This is the best way to walk through anyone that is learning or experinced to just test with scan tool correctly. I apperciate how professional and straight forward this video explained the fuel trims. Thank you!
thanks for breaking this down. ive been in the industry for 18 years and this is the best way ive seen this explained without overcomplicating it or putting you to sleep! ha
Nice video. Just wanted to add a comment for cars that use a MAP sensor instead of a MAF sensor. Vacuum leaks on MAP controlled vehicles will not be visible in the fuel trims.
There are two strategies to determine the amount of fuel to inject into a running engine. One is to measure the incoming air mass using a mass air flow meter, the other, also called speed density measures the pressure in the intake manifold. Both of these methods are effective at determining the air volume, hence the PCM knows in advance of the combustion event how much fuel to apply based on the measured air volume. The idea is the keep the air to fuel ratio at 14:1. When the measured air volume is accurate, and the fuel delivery is accurate, the theoretical fuel trims will be zero since the resulting combustion will not be rich or lean. The reason the fuel trims of speed density systems are not affected by a vacuum leak as shown in the video is because the instant the leak is created it is detected by the MAP sensor, the fuel is adapted to the leak immediately resulting in a 14:1 ratio, which is perfect and the fuel trims remain at zero, or no change. For engines that use a MAF, a vacuum leak as demonstrated in the video, means the additional air did not get measured, therefore the PCM does not know to increase the volume of fuel. The lean mixture is burned, and then the O2 sensor reports a lean condition, resulting in positive change in the fuel trim to correct the lean condition. Fuel trim is driven directly by the closed loop feedback from the oxygen sensor. Let us know if any of this makes sense, and just maybe Royal can make another video to elaborate more. Fuel trims are a very powerful diagnostic tool, and are also the most misunderstood.
Keep these videos coming . I want to build a solid foundation to diagnose issues . Getting data from the scan tool FIRST before loading the parts cannon . Knowing what to look for from each sensor and what the data is telling you . Thanks .
If I was going to teach a vacuum leak AKA false air leak, I would want to show MAF readings also with this very small leak and a larger leak since you were able to control the size so I could monitor MAF small leak and larger leak and after the repair and since I am teaching MAF I would also have waited for a problem in a vehicle with a dirty MAF then done cleaning after fixing the leak to show more MAF readings based on these 2 scenarios. This is why creating a problem is not always a real-world scenario but THANK YOU for this beginner lesson that is in fact a useful lesson for a vacuum leak ONLY on any car that you did mention.
Excellent video!! Automotive tech here, always searching for knowledge and this channel alone is gold when it comes to learning with you and employees. Great staff and clear and precise explanations you don't get often!! Love it!
This channel is awesome thank you so much Im trying to get into the diag side of auto repair and these vids are absolutely priceless gems. Simple, straightforward & practical.
P0171 fuel system lean can also be Maf and fuel system issues. Dirty fuel pump or injectors. Had one recently with dirty injectors and wondering why the LTFT wasn't dropping after the repairs. Now I know that I have to cycle the key off. Thanks.Always great diagnosing from you guys
He is referring to vacuum leak and the clue here is huge adjustment at idle. A weak pump, clogged injectors, faulty MAF sensor etc. will cause high fuel trim numbers as well, but they will be present at different load/rpm ranges.
Yeah for those failing parts the fuel trims will continue to go up (positive numbers rising ) as the load / demand for fuel (such as during increased RPM) is introduced in the diagnostic process .
very educational, you confirmed what I thought about vac leak after looking at trims like this. But how d I find? You touched on carb cleaner but I tried that before and found n o changes. I supposedly had a smoke test, but didn't watch and he 'didn't find anything,' but that was a P0171 issue a while ago, that was fixed. Intake gasket? Valve cover gasket? Similarly, you mention issue is only at idle, hence can I go on a road trip which will be mostly highway?
What would be the causes of fuel trim high under load ? And will fuel trim or should they differ under load and at idle or will they generally even out under load and idle ?
