How to use Fuel Trim to identify the cause of a P0171 and P0174 code

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How to use Fuel Trim to identify the cause of a P0171 and P0174 code

Рет қаралды 174,787

Күн бұрын

In this video I will show you how to use trouble codes, freeze frame data, short term and long term fuel trim data to determine the type of lean condition.
Engine Performance Diagnostics chapters 4 and 5
Symptoms
- rough idle
- higher than normal idle speed
- lower than normal idle speed
- run good under load
- check engine light (P0171, P0174)
Fix
- repair vacuum leak at the EGR tube
Tests shown
- how to use freeze frame data to determine type of lean condition
- how to read and interpret fuel trim numbers (STFT and LTFT)
- how to locate a vacuum leak with a smoke machine
- how to use idle speed and desired idle speed data parameters
Playlist
- (Chapters 4 and 5) Fuel Trim and Oxygen Sensor Testing
• (Chapters 4 and 5) Fue...
Related videos
- False mass airflow sensor/idle control system codes - vacuum leak - Pontiac
• Why the MAF "unplug it...
- P0507 Idle Control System (RPM Too High) - vacuum leak - GM
• P0507 Idle Control Sys...
- Understanding Short Term and Long Term Fuel Trim (an SD Premium video)
• Understanding Short Te...
- Causes of lean condition trouble codes P0171, P0174 - GM 5 3L
• Causes of lean conditi...
- Ford F-150 P0171 P0174 Trouble Codes - vacuum leak (water test)
• Ford F-150 P0171 P0174...
For more on understanding and using fuel trim go to www.scannerdanner.com
I know we have done this before, but seeing it again in a different situation is good re-enforcement of the topic.
For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium www.scannerdan... There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!
Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.

Пікірлер: 223

@ScannerDanner 12 жыл бұрын

glad you liked it. I've had it on my hard driver for months, just thought I covered this before, but I figured what the heck, I'll upload it anyway. It is a good review of fuel trim diagnostics

@kevinshannon955 4 жыл бұрын

ScannerDanner If my LTFT is between 20-25 and STFT is down around either side of zero, what would you expect is causing that?

@SchrodingersBox 11 жыл бұрын

Love your videos and E-book! Would love to see your approach on a vehicle with Air/Fuel sensors someday. I remember you saying you're not famliar with them, however if you do a video on them we'll all learn including yourself!

@pabloarevalodelaguila8767 4 жыл бұрын

THANK YOU MASTER FOR SHARING YOUR KNOWLEDGE I HAVE LEARNED A LOT FROM YOU.

@ScannerDanner 4 жыл бұрын

You are very welcome

@paulfiebke3909 3 жыл бұрын

I need get me a smoker bad i could, i had turna job down over not having one. Keep up the good work

@ScannerDanner 12 жыл бұрын

It is possible, take for example a system running on 10 psi of fuel psi when it should be 50. Fuel trims will be positive across the board. I just use the RPM/Fuel trim comparison as a guide. I certainly follow it up with further testing to be 100%

@jimhenderson8571 6 жыл бұрын

Love the videos ... you really provide clear insights as you're going through your diagnostic steps. I have a 1997 Chevy C-2500 with the 7.4L engine. I bought it used with 220K about 18 months ago. Recently and very abruptly, the truck began with a series of symptoms: == rough starting, sometimes having to crank 3-4 times == very rough running while it warms up == strong fuel order == hesitation from stops (stop lights and signs). I picked up a Harbor Freight OBD scanner w/in my budget (the truck cost less than $1k). When I checked the freeze frame for the two trouble codes the truck is throwing, I found the following: Calc Load 3.5% ECT 203.0 STFT B1 36.7% LTFT B1 25.0% STFT B2 35.9% LTFT B2 25.0% MAP 9.4 Engine RPM 1159 Vehicle Speed 34 mph MAF 1.58 (lb/min) TPS 1.9 Does this look like I'm looking for a vacuum leak? The STFT numbers are WAY higher than I've seen you discuss in the videos I've watched, and the LTFT numbers are bad too. Where should I be looking if I'm looking at a vacuum leak?

@ScannerDanner 6 жыл бұрын

you most certainly have either a severe lean condition or you have some oxygen sensor issues. We need to fist confirm that your O2 sensors can react to ratio changes. With these fuel trim numbers, your O2 sensors should be flatline low voltage. Snap the throttle rapidly and force the ratio to go rich, O2 sensors should react on both banks and rise to over 800mv at some point in time. Now if your fuel pressure is low or you have some other critical sensor failure, this "snap throttle" test may fail. In this case, add propane to the intake and force it rich and watch for the reaction. If you O2 sensors are fine, then we can proceed. You symptoms suggest it is NOT an O2 problem but let's cover our bases anyway. When you say rough starting and you have to crank it 3 or 4 times. Is it starting and stalling or not starting at all until the 4th try? The freeze frame data does look like a vacuum leak but it could be something else. I need fuel trim data with the engine warm, at idle and at 3000 rpm, in park, no loads. Hold it at each position for at least a minute before recording that data

@anyheck 12 жыл бұрын

Clear, methodical and excellent as always. Thank you for sharing your knowledge.

@schrochem 11 жыл бұрын

Just wanted to say thanks for this video. I'm new to using a scanner and wanted to know why my mpg dropped so much. I got this exact same data.....So I went looking and found a tube I forgot to put back on it's nipple when I replaced my head cover gaskets....doh! MUCH happier now. Thanks.

@d.l.horton2093 5 ай бұрын

I always enjoy your videos when I am looking to fix something. They always add insight to what I'm working on.

@lifeInProgress_8020 12 жыл бұрын

I have rarely seen a vaccuum leak cause a fuel trim issue at idle. I'm a 15 year japanesse tech in the field. On the Toyota vehicles, I have seen many time over it was a MAF sensor and on the Subaru it can go either way, (impreza and outback for the most part). So I usually go after the MAF first by doing a snap test and visually inspecting the hot wire. Like a vaccuum leak, Long trim improve has the RPM goes up, but that not alway the case also. I guess my point is, always verifty your diag.

