You are correct. LTFT does not react that fast, but what you are looking at is learned fuel trim numbers in different cells. Remember that LTFT has a different learned value for every load and RPM combination. It is not just one flat adjustment across the board.

Awesome videos. You make fixing my car look like fun! You've really helped me out. Been chasing a rough idle on my Aviator for weeks. Thought for sure it was a bad O2 sensor. Used your videos and a scanner software to verify that they are actually all working correctly. Actually looks like I have a vacuum leak. Long term fuel trim is high (10-20%) but goes normal at 2500RPM and then short term goes high. Not having luck finding the leak, but I haven't given up yet.

Good question. Most MAF engines will idle lower than normal with a vacuum leak. It is the speed density (MAP) engines that will idle high with a vacuum leak.

@trublue2319

3 жыл бұрын

Thank for the info have learned alot from you

great vids.. really enjoying watching and learning new techniques.. keep em coming... liked and subbed

Every car reacts a little differently, especially a car with a MAP sensor. The MAP will sense the pressure change from the vacuum leak a send a higher volt signal to the PCM. The PCM will in turn open the injectors more which will possibly mask the vacuum leak/lean condition.

Thanks for your quick response, really appreciate it helps alot ..KEEP IT UP

Awesome hands on Explanation! Thank You!

@oldschool454

9 жыл бұрын

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Thanks Paul. I was thinking IATs shouldn't matter very much, especially on a MAF system. I think it's possible that I have some kind of intermittent issue causing my trims to creep up. Like today at idle the LTs were 3.8 and 1 or 2% for the STs. Good call on the gas, we have some funky gas out here in CA. That's a great point. I will see if I can figure this out or not. Keep up the great work - I love your videos.

ambient temp. is monitored by the PCM typically by using the IAT sensor input. So you are correct in that hot air is less dense but this factor is not compensated for using the fuel trim. The entire fuel curve is adjusted based on the IAT signal (it is a small amount though).

I am seeing -7% STFT and -8% LTFT that go to ~0% with acceleration. Any clue what this could indicate? I am also having rough idle and hesitation. Thanks

Great video

LOL the engine is on fire!!!!! :) Sorry about not mentioning what I was doing. I tried to shorten the video to mainly focus on the fuel trim numbers and how to use them.

Good stuff Thanks !!

Excellent.

Your videos are by far the best on KZread! Quick question if you have time... P0171 on LS1 engine 187K miles- no drivability issues, no evidence of vacuum leaks could be found. no misfire or other codes. STFT bank1 seems fairly normal yet LTFT in bank 1 is highly erratic- from 15 to 25 and never stays steady. The LTFT almost looks like a STFT trace in fact. Bank 2 looks rock solid with tight STFT and LTFT right at zero. I'm thinking injector partial clog but don't have pulse tester. Ideas?

It depends on the severity of the vacuum leak. If it is severe enough you would also see the STFT in the positive range but only after the LTFT has reached its maximum. In this case the LTFT was able to bring the STFT into a normal range of near 0%. Also for your second comment, a dirty MAF would show fuel trim % increasing with an RPM rise NOT decreasing.

Hey Paul, Had a few fuel trim related problems over the past few days. Today had a -24 LTFT one where the valve timing was a tooth out on the exhaust cam. The LTFT returned to zero @approx 3000rpm. Also had a few air leaks on another car, what smoke machine do you use? been looking at the smoke pro approx £600-800 in the uk depending on model.. keep up the hard work!

thanks for comment and i promise you will not be disappointed in my eBook

thanks danner

your videos are great just picked up the snap on souls ultra do you figure this is a good scan tool?

How about a dirty MAF sensor? Did you check it? I have a video on a toyota with a dirty MAF.

Anyway 11-12 % is a little high for your trim numbers. It could be a small vacuum leak or possibly restricted injectors (like in my last video on the Pontiac vibe). It could be other things too. Another thought is the alcohol % in the fuel. I'm not sure what you guys do in California but if they are mixing in more alcohol in the fuel this will also drive your fuel trim numbers positive.

Hey Paul Are you smoking the air induction or the engine is on fire?:):) Another Ford intake leak.Very unusual for Ford Explorer.You must love STFT and LTFT ,because half of your uploads are about Ford fuel trims.LOL Thank you for another awesome video

what do you think about the cigar trick to find vacuum leaks? ..blowing the smoke up the air intake pipe

Excellent Diagnostic as always , so my understanding that each time trouble code P01000 pops up thats mean previous code has been cleared without fix the issue ?? thanks again

I like you teacher

Well i replaced the intake and TB gaskets since they are cheap. I also used a homemade smoke machine and there are definitely no vacuum leaks. I'm not sure why the ambient temp affects this, but now LTs are +14/15 and sometimes the total correction will get close to 20%. I suspect a fuel system issue or injector problem now.

finally after taking off the intake manifold and pulling valve covers to check cam chan tension. it got worse and was pinging. The cause was the Mass air flow sensor, was reading airflow fine but frequency was showing i was at 4000 to 5000 ft elevation not under 1000 where i am. would you like my old sensor to use as a case study?