Thank you for the video! I got a Renault Duster with a vacuum leak suspicion. In idle, I got 15% STFT and 6% LTFT. However, at 2500 rpm, I got -10% STFT and the same 6% LTFT. Is it still a vacuum leak?
By "Up further" I'm thinking you're asking if it gets more negative or stays very negative. If not, let me know. If so, then It could be a fueling issue (fuel pressure low, partially restricted injectors) or it could be an intake air meter reading. That could be a Mass Air Flow Sensor problem. It is also possible that a temperature sensor is reading too hot but that would be rare and would probably set a code for temp sensor.
@@theroyaltyautoservice thanks for the reply! What are some things that could cause this? Vacuum leak or leaky fuel injector? Or maybe small boost leak?
This is the best way to walk through anyone that is learning or experinced to just test with scan tool correctly. I apperciate how professional and straight forward this video explained the fuel trims. Thank you!
thanks for breaking this down. ive been in the industry for 18 years and this is the best way ive seen this explained without overcomplicating it or putting you to sleep! ha
Thanks for finishing to the end to where the fuel trims normalized .
thank you for you time doing these videos
Sherwood, this is why I enjoy this channel. Excellent explanation using the ATS scan analyzer. Thanks
auto tech here! I'm the heavy line guy at the shop. not good at trouble codes diagnostics! this video is pretty informative. thanks a lot!
Air Conditioning would be a good video! I just barely scraped by passing the A7 and I certainly could use some reinforcement.
Nice video. Just wanted to add a comment for cars that use a MAP sensor instead of a MAF sensor. Vacuum leaks on MAP controlled vehicles will not be visible in the fuel trims.
Kindly explain why
Yes please.
There are two strategies to determine the amount of fuel to inject into a running engine.
One is to measure the incoming air mass using a mass air flow meter, the other, also called speed density measures the pressure in the intake manifold.
Both of these methods are effective at determining the air volume, hence the PCM knows in advance of the combustion event how much fuel to apply based on the measured air volume. The idea is the keep the air to fuel ratio at 14:1.
When the measured air volume is accurate, and the fuel delivery is accurate, the theoretical fuel trims will be zero since the resulting combustion will not be rich or lean.
The reason the fuel trims of speed density systems are not affected by a vacuum leak as shown in the video is because the instant the leak is created it is detected by the MAP sensor, the fuel is adapted to the leak immediately resulting in a 14:1 ratio, which is perfect and the fuel trims remain at zero, or no change.
For engines that use a MAF, a vacuum leak as demonstrated in the video, means the additional air did not get measured, therefore the PCM does not know to increase the volume of fuel. The lean mixture is burned, and then the O2 sensor reports a lean condition, resulting in positive change in the fuel trim to correct the lean condition.
Fuel trim is driven directly by the closed loop feedback from the oxygen sensor. Let us know if any of this makes sense, and just maybe Royal can make another video to elaborate more. Fuel trims are a very powerful diagnostic tool, and are also the most misunderstood.
Wow thanks man thats a great explanation
Good observation. Suspecting a vacuum leak you may look at load and map sensor pids, rpm , IAC counts if present, throttle position....
Excellent explanation for those that may be new to diagnostics!
Keep these videos coming . I want to build a solid foundation to diagnose issues . Getting data from the scan tool FIRST before loading the parts cannon . Knowing what to look for from each sensor and what the data is telling you . Thanks .
If I was going to teach a vacuum leak AKA false air leak, I would want to show MAF readings also with this very small leak and a larger leak since you were able to control the size so I could monitor MAF small leak and larger leak and after the repair and since I am teaching MAF I would also have waited for a problem in a vehicle with a dirty MAF then done cleaning after fixing the leak to show more MAF readings based on these 2 scenarios. This is why creating a problem is not always a real-world scenario but THANK YOU for this beginner lesson that is in fact a useful lesson for a vacuum leak ONLY on any car that you did mention.