@jay7264 12 жыл бұрын

Man paul is an awesome tech. I recently repaired a integra that had a no start. I used your technique on the main relay if i made enough on that job i would paypal you the money your awesome

@starless9 6 жыл бұрын

I'm having the same scenario in a 2003 mazda protege5 - LTFT ~ 25% @ 700rpm, LTFT ~ 7.8% @ 2000rpm, LTFT ~ 3.4% @ 2500rpm. Not sure I follow why this has to be vacuum leak related - but will try to find leak. Anyways, this seems very in depth and professional. You should have more views!

@starless9 6 жыл бұрын

So, at idle/low rpm air demand is less, the air from leak bypasses MAF and makes up a large proportion of airflow to engine. Upstream O2 senses combustion is lean, and ECM ups LTFT to compensate. But at high rpm, air demand is more, air from leak is less in proportion and ECM sticks closer to its normal program of 0% LTFT... is that right?

@worldcrafter 6 жыл бұрын

perfect analysis and explanation. thank you for the great tutorial

@12mak 5 жыл бұрын

You are such a GREAT instructor. Thank you for the explanations.

@swiftymorgan2210 5 жыл бұрын

Very very good explaination and live data showing of all relevant terms

@craneandsonlawncare8050 4 жыл бұрын

Yet another great educational vid. Thank you sir for taking the time to make and post this. Every little helps for the DIY mechanic.

@ScannerDanner 4 жыл бұрын

Thanks for watching!

@workfrompae2818 4 жыл бұрын

I have purchase your book. It is a very good book. With out your book and your videos I would be lost and couldn't figure where to start from a beginer or entry level mechanic. I'm from Thailand by the way. Sorry for my poor english.

@ScannerDanner 4 жыл бұрын

your English is great! Thank you so much. Stay with me, I promise it get's better and better the more you understand these fundamentals

@ScannerDanner 11 жыл бұрын

I will work on that my friend and thank you so much for your support

@sergiot6206 5 жыл бұрын

I'm impressed! We have no good diagnosters in my city( I'm trying to realise what the problem is with my MB w203 by eml scanner,changing tubes, fog tests. But still no result. Sure that ScannerDanner whold fix it for real!

@JoelAutomotiveInaction 9 жыл бұрын

thank you Paul, I have a 200 Chevy silverado 4.3l is making crazy is my brother truck, it has misfire only on cylinder 4 and in between 1800 to 2800 rpm only seating or driving. no under load only in between those RPM, I replace the crank sensor because it was doing contact with reluctor and shimmed,did ckp variation relearn, updated timing chain to tensioner style ,I remove the distributor to check the gear was worn I replace complete unit including cap and rotor cam sensor,no changes I updated the injectors to multiport ,no changes has new sparks plugs and wires everything are factory parts, so talking to a teacher who works at gm dealer for 20 years told me you will have exhaust valves leaking , I used pressure transducer , did cranking and running and leak down I did not see any significant differences at all no more than 8% leak down,I comment to the teacher and he said still are valves so I decide to removed both head cylinders send them to machine shop for complete valve job they open clearance on valve guides installed back and guest what my misfire is there exactly at the same Rpm, I have created misfire on different cylinders and the pcm identified the cylinder correctly.please base on your experience let me know any Idea if I am missing some thing ,I appreciate your help.

@felplayvina 12 жыл бұрын

great video Paul, finally I do understand fuel trim..thank you..

@ScannerDanner 12 жыл бұрын

Watch my "Dirty MAF Case Study" Fuel trim is normal at idle and positive at higher RPMs, exactly opposite of what a vacuum leak does. The only real exception to this rule is with speed density engines (non MAF systems). Vacuum leaks on these can have normal fuel trim numbers at idle.

@1130brent 7 ай бұрын

Thanks for the information. I’m not sure this matters as I’m still believing this applies because my barometric pressure is indicating I’m at a higher altitude (1000) than what I really am (500) which I think also points to maf, however I must correct something. The ltft is not starting off normal. It’s starting high at around 20 and going up to 30 with increased rpm’s. It’s also almost all at once going up and not a gradual rise.

@a2z_farm 7 ай бұрын

Great job . Great layout . Be blessed Richard Iowa

@ekbadturk 8 жыл бұрын

Hi SDl thank you for all your uploaded videos they have been great and helping me to learn more about cars and also has helped me in my ASE tests.

@ScannerDanner 8 жыл бұрын

awesome! would you mind posting that to my website? www.scannerdanner.com/customer/feedback#add-comment

@ekbadturk 8 жыл бұрын

+ScannerDanner it is the least I can do for you no problem

@ScannerDanner 8 жыл бұрын

thanks so much!

@suhaibchobi Жыл бұрын

Super clear explaining. Thanks

@luxurycarpets4028 5 жыл бұрын

Appreciated 👍 very well done and good explanation very simple and to the point . I have a problem if you can help me out please , It’s a Range Rover sport 2010 3.0 diesel. 1-Starts straight away 2-engine light is on and it’s on limp mode 3- throwing code p0193 4-change the high pressure fuel rail including the sensor 5-changed map and maf sensors 6-car won’t rev past 3 7-max speed goes up to 70mph 8-drops the rev and speed when going uphill 9-sometimes on a flat road it drops the speed to 20mph and rev won’t past 2 10-recently got it services and changed all the filters including fuel filter . 11-i have got a cheap OBD scanner and saw a fuel pressure on live data it shows 22000 and it’s still won’t go up and down when rev . 12-when sudden floor the gas paddle it will drop the speed rev won’t go up it feels like fuel not coming or exhaust is blocked ,fuel or exhaust system feel squeezed .but if rev it slowly /gradually then it picks up speed until I floor the peddle but when release the paddle half way up then it feels bit of ease . 13-sorry for the very long message but I wanted some help desperately and wanted to describe as much as possible .been to land hover specialist and few other garages but no joy ,some say it’s an electric issue and some say it’s a high school reassure fuel pump and some say it’s a turbo or pcm issue but no 1 is able to figure it out exactly .. ( I have a short video uploaded as well on KZfaq ) any help would be appreciated.👍

@Nztimr33 11 жыл бұрын

Great video there very informative and good to see you nailed it with the smoke machine to back up your theory!