You guys should try replacing timing chains on one fo thes 4.0l SOHC's its a treat!

Ford EGR valves always show a leak when smoke testing.

where at on the egr valve was it leaking? i see them leak in the diaphragm area when it had lean codes, but theres a ford service bulletin the says its normal to see smoke leaking from the egr valve, iac valve, and imrc, and not to replace them, but i dont know what to believe

It is possible you could have an injector problem. You need to get one of those timer tools :-) Also check the O2 sensor itself, it could be going bad as well.

Hi Paul I noticed that the actual idle rpm is lower than desired .But with vacuum leak,should it be higher rpm ?or pcm compensate by adjusting the throttle? Thank you

I have a big question. Loose or tight Valve clearance can cause positive fuel trim numbers?

i have long term fuel trims of 7 percent and 9 positive one bank being more and this is at idle. is this a concern being this percent of trim. and there is a slight rough idle. i do suspect a coil pack not fiting all the time. i installed a known good coil pack in the suspect bad one and 0 percent misfire shows on mode 6 test. but still the same fuel trims

Bello Danner, I have a question. It could be wrong but I connected my Android phone to my colleague VW and it showed long fuel trim at -6. The car was cold so... It is normal?

Hi Paul, trying to troubleshoot a periodic P0170/P0173 on a 2000 ML320. Negative LTFT is the cause, freeze frame shows -15 or so when the code sets. Doing research on negative LTFT seems to point to only a few things, leaking injector or stuck open pintle. Since it is both banks I am having my doubts. Could it also be a bad MAF, but usually a bad MAF would result in highly positive LTFT. (unless this faulty maf is telling the ECU *more* air is entering than there really is?)

Now have you ever noticed fuel trims going more positive if it's really hot outside? I have a 2000 Toyota Echo, and it seems like the LTs like to hang around 6 or 7 for most part but now it's starting to get really hot out here in CA and I noticed them hanging around 11 or 12 the other day. I would think they would want to go negative since hot air is less dense than cold air. Who knows, maybe there is a small vacuum leak manifesting. Car runs pretty good though.

Hi Paul how about when you car have both MAF and MAP sensor? for example I have a honda accord 05 which contain both sensor..I have an issue like this where at Idle my trims are leans but at load is perfect almost at 1.00 plus from time to time I get the lean condition code P0171, on the process of finding the issue I did find one small vacuum hose disconnected but my idle was never affected by this. Car always Idle like there was no issue.

I wish there were more speed density with map sensor only videos. Seems most videos are like this-higher rpms, fuel trims lower. Does nobody work on speed density engines.

I wouldn't be too concerned with these numbers but it does suggest possibly a small vacuum leak.

Will a vac leak on a MAP engine cause a low idle?

In a lean condition, there will always be a vacuum leak somewhere in the engine?

No, there are many causes of a lean condition. Here are a few of them. Lower than normal fuel psi Vacuum leaks Clogged injectors or injectors not firing Contaminated fuel ECT or IAT sensor problems MAP/BARO or MAF sensor problems (especially a dirty hot-wire type MAF) Jumped timing chain/belt Exhaust leaks upstream of the O2 (false lean, causing rich a/f ratio) Severe misfiring (false lean, causing rich a/f ratio) AIR system problems (false lean, causing rich a/f ratio)

Paul, what should I look up to if at higher rpms it stays the same or gets worse? I'm having an 02 Explorer with a P1151 code in it and I did some troubleshooting but had to stop because I had to go to work. B2S1 O2 sensor was fixed lean. i made the mistake that I didn't check B2S2 to compare... I did react a little to carb cleaner and sometimes it will just act normal stoich....

@movingupautodiagnostics8645

7 жыл бұрын

Fuel trim was rich and suddenly normal at idle.

what if the leak gets worse?

No because the EGR was functional, it was just leaking vacuum around the pintle stem area. Common Ford problem.

i tried it. it sort of works. but the downside was i ended up throwing up. from puffing too much too fast.

P1000 is a Ford thing only and it means that the OBDII readiness monitors have not yet completed. Once all the monitors run the P1000 code will disappear. It is a red flag to the tech. working on the car that someone was just there.

if its bad enough of a leak then yes.

koer = fuel press. 58psi, rpm 865 ho2s b1s1= 0.10- 0.110 ma, ho2s b1s2= 0.01 , st 1.56%, lt 20.31%, maf 5g/s

