt - this was an EXCELLENT video... answered so many of my questions I had in the back of my mind as to how the LTFT graphs could and would change so quickly in some of the diagnosis I have viewed on your channel. And the info on the Z axis dealing with MAP cleared my confusion on how it was possible for me to take my car from Ohio (800 ft) to the Rockies (8000 ft) and still run well... I am still a little foggy on what would clear the map.... the clearing of any check engine code or only certain codes?

[@SchrodingersBox]

Yes your understanding is very clear (the Z map does explain the altitude adaptation!!). Clearing the MAP is done anytime the PCM is cleared either through absence of power for a few minutes OR through using the code clearing function on a reader or scantool.

[@jasonthetalker7253]

This help explain tuning for racing

[@SchrodingersBox]

very much so. And how ricers have no clue what they are doing most often lol

[@themrrd12345]

Been watching the videos, I keep learning from you. One thing I didnt really catch though was in a rich condition. I have both banks on a v6 running very rich according to the ltft about 24-25%. The stft on both banks is close to 0%. I know it is not o2 sensors from your other videos since it's both banks and they are oscillating normally. I cleaned the maf already. Not sure what else to look for.

[@SchrodingersBox]

Check EVAP, Fuel pressure, EGR and induction sensors. ANything thart either is adding unmetered fuel OR is undermetering the induction is where your thinking should be on rich conditions.

[@aminullahfaizy6154]

No it was useful sir thanks

[@Highdensity89]

Hi Matt, thanks for taking the time to make all these videos; I haven't watched them all yet but I will. I have a question in regards to the fuel trim, adaptive fuel learn strategy, and two foot drivers on automatics. My uncle has had nothing but problems with his new 2014 f150. Most of his problems consist of transmission issues (slamming into gear). He's taken it to the dealer multiple times with no remedy. So he decided to switch from a ford to a chevy. He's currently driving a chevy silverado automatic 4x4 and having the same problems with the trans. He has more issues than what I'm naming here, I know both vehicles run rough at times. I'm not really looking for an answer here, I'm just looking to see if my hypothesis could hold some answers. For a new automatic vehicle, with fuel trims being made through the reaction of the gas pedal, is it possible that a two foot driver (in short terms) screw up the fuel trim and then the adaptive fuel strategy? Would that then screw up the engine's signal to the transmission to shift properly? Sorry if this doesn't make any sense, I was just watching your video and this popped in my head. I know there's more variables to consider. I was just wondering in a short term if its possible. I will gladly take any humor or seriousness with this, thanks again for your time.