@ScannerDanner 12 жыл бұрын

and thank you for the comment!

@freddybernabe9599 Жыл бұрын

Yes! Lets go!!💪🏽👨🏽‍🔧🔥

@SEXYTECH1000 12 жыл бұрын

EXCELLENT VID AND DIAGNOSIS BRO!!!!!!

@ravit928 Жыл бұрын

Outstanding. Don’t have a code my trims behave the same

@lifeInProgress_8020 12 жыл бұрын

your right I don't what I'm talking about :). you should make a vidoe post on how to daig. so everyone here can be smart like you! :) ;)

@m11ny 5 ай бұрын

Ive got different numbers, my STFT are low at idle & climbs up & spikes to +25% then drops back down to 10 for some reason, when accelerating and usually at constant speed around 3,000rpm

@ScannerDanner 12 жыл бұрын

very kind words thank you. just buy my ebook and that's enough of a thank you for sure. and if you already have it then you've done enough for me already. :-)

@ScannerDanner 12 жыл бұрын

great! Thanks

@SteveRobReviews 12 жыл бұрын

Well done. seems odd to have a gear clamp around the egr valve ?

@servicewriter2905 4 жыл бұрын

Love your classes man. I would like to purchase book as well to support the channel.

@ScannerDanner 4 жыл бұрын

Awesome, thank you! You can find it on my website at www.scannerdanner.com

@AUTOTUB3 Жыл бұрын

Awesome!

@Carlitosway211 7 жыл бұрын

Rubber bands and latex gloves work great for sealing off those throttle bodies.

@erikwright197 Жыл бұрын

What would be the cause of a LTFT staying at 23-25 when car is warmed up and idle at 3000 rpm?

@ScannerDanner 12 жыл бұрын

We bought it from AESwave I'm not sure the name off hand. (Redline maybe?) (smokepro?)

@SMFLEIS 3 жыл бұрын

Thanks

@SMFLEIS 3 жыл бұрын

I need some help 2011 Ford ranger 4.0 Po174 and 171 I smoke tested and egr leak at valve. replaced valve no other leaks found. Still high fuel times 25 and 24 long term trim. 60 psi fuel pressure. I’m at a lost . Thanks for any help you can give me

@ScannerDanner 12 жыл бұрын

It depend on the manufacturer, not the scan tool.

@andrewthompsonuk1 7 жыл бұрын

60 years old and still doing the job it was designed to do. I suspect it is far easier to keep that thing going than most modern cars.

@Carlitosway211 7 жыл бұрын

What are you talking about?

@NobodyAskedForThis 6 жыл бұрын

Andrew Thompson I don't think Danner is 60. Haha

@oldskoolfunk71 10 жыл бұрын

Hey Dan I have 99 Mazda 626 2.0L no fuel trim readings at all (using actron scanner cp9185) and the car stalls instantly, dead downstream sensor (after cat) when I hit the gas (it only idles) would a dead o2 sensor cause frozen fuel trim? Great work by the way your videos are priceless brother.

@ScannerDanner 10 жыл бұрын

yes, a dead O2 with a hard fault in memory, will cause the PCM to enter an open loop fault mode at times and your fuel trim numbers will not react to any O2 signal.

@oldskoolfunk71 10 жыл бұрын

Thanks for the comment Dan, I appreciate your response.

@semajd5995 3 жыл бұрын

@@ScannerDanner I got 2009 suburban 5.3…I only got code for p0171 for bank one. The short term fuel trim on both banks are 0 or negative…the long term trim on bank 1 is like 20 at idle and increases to about 30 when I rev up the engine. It does not correct itself. Does that mean I have a fuel problem?

@ScannerDanner 3 жыл бұрын

@@semajd5995 most likely this is NOT a vacuum leak, so yes, BUT, I need you to tell me what your trim numbers are on BOTH banks. It doesn't matter that the code is only for bank 1

@NobodyAskedForThis 6 жыл бұрын

Makes perfect sense. As RPM increases so does fuel demand. If the fuel trims did not improve, or got worse, fuel delivery would be suspected. Could you check for vacuum leaks if fuel trims show lean? Of course. Would you have found the problem on this vehicle? Absolutely. But what if the problem were fuel related, which happens often? You'd be chasing vacuum leaks that aren't there. A quick couple minutes can save you hours.

@lf7161 4 жыл бұрын

My short term moves to minus as I increase revs, but my long term stays at 24.2, does this suggest a fuel delivery problem then? I also have 2 "P0170" codes both fuel trim bank 1 , lastly my idle air control valve is bad so perhaps that's one of the fuel trim codes? Maybe I have a dirty fuel filter

@r.weaver3769 4 жыл бұрын

I get no codes, but LTFT is +7% both banks, 2004 jeep 4.0l GC. I get switching on bank 2 sensor 2 no code, soot at tailpipe.Cleaned Throttle body, scanners says cam sync lost. The Crank and Cam sensors appear new. Plugs new, fuel filter new, Fuel pressure 52 psi idle. Low power when passing. Number 4 injector was leaking, I had a set of 4 hole injectors for another jeep I have. so I swapped, misfire gone. but long term fuel trim says between 7 and 9%. fuel mileage low.

@jackwade793 11 жыл бұрын

I would like to see a demonstration of a lean condition at load. Particularly pertaining to a soft failing maf sensor or soft failingmo2'sensor

@yaseenhashim8538 3 жыл бұрын

awesome thanks ScannerDanner

@rashd189 5 жыл бұрын

very nice , thanks

@ScannerDanner 12 жыл бұрын

I think that was holding another bracket or something, I'm not sure, I don't remember

@tomjones4145 5 жыл бұрын

Great video / thank you

@BigEightiesNewWave Жыл бұрын

SD wanted me to check fuel trims at idle and 2500RPM on my Ford Focus. Results STFT way over 20% at idle gets better (less) at 2500. LTFT was stuck at 25% Both O2 sensors passed switching test and I/M readiness passed, but then code P0171 came back and idles rough and then dies. Also, one O2 sensor says max amplitude failed, and even though it goes into CL quickly, an OL-FAULT is showing up. Not a code, just what my rudimentary AL519 Autel shows me.