I have a Mazda 6 2006 2.3 L I took the battery out to inspect my transmission mount because I had noticed that when I was switching gears it was making a noise in doing that I took out my battery I disconnect the negative battery terminal and also the positive terminal and remove the battery and the tray from the vehicle after inspecting I placed the battery back into the car and put the terminals back on it I took the car for a drive and noticed that all the sudden now there is rough idle there is stalling my RPMs and my speed metre seems a little off everything was perfectly fine with the car until I remove the battery I watched a couple videos telling me to let the car run for 20 minutes and then turn the cars air conditioning on cold and let it run for another 15 minutes and then take the car for a drive I did this and everything seem to work fine but before I did this I got this trouble code P0506 but now the light is off and has not come back on but I am having a problem again with stalling the car will just stall and turn off but the lights will stay on on the dash and I'm able to turn the vehicle back on and start it and drive again I don't understand what is wrong is there anything you here in this information I've given you that could lead you to help me any information would be greatly appreciated thank you kindly I really am thankful

@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

My issues are all on Bank2. With a live data scan going I ran it down the road and stopped at the stop sign. This was my readings st ftrim1 % 0.0 lt ftrun1 % -5.1 st ftrim2 % -50.6 lt ftrim2 % -39.7 Done a complete tune up cap, rotor, plugs wires and plugs. Not the cheap stuff (learned my lesson there) Replaced 2 o2 sensors also 1 was bank one and the other was bank 2. on was up and the other was down stream. I can crawl under and verify which they were. What ever the previous code were telling me to replace. When in park I can't seem to repeat the conditions. Only while driving. Any thoughts would be appreciated since I am a single father of 7 kids and this Suburban is my short bus.

@nicholas8479

6 жыл бұрын

Mr Berserker My guess is a leaky injector on bank 2. Was that it?

I'm sorry I don't get it.. Long term fuel trims don't react that fast I don't get it. If I simulate a vacuum leak on my mercedes the short would add fuel (like +15) but the long term won't be affected before AT LEAST 15 minutes to change one percent at a time! Is it a ford thing to have the long term change that fast?

if the LTFT and STFT numbers goes higher when you accelerate the engine what is the problem

@ScannerDanner

8 жыл бұрын

+Franc melendez this points toward a fuel delivery problem with the top two suspects being a dirty MAF sensor or low fuel pressure

I have a 2005 mazda rx8 , whit p0171 , I check for vacuum leaks whit a smoke machine ,cant find any leak, fuel trims are lt 25 st 0, I don't know what to do someone help!!!!!!!!

@ScannerDanner

8 жыл бұрын

+alekstolstoi next two things to look at is fuel pressure and see if the MAF sensor is dirty. I have videos on both of these. Would you like me to post a few links?

I now realize he is Paul, I was saying Dan due to the title of channel.🙄

@ScannerDanner

Жыл бұрын

🤣 you an everyone else Danner is my last name 😉

maybe it a ford thing... because on a Toyota if there is a vaccuum leak, the short would be high and it some case I have seen both Long and short at plus 20%. and when a MAF gets dirty on a Toyota, the long would be at plus 20 with short at 5%. then long would improve as you rise the rmp.

after higher rpm for motor , long term fuel trim is not improved what is now the problem

@ScannerDanner

6 жыл бұрын

it's not a vacuum leak. focus on fuel pressure and your MAF sensor next

@SA-qn9rg

6 жыл бұрын

thank you

someone help!!!!!!!!!!!!!!!!!!!!

I just don't get how more air and more fuel equals lower rpm.

@Ashroyer86

4 жыл бұрын

Or was it maxxed fuel trim and the air leak was still greater than the fuel compensation?

@ScannerDanner

4 жыл бұрын

Exactly! your second statement

Im dizzy. I don't know what happened✨

ok scanner danner this is what a got, freeze frame = st 25% , lt2.3%, baro press. 30.1 inhg, air flow rate 29.05g/s, rpm 3254...

Hello, excellent video! A little question, may be you can help me, what means this values?: At idle (LTFT +10% , STFT -4 ) At 2000 rpm (LTFT 0%, STFT 7%) At 3000 rpm (LTFT +4, STFT +4) My mileage is very bad!!

@ScannerDanner

8 жыл бұрын

+Juan Gabriel Florez Moreno basically normal, possibly a small vacuum leak

@juan64bits_

8 жыл бұрын

ScannerDanner thanks for your answer. I'm worried because the fuel trims are getting worse, same beavior but LTFT up to +14,8% and STFT up to -13,3%.

@ScannerDanner

8 жыл бұрын

+Juan Gabriel Florez Moreno okay. When you see numbers like you have, it means that whatever was causing your lean condition is now, not there. LT at +14 and ST at -13 equals a total trim of 1. Make sense? Some common causes of that, is an intake manifold gasket leak that improves with temp. Watch this video kzread.info/dash/bejne/ZYZ6trVrYtqcpLA.html

When I see him using the $12K Verus I think "He's got the Tricorder again. How do us poor peons do it?"

@death2peepz

Жыл бұрын

Take it to a shop

TBH I am tired of chasing codes and need electric vehicle prices to drop/become better/last longer. I'm fed up with this stuff.

@ScannerDanner

Жыл бұрын

You think your going to get away from this kind of stuff with electric cars? You won't my friend. We already deal with the same types of circuitry