Excellent. Your content is. Thank you for posting this stuff.
Excellent video!! Automotive tech here, always searching for knowledge and this channel alone is gold when it comes to learning with you and employees. Great staff and clear and precise explanations you don't get often!! Love it!
This channel is awesome thank you so much Im trying to get into the diag side of auto repair and these vids are absolutely priceless gems. Simple, straightforward & practical.
Another great video, thanks. Keep them coming!
I love your teaching approach. Very clear very plain and easy to understand. I’m glad I just found this channel. Great video, and a great information!
P0171 fuel system lean can also be Maf and fuel system issues. Dirty fuel pump or injectors. Had one recently with dirty injectors and wondering why the LTFT wasn't dropping after the repairs. Now I know that I have to cycle the key off. Thanks.Always great diagnosing from you guys
He is referring to vacuum leak and the clue here is huge adjustment at idle. A weak pump, clogged injectors, faulty MAF sensor etc. will cause high fuel trim numbers as well, but they will be present at different load/rpm ranges.
Yeah for those failing parts the fuel trims will continue to go up (positive numbers rising ) as the load / demand for fuel (such as during increased RPM) is introduced in the diagnostic process .
Excellent info. I always learn something from Sherwood. Thanks for clear & to-the-point instructions.
Awesome quick video!
Great video, Thanks Professor really appreciated😍
Stay Safe👍
👌Köszönöm Professzor!
great video thanks. good luck.
Great video
Great info, from a true pro! 👍
very educational, you confirmed what I thought about vac leak after looking at trims like this. But how d I find? You touched on carb cleaner but I tried that before and found n o changes. I supposedly had a smoke test, but didn't watch and he 'didn't find anything,' but that was a P0171 issue a while ago, that was fixed. Intake gasket? Valve cover gasket? Similarly, you mention issue is only at idle, hence can I go on a road trip which will be mostly highway?
Another great job. Thank you.
great video , keep up the great videos thanks
Great explanation!
Great, informative video! Keep them coming!
Awesome!!!
What would be the causes of fuel trim high under load ? And will fuel trim or should they differ under load and at idle or will they generally even out under load and idle ?
Thank you for the video! I got a Renault Duster with a vacuum leak suspicion. In idle, I got 15% STFT and 6% LTFT. However, at 2500 rpm, I got -10% STFT and the same 6% LTFT. Is it still a vacuum leak?
Sounds like it could be a vacuum leak going by those fuel trims. Adding 21% at idle but at 2500 total trim is 4% (which is good).
@theroyaltyautoservice Thank you, Sir, for your answer! Love your channel!
I’m also wondering really weak fuel pump or a bad oxygen sensor give you a vacuum leak
in my car bank 1 i solid around 2% on both FT, but bank 2 long trim is -8% and short around +1.5. Is it fuel injector issue?
What about exhaust leaks vs fuel trims?
👌🏻
👍👍👍👍
If you take the RPM to about 2k and the fuel trims still spikes up further more. What does this implies
Fuel supply issue (fuel pressure or injector clog).
By "Up further" I'm thinking you're asking if it gets more negative or stays very negative. If not, let me know. If so, then It could be a fueling issue (fuel pressure low, partially restricted injectors) or it could be an intake air meter reading. That could be a Mass Air Flow Sensor problem. It is also possible that a temperature sensor is reading too hot but that would be rare and would probably set a code for temp sensor.
What if you have stft at minus 8 at idle and ltft at positive 18?
That would be a total fuel trim of 10%. Given enough time the LTFT will lower to 10 and the STFT will be around 0. 10% is still a bit too much.
@@theroyaltyautoservice thanks for the reply! What are some things that could cause this? Vacuum leak or leaky fuel injector? Or maybe small boost leak?
👍
SHARP Royal Auto Service
From Nick Ayivor from London England UK 🇬🇧 ⏰️ 22:39pm
Hey Shorewood I have a automotive question can I contact you some way I'm having an issue with a toyota corolla 2001
Great video..