@ScannerDanner Жыл бұрын

This is where you put that reply...

@AlexRosskopf 4 жыл бұрын

if the long term fuel trims dont get better what is the issue? or some ideas for the issue

@j06c 7 жыл бұрын

i have a ford expedition with a 5.4 engine longterm fuel trim at idle is 15 and goes up to 25 at higher RPMS where should i go. i cant find any vacuum leaks

@BmwMe-uh9sy 5 жыл бұрын

thats indicating less and less fuel as you raise up the engine speed

@degar1877 4 ай бұрын

Have the same issue on my 302 , but at high RPM I’m still reading around +28% on my fuel trim and I smoke the system to see if there was a vacuum leak none found. What could the issue be ? Do have a video on this example? I have a lean code for bank 2 only

@ScannerDanner 4 ай бұрын

If it's a high RPM lean condition, or doesn't improve at higher RPM them is not a vacuum leak. Fuel pressure, maf sensor should be you next two checks

@dougdrefus4274 6 жыл бұрын

Shouldn't I be able to clear P0171 and P0174 with a scanner and now see NO CODES PRESENT which I do and see in data STFT=0 and LTFT= 0 which I don't. I cant get rid of LTFT= 25% KOEO or KOER, even on a cold start. 2005 Yukon 5.3L

@ksich8142 2 жыл бұрын

Hey could a failing fuel pump cause a P0174 in an Infiniti EX35 ? ( Nissan) my fuel gauge is off and I tried cleaning the terminals for the lever on the pump it self but didn’t fix the fuel readings. Could this slowly fail yet still deliver fuel to not stall or not to idle bad ? Thanks

@ReedsAuto 8 жыл бұрын

I have one that is stumping me right now. It's an 81 G20 that we put an 6.0 in a couple years back. Customer brought it back last week reporting no power and back fire. I drove it and it ran fine for a while, then all of a sudden it started running horribly, backfiring, etc.... When it starts to run bad, The Bank 1 Sensor 1 o2 sensor shows about 46Mv and sticks there. At the same time the ST Fuel trim for bank 1 spikes to 52%. Bank 2 remains normal and LT always remains at 0 (maybe part of the tune, we outsourced the tune). I did try putting an o2 in with no difference. After the van sit's, It will run good again for a while until it decides to act up again.

@ScannerDanner 8 жыл бұрын

sounds like a fuel starvation issue. Classic to have an intake backfire from lack of fuel. Fuel pressure test would be 1st order of business

@ReedsAuto 8 жыл бұрын

Thank you for the reply. Fuel Pressure holds steady at 60 PSI. Also it only appears to be affecting bank 1. Bank 2 functions normally. Fuel trim is normal and the o2 is switching properly.

@rexluongo6470 2 жыл бұрын

Is there any other things besides vacuum, maf, and fuel pressure that could cause both lean codes? Like valves, other sensors etc. Also, if the fuel tank is not venting could the tank build up a slight vacuum and cause low fuel pressure on a system with a purge valve that creates vacuum a tank that is not properly venting?

@ScannerDanner 2 жыл бұрын

Plugged injectors, severe misfiring (false lean), exhaust leaks upstream of the O2 (false lean) I'm sure there are more

@pk6336158 5 жыл бұрын

I got a question, if the o2 sensor is bad and make your long tirm fuel trim go -21%, i know the short term won`t be used because the o2 sensor will have to heat up but would the long trim be used on cold start up ?

@tonypond8196 6 жыл бұрын

hi help! short term fuel trim -30 at idle long term fixed 7.8 even with engine off no codes car runs ok but hunting at idle

@ScannerDanner 6 жыл бұрын

you have a rich condition, check your fuel psi regulator (if it is a vacuum type), check your fuel pressure itself and also your MAF sensor, there are other causes of this too. Check my chapter 4 and 5 playlist for more on this

@5riverz365 8 жыл бұрын

I have a 2001 bmw 330ci its throwing misfire codes and running lean. Bmw specific codes. P0300 multiple cyl random mis P1345 cyl 2 with fuel cut off P1350 cyl 5 mis during start Sometimes it throws a code for cyl 1 And it was throwing p0171 p0174 but now just misfire codes but stft r at 25% both banks and they lower when i raise rpm. Cant find any vacuum leaks with smoke or water. Thermostat seems to be stuck open cuz i got a code for that once. And coolant temp goes up to 181F when factory spec is 203F i think. I don't know if the fuel trims would be positive or negative with engine running cold with thermostat stuck open. Took it to someone and asked some other people. People around here seem to wanna throw parts at it than diagnose it.

@5riverz365 8 жыл бұрын

The car enters cl and then enters ol fault if u let it idle. So either i have to keep the revs high a lil to keep it in cl or i have to restart the car once it goes into ol fault to get it back to cl. Dont know how does that work

@lifeInProgress_8020 12 жыл бұрын

also I really enjoy watching your video. I try to get some of our younger know it all techs to watch your video. but you how these kids are, you just can't teach teach them any thing these days. So when they misdaig. some of use my sure everyone in the shop knowns.

@taurus2001dohc 8 жыл бұрын

Good stuff.

@dougjones4987 6 жыл бұрын

Good job

@ScannerDanner 6 жыл бұрын

Thank you!

@steveguest8028 7 жыл бұрын

Hi Paul,how long does it normally take ltft to update ?....ive got a vauxhall on which the stft changes instantly but the ltft seems fixed ?....Many thanks Steve

@bboyaddicted 11 жыл бұрын

Ive been having this problem that I can't figure out, at Idle my Long term fuel trim is around 8%, Ive been told anything under 10% is still relatively ok so Im not too worried about that the problem is that as I put a load on the car and accelerate, the Long term fuel trim gradually gets worse, (above 25%) until I get to WOT then it drops down to 4% and at half throttle acceleration the engine power surges...would these numbers point me in the direction of fuel delivery problems?

@rexmorgan72 9 жыл бұрын

So I have a 2006 Chevy Silverado 2500 HD, with 6.0 liter engine. I cannot seem to figure out why I am getting a p0171 and p0174 code. Looking at the STFT data at idle it shows values around -1, while the LTFT data at idle shows a steady +25. Increasing the RPMs to ~2000 or so gives me a STFT value range of ~+5 or so, while the LTFT data does not change from a value of +25. Any ideas about what might be the issue? Things that I have tried so far: Change air filter, change knock sensors (different issue), replaced the intake gaskets while changing knock sensors, replaced MAF sensor (although to me nothing looked to be wrong with the other one).

@ASEMasterTech909 Жыл бұрын

Paul have you ever had a truck 2003 Ford F150, 4.6 with Lean Bank 1, Rich Bank 2?

@ScannerDanner Жыл бұрын

I've seen a restricted cat on one side do that. Also a jumped timing chain can do the same

8 жыл бұрын

Hey! Do you know the common problem for the P0170 (Fuel trim bank 1) code? I changed my O2 bank1 (astra h belgium '07) and deleted the code but it appear again over 4 days. I saw my mechanical´s scanner and the voltage, before the O2 change, was too high with almost no variation.

@rraffx4829 4 жыл бұрын

If I receive this data only on bank one should I still pinpoint my issue to any type of vacuum leak? Anything else?

@ScannerDanner 4 жыл бұрын

what are you working on? some systems only have one bank for control

@E85_STI 7 ай бұрын

Hey Brother so it’s intermittent and it’s when the car sits at idle for a while but I get a lean code 0171 and I smoked it and no leaks or hoses other than smoke coming out the EGR and I was monitoring fuel trims and I sprayed it with brake cleaner and the trims went to 0. While idle the STFT is 14% and when I rev it or drive it the value goes down go 8 or less so my question is should the egr be normally open with the car off or could it be partially stuck and causing the intermittent code? It’s a 2008 Acura TL Type S

@ScannerDanner 7 ай бұрын

How many miles on that EGR valve? The stem of that EGR pintle will wear into the body of the EGR and cause a vacuum leak. I've had a 10% improvement on fuel trim numbers when changing the EGR valve that has a leaking pintle stem/rod/shaft whatever you want to call it. But they've all been on Fords

@E85_STI 7 ай бұрын

@@ScannerDanner I’m more than sure it’s the oem one and the cars at 185k miles. I sprayed soapy solution and I see the bubbles forming so the odd thing is there’s no hard starts or anything. I have a blue driver pro dongle and use that to monitor live data but I don’t have anything like you do with bidirectional abilities so I’m using the entry level since I just fix my own stuff at home .

@1130brent 7 ай бұрын

Hi Paul, you commented about a possible maf and I commented about the ltft being at 10 at idle and going up to 30 at 2k rpms. You pointed me to a different video of yours but now your comment and mine seem to have disappeared. I’m a little confused where they went but could you link me to that mass airflow video or tell me the name of it again?

@1130brent 7 ай бұрын

By the way I put a new hitachi mass air flow sensor on it and it didn’t fix it. I agree that maf makes perfect sense though. What are the odds I got a bad maf sensor?

@ScannerDanner 7 ай бұрын

Check your fuel pressure next before revisiting the MAF

@Monsterx13 9 күн бұрын

man i have a 2005 bucik with a lt 5.3 and i have already smoked it and checked fuel pressure and fuel pressure when driving and the car leans out at 24 percent only when driving i can’t figure out what it is am out of ideas already replaced 4 o2 sensors

@ScannerDanner 8 күн бұрын

What is fuel pressure under load? How does it run with the MAF sensor unplugged?

@Monsterx13 8 күн бұрын

@@ScannerDanner consist at around 59 under load and at idle no change in fuel pressure i have only cleaned the maf have not drove it with it unplugged because the trims are at 0 at idle most of the time

@JoelAutomotiveInaction 10 жыл бұрын

Paul next week I am taking L1 test reviewing fuel trim on a training program came this question : A technician is checking the scan data on the composite vehicle. The brake booster just replaced to repair a vacuum leak. The data shows the long term fuel trim at +30 and short term at -10. Technician A says this is normal. Technician B says further diagnosis is necessary. Who is right? Select one: a. Technician A b. Technician B c. Both d. Neither what is total fuel trim correction normal window?? I was working on 00 silverado 4.3 and I saw long term about 15% and stft close to 0. at different speed and load. while other vehicle example toyota they are stft 8 and ltft 10 or so. thanks master.

@ScannerDanner 10 жыл бұрын

Tech B is correct. Once fuel trim balances out you will have a LTFT of + 20% Total fuel trim should be -/+ 10 % Total fuel trim at any point in time is LTFT plus STFT and trouble codes will usually show up around 17 to 18% total fuel trim on most cars that I've worked on.

@JoelAutomotiveInaction 10 жыл бұрын

ScannerDanner thank you

@simonflores3410 9 жыл бұрын

ScannerDanner using a mt25000 snapon scanner on a 94 chey trk. 5.7 showing a lean condition and a fix # of 456 integrated 128 and Lt126 where do I start from here

@ScannerDanner 9 жыл бұрын

Further diagnosis is necessary. 10% is considered min/max normal range

@ScannerDanner 9 жыл бұрын

Sorry I guess I already answered this

@1130brent 7 ай бұрын

I tried this. 2011 Malibu 2.4 ecotec. P0171 dtc. My freeze frame ltft didn’t change with rpm’s. What might that mean from a scanner pov? It’s staying right around 20-30

@1130brent 7 ай бұрын

I’m a fan of your videos and your forum. Your instruction is first rate. I forgot to mention something I found odd. I have a lean code but am obviously running rich because; The plugs were carbon fouled, o2 voltage is .81. Is that just computer over compensation? I have no other code than p0171 either stored or current.

@ScannerDanner 7 ай бұрын

If O2 voltage is fixed at .8, that is a rich signal, but doesn't mean the O2 is reporting accurately. O2 sensor functional tests should be step 1. Force rich and lean conditions and watch the signal

@rodolfoaguirre4103 Жыл бұрын

Danner if there was no improvement when I creasing the rpm. What does that mean?

@ScannerDanner Жыл бұрын

then it is most likely NOT a vacuum leak. Fuel pressure and MAF sensor testing should be next on your list

@rodolfoaguirre4103 Жыл бұрын

@@ScannerDanner I test my Camry today and I got freeze frame data of RPM 642 Engine Temp 205 STFT 24.2 LTFT 25.0 TOTAL 59.2 TODAY I tested it and used live data and at idle 715 rpm Engine Temp 192 STFT -3.9 LTFT 1.6 1500RPMS. 2000RPMS. 200°F. 200°F STFT -1.6. STFT +1.6 LTFT -1.6. LTFT -1.6 2500 RPMS 203°F STFT 1.6 LTFT -1.6 DID I MAKE A MISTAKE SOMEWERE

@Frostedfk 3 жыл бұрын

Any clue to what the issue could be if my f150 is running fine without a/c but once a/c is on the LTFT fuel trim jumps to 25% bank 1 21% bank 2 at 2k drops to 10% on each side. Tried a smoke test couldn't find any leaks

@ScannerDanner 3 жыл бұрын

Trims are normal with the AC off?

@Frostedfk 3 жыл бұрын

@@ScannerDanner disregard my last 😅 fuel trims are high all around. 90% sure I dont have a vacuum leak.

@sauceman8710 8 ай бұрын

Can some one help me I got a 2010 Chevy camero 3.6.and the computer is reading Lt fuel trim b1 -17, and Lt fuel trim B2 -7

@ScannerDanner 8 ай бұрын

Negative trims means the engine has corrected for a rich condition. There are a list of things that can cause that. Fuel pressure too high Leaking injectors MAF out of calibration Incorrect calculations of alcohol (flex fuel engines) Stuck open EVAP purge valve (until the canister is depleted of fuel) Fuel contaminated oil O2 sensor issues Timing chain jumped Head gasket leaking (contaminates the O2s)

@JB-zn1kx 2 жыл бұрын

my p0171 was a clogged fuel sock and regulator

@servicewriter2905 4 жыл бұрын

Hi Dan. Quick question. On this test you demonstrate a quick test to see what type of lean condition this is by raising the idle to 2100.But what happens if you raise the idle to 2100rpm and LTFT drop near zero and STFT raise to positive 19? At idle LTFT is +19 and STFT 0.

@ScannerDanner 4 жыл бұрын

First, this means the memory isn't there for the higher RPM, no big deal, treat it the same way. Total trim was the same. Now hold it at 3500 RPM and tell me what total trim is (ST+LT)

@servicewriter2905 4 жыл бұрын

Hi Dan. Sorry for the late response. Hers is some data I collected a normal operating temperature. 800RPM = STFT(-2 to 2) LTFT(21). 2000RPM = STFT(-2 to 2) LTFT(13). 3000RPM = STFT(-4 to 4) LTFT(6) and last 3500RPM = STFT(-1 to 7) LTFT(6). FYI MAF, Plugs, Wires and a smoke test which by the way not leaks detected. Everything is OE. My head hurts just writing since its been a nightmare lol. Hope you can help.

@servicewriter2905 4 жыл бұрын

Hi Dan. Hey disregard the comment above. Upon further investigation. I noticed with battery terminals touched together I can reset the RAM memory. Upon doing that my fuel trims change. Still dont understand whats going on but here is the new data. At normal operating temperature, at idle, STFT fluctuates (14-26) and LTFT is at 0. But the moment I snap the throttle to wide open and the release it, once the rpms come back to idle the engine starts to run really rough and at the same time STFT goes to +33 and LTFT starts to rise to positive in order to smooth the engine out. Once engine gets back to running smooth at idle the STFT is now at (-3 to 3) and LTFT is at (17). The LTFT will ONLY get higher if I snap the throttle and the engine runs rough at idle(this is when LTFT starts to correct meaning get higher in positve number). Any ideas? Thanks a bunch.

@servicewriter2905 4 жыл бұрын

Oh and one more thing. Once the LTFT go up they will not go down unless I hold the rpms to like 2000 but other than that it will stay at 17. Its like if it learn that pid.

@ScannerDanner 4 жыл бұрын

@@servicewriter2905 these trim numbers are an example of a classic vacuum leak (trim numbers improve at higher RPM)

@sk8n854 9 ай бұрын

What about if it's only on bank 1 on a v8 mustang? Just a p0171 and the fuel trim is close to perfect on bank 2. And the trim on bank 1 gets worse when revved. I cant find anything wrong with the car. No vaccum leaks. Runs strong. I'm beginning to think maybe its just the o2 sensor. Already cleaned the maf sensor. The car has fairly new ford racing fuel injectors. I doubt theyre the problem either. Fairly new fuel filter as well. 150k miles. Wouldnt a failing fuel pump cause bank 2 to be lean as well?

@ScannerDanner 9 ай бұрын

I'd do an injector balance test next. It is possible the flow rate on one or more of the injectors is low. Do you have any misfiring symptoms? Roughness at idle? Is this an overhead cam engine? I've seen timing belts off one tooth do something similar too.

@ScannerDanner 9 ай бұрын

I just reread your post "fairly new Ford racing injectors"....where did you buy these? Could be subpar parts. If you don't have a way to do an injector balance test (i have videos on this) and if it's not hard to do, swap the injectors from bank to bank and see if your trim issues follow

@sk8n854 9 ай бұрын

@ScannerDanner no, problems really other than the check engine light and the trim level being off. Seems to be driving fine. The injectors came from American Muscle. They're the same spec as stock, and I wouldn't suspect them to be selling knock offs. Theyve only been on the car for maybe a year max, but that was also my next idea, as well, to switch banks with the injectors. It's just a bit of work, and I figured I'd ask around first before I actually did it. Thanks.

@sk8n854 9 ай бұрын

@@ScannerDanner oh sorry. They were Ford Performance. 24lb EV6 high flow fuel injectors from American Muscle. Idk why I said Ford Racing. Oh.. and yes. It's a 4.6L dual overhead cam engine.

@ScannerDanner 9 ай бұрын

@@sk8n854 our industry is plagued with shit parts these days

@DerekLMartin 12 жыл бұрын

What smoke machine are you using?

@dustinfrazier2505 3 жыл бұрын

Why would fuel trim numbers only be normal as soon as I let off the throttle . Then goes back lean at idle and higher rpm. By the way I'm from wheeling wv area not far from you in Pittsburgh. Just thought that was cool you not far from me. Wish I knew exactly where your shop is

@ScannerDanner 3 жыл бұрын

Bethel Park Pa my friend. My brother shop is Danner's Automotive 412-835-7530

@rondoschiavoni8840 5 жыл бұрын

Can a fuel trim be mechanically adjusted on a Buick 2003 3800 V6 engine?

@ScannerDanner 5 жыл бұрын

No, fuel trim is a computer strategy used to maintain good tailpipe emissions and fuel economy

@glycosaminoglycan 9 жыл бұрын

If the STFT numbers stay close to zero at all rpm ranges, it means the PCM is managing the stoich ratio properly, correct? So if this car you are diagnosing in the video just displayed high fuel trims on both banks, but the STFT numbers looked great at all rpm's, would it mean that the lean condition was fixed and it would take many drive cycles for the LTFT numbers to come down to meet the STFT numbers clearing the lean codes? I understand the LTFT is learned over time, so is it learning from what the STFT's are doing even though the STFT' are not stored, but the LTFT's are? Thanks Paul!

@glycosaminoglycan 9 жыл бұрын

+glycosaminoglycan - My STFT in Park with the engine idling fluctuate between +3 & +5. At 1500rpm -2000rpm they hover around 0 and at 2500rpm the STFT go slightly negative -4 to -7. If the transmission is engaged in R or D, the STFT numbers go from +5 to +11/12/13 Upon acceleration from idle to 2000rpm, the STFT run into the +20's maxing out. After watching all of your videos on fuel trims and applying the principles, I thought I fixed my lean condition which was from a inoperable fuel injector. All of my misfire codes went away. I'm only getting one DTC. P1178 - Maximum Positive Adaptive Air Mass Flow Rate Correction Fault The engine has 2 banks and the fuel trims look very similar on both sides as do the front O2 switching. Both downstream 02's are reading lean. I'm going to flood the intake with propane while the transmission is engaged to see if those numbers come down. Any other idea's? Thank's Paul!

@ScannerDanner 9 жыл бұрын

+glycosaminoglycan copy and paste these questions to my forum. thanks! www.scannerdanner.com/forum#/general-repair-questions/

@consaka1 8 жыл бұрын

+glycosaminoglycan I'd be interested in knowing what year and type of car that is. Have you done a vac leak test? possibly a smoke test?

@glycosaminoglycan 8 жыл бұрын

1997 Range Rover 4.6 HSE Tested everything. I mean X's 3! For months I thought one or two of the cam lobes were worn and the ECU was compensating for this which adversely disrupted the stoich on the other properly working cylinders. I had an ASE certified mechanic look at. After 6 hours of diagnosing it, he couldn't figure it out. Said it was running a little rich at idle, O2 sensors functioning correctly, but everything was within specification. He suggested the ECU was the problem. However, I was able to get my STFT's down around zero after correcting a fuel delivery/restriction/pressure problem. I'm still getting O2 codes on both banks popping up every once in awhile which is what I originally went to have diagnosed instead of just replacing them hoping to fix the problem (after I switched the front pair with the post-cat rear O2 sensors) instead of replacing them. The only complaint I have as of now, is from time to time, I notice sluggish acceleration up to 30 mph if the engine is not at operating temperature. Once I get to 30-35 mph, then it really moves after that and the fuel trims hug 0 nicely. What would cause a rather low-end high torque motor to exhibit sluggish low rpm power and then really open up at higher cruising speeds? (On acceleration, I rarely need the RPM's to exceed 2000 on the tach through all the gear shifts to achieve the desired speed, it just feels weak on low speed accleration rather than high speed acceleration) Thanks Consaka!

@consaka1 8 жыл бұрын

glycosaminoglycan hmm that's interesting. One thing that pops to mind based on experience is that O2 sensors start degrading the day they go into service. I have fixed engines with supposedly good O2 sensors by replacing those sensors. If they are more than a year old I would replace them with good quality ones even if they are a bit more spendy. The good ones last a lot longer then some of the cheap ones. I have seen cheap ones last less than a year and some never work quite right for touchy engines. (cant rem the engine now buuuut.) Than would start looking at other things like injector spray patterns. After all that I would watch the live data while someone else drove through the sluggish part. Sounds to me like the sluggish could be a lean condition. Slightly lean can run without missing but just not have the power. There is a reason why fuel systems dump fuel rich under hard acceleration. I have seen some engines even have a separate injector for cold start/run situations. I think that was the volvo I had. Carbs had accelerator pumps and chokes to give extra fuel when cold. If you are sluggish till you warm up you might check your temp sensor for the engine computer. not to be confused with the one for the dash instruments if they are different as they often are. Check the sensor and then check the wiring from the sensor. Double check that sensor actually has a ground. I have seen some pipe thread sensors isolated from ground by good old teflon tape used for sealing. I like tape better than the goop but too much can be no good. So there are my ideas. Hope some of them are helpful

@Element_lifestyle 2 жыл бұрын

👍👍👍

@dimisrambodimisrambo7285 9 ай бұрын

when we have a lean situation at all rpm but the o2 sensor shows correctly that the stft shows a lean mixture? can a bad ecm create such a problem? are the stft only controlled by the o2 sensor?

@ScannerDanner 9 ай бұрын

Step 1, confirm the oxygen sensor can respond to a rich condition.

@dimisrambodimisrambo7285 9 ай бұрын

@@ScannerDanner i did it everything is new o2 maf f pumb injector timing is ok!!!! that's why i asked about the ecm. is there something that the f trims would see but not the o2 sensors?

@ScannerDanner 9 ай бұрын

@@dimisrambodimisrambo7285 new means nothing!

@dimisrambodimisrambo7285 9 ай бұрын

@@ScannerDanner of course I learned this from you and I have certainly checked all the above fuel pressure fuel delivery clogged exhaust air leaks timing leak cylinder test 18 in/hg at idle int.man.pressure fluctuating o2 sensor 0,1 -0.9 v maf new oem everything is fine. I reset the f trims and as soon as the car starts the stft jumps up +15% no fault code the only problem is a slightly unstable idle which is corrected immediately when the lpg comes in !!!!!!

@ScannerDanner 9 ай бұрын

@@dimisrambodimisrambo7285 okay, what are trim numbers at idle compared to 2500 rpm in park?

@CryptoJunkie 4 жыл бұрын

Great video. Easy to follow. But what if I have these codes at 62% load & 65mph with RPM 2000? LONGFT1 & LONGFT2 = 25%. I cleared codes and got it again at 68% load & 6mph with 1500rpm. LONGFT1 & LONGFT2 = 34% I watched your MAF case study and I put a new MAF but codes came back. I don't know what's up.. Thanks

@ScannerDanner 4 жыл бұрын

check your fuel pressure next, it could be dropping under load

@TheDrewker 5 жыл бұрын

Every video on fuel trim seems to be a low idle lean/vacuum leak situation lol. I have the opposite, STFT is perfect at idle, shoots up under load, loses power and hesitates. Cant find any videos that focus on high rpm lean

@ScannerDanner 5 жыл бұрын

I have a ton of those :-) Your top two causes of that is low fuel pressure (dropping under load) and a dirty or contaminated MAF sensor. Look under my Chapter 16 playlist for fuel pressure issues and under my Chapter 12 playlist for MAF issues.

@TheDrewker 5 жыл бұрын

@@ScannerDanner Thank you! I did end up finding one of your videos on the MAF (Troubleshooting P0171 & 174 trouble codes/how to read & interpret fuel trim data)- cleaning that is the first thing I'm going to do today. I also have to do the P0449 EVAP solenoid (because '06 Silverado 5.3L), I found one of your videos on that and a couple other people. I know it can cause trouble starting (which I'm experiencing 3 tries fo cold starts), could it also be causing low fuel pressure under load? Or am I Your videos are highly informative and easy to follow. Makes sense you're an educator! Feeling pretty confident I can sort out what's going on and save myself a lot of bills. I'll do your premium sub for awhile to say thanks once I've nailed it down.

@perez7667 4 жыл бұрын

Can't you use injector pulse width to determine an injector misfire on a single bank by comparing both bank injector pulses, knowing that with a stuck open injector the pcm will reduce injection pulse and with a stuck closed injector the pcm will increase injector pulse? Stay safe and keep your mom as safe as possible.

@ScannerDanner 4 жыл бұрын

fuel trim is my preference

@perez7667 4 жыл бұрын

I was just trying to see your point of view. If it is something that I can go by. I, myself, go by by the fuel trim as well. That's why I love your video titled" Using fuel trim to identify types of misfire, can it be done?

@bboyaddicted 11 жыл бұрын

it doesn't throw codes either so I have nothing to lead me in the right direction

@samuramex1980 7 жыл бұрын

Did you fix it ?

@mikeculver8970 7 жыл бұрын

ok what if your stft is close to 0 at idle but increases a little as you increase rpm till you get to about 1500 rpm then it jumps to 19.5% then when you hit about 2300 rpm it go's back down to about 0 ltft varies from 11 to 39%

@ScannerDanner 7 жыл бұрын

It is becoming more and more difficult to answer questions here. I have 80,000 people asking me for help now. So I have created a forum to help you guys better. It is free to join and we can exchange pictures, wiring diagrams and waveforms if needed to help guide you through the process of troubleshooting your vehicle. Thank you so much! Hope to see you there. Paul Danner (ScannerDanner) www.scannerdanner.com/forum/post-your-repair-questions-here.html

@josesanchez-bc3ve 2 ай бұрын

What about if LTFT is staying in 0% and STFT is going from 0% to - to + all crazy

@ScannerDanner 2 ай бұрын

ST should be bouncing around as it is controlling inj pw and in turn O2 signals

@josesanchez-bc3ve Ай бұрын

Oh ok

@mrthomson5582 8 жыл бұрын

can you tell me about negative numbers in long term fuel trim please?

@ScannerDanner 8 жыл бұрын

+Mr THOMSON kzfaq.info/get/bejne/pbiIZblnxMeXlJc.html

@ScannerDanner 8 жыл бұрын

+Mr THOMSON it means your engine is running rich

@THERIGGEDONE 8 жыл бұрын

Would it be a fuel delivery if STFT goes up in the 30% range while the LTFT goes to 0 while increasing RPM? thx

@ScannerDanner 8 жыл бұрын

+THERIGGEDONE I do not concern myself with fuel trim while changing throttle angle or accelerating. Only steady throttle.

@sandygrungerson1177 6 жыл бұрын

that might be a point to emphasize, SD

@jasonwoody8041 6 жыл бұрын

I have p0174 and p0174 on my 2000 gmc sierra 7.4l vortec. I'm at my wits end and might except defeat and take my truck to the dealer for the first time... but before i do can you give me a option or two to look at? My issues are random but under moderate load the motor falls on its face and has like 1/3 the power it should. Truck dont seam to care if its up to temp or stone cold. But it does only happen one time per driving session and it happens almost right away from start up. Fuel pressure falls in spec (55psi key on engine off and 60psi key on engine on. Gauge wont drop a psi with a hard snap off the throttle up to the limiter. But i have replaced the pump, filter, regulator and cleaned the maf sensor. Motor runs smooth and only has the issue under load. Even then it's smooth just no power..

@ScannerDanner 6 жыл бұрын

Unplug your MAF and test drive it. If it runs good, your MAF is the issue. If it runs the same, we go in another direction.

@jasonwoody8041 6 жыл бұрын

ScannerDanner dies instantly with the maf unplugged

@ScannerDanner 6 жыл бұрын

It will initially, start it up again and keep your foot on the gas pedal to keep it running for a minute. It should then recover and allow you to drive it. It may stall when coming to a stop, but we don't care about that. We just want to know if your power is back.