The Trainer #65: Fuel Trim Explained - What It Is , How It Works, And What It Can Tell You

Is great video I just subscribed

Sooo....rich is lean and lean is rich. Unlike a carburerated engine where rich is rich and lean is lean.

I need a guy like this for my car, mpg has dropped by 30% after am oil and air service. 3 garages have put the car on the diagnostics and said there's no codes so nothing is wrong.

Wow! Thank you for this very basic but informative video.

Very helpful video 👨‍🔧 thank you,

Engineers have made this work very tricky!!! Too many parts and sensors. Ugh

If a maf sensor is reading bad it will make both banks run rich or lean not just a single bank? Correct?

Thanks for sharing your knowledge. Going park it on the chip watch all your videos 🫶🏻

👍👍

I hope you are still with us. Keep sharing your wisdom.

Does this apply to P2177 and P2188? I’m getting both codes and I’m so confused. My STFT at idle… -25%. Cruising 0-10%, under high load +25%. LTFT +20%

Thanks.

Solid video. Im getting a pending B2 lean code occasionally but the B2S1 voltage is fine and active. The LTFT is around 11. I doing see any other redflags....... curious what the ECU is seeing/understanding. Thoughts? Thanks!

FLAT RATE TEST DRIVE - an excellent idea!

Excellent video. THANKS

Thank you so much.

My long term fuel trim is at 0.00 no movement .
My maf sensors is .001-.002
What could be the issue here ?

What causes my LTFT to be at +10.8, I drive for half hour, shut engine off, 30 minutes later I start the engine and the LTFT is now +14.1 and stays there while driving half an hour? STFT varies +/-4%. According to my scan tool, the MAF (4.5 g/s) and O2 sensor appears to be working properly. I haven't been able to find a vacuum leak. Fuel pressure is at 40 PSI. Stock 2002 Mustang GT. Injectors never have been changed. No codes. Car drives fine otherwise. Someone mentioned that it could be intake manifold gaskets.

Wish I had found this site a long time ago. THANK YOU.

Thank you so much sir🙏🙏🙏

Very nice presentation from the ground up— helps so much in understanding how it all fits together!

2011 Buick LaCrosse 2.4 ecotec.... My short term fuel trim #2 (O2 Sensor band 1 sensor 2) is always 92% no matter what.

I just had those codes show up on my 2002 Toyota. Ran the MAF procedure from their Service Bulletin and saw that it was out of spec. Replaced and fixed. Apparently it was under reporting the air weight.

Just found your channel. You are a gifted instructor!

If your not sure how rich (or lean) the ratio is, would unplugging the MAF sensor be a way to reduce harm to the cat? Would it bring it back to default mix?

I've just had a new cat fitted today, yet now see a prior 'too rich' code and a Maf voltage too low code. So am now concerned that the new cat will burn out fast, which would be far from ideal, given the expense of the replacement.

Always the very best love you videos all of them period.

Long Term is the window of time the adaptive memory dictates the fuel trim, Short Term is live data calculating to learn the parameters for the adaptive memory to update the Long Term. The O2 sensor signals lean below .45 volts & rich above .45. The Engine Controller only cares about that threshold & uses that to determine fuel trim. .. in other words the computer calculates the % of time that the O2 sensor is past the threshold of .45 volts & does that each time the threshold is crossed.

Look old man, I’ve been a senior master ASE tech/mechanic for over 25 years, after listening to you going on and on about your diagnostic theory I feel the need to say…… thanks. I’m still learning. Just subscribed and I’ll be going through all your previous videos and checking in for new ones as well.

I know Sir that you could clear up this problem why is it these AES techs don't know about this code help.

Please tell me how to what to do about code p06de AES techs don't know how to check and clear this code techs turned off engine light but it came back on.

Great video. I learned it slightly different but, basically the same in that the computers response could be compared to an old style tv. The short term is like a fine tuning and the long term is like changing the channel when the fine tuning reaches its limit.

Hello what about if my long and short term stay at 0%

Thanks so much Pete

Been studying your videos past few days thank you for your wisdom and knowledge I appreciate it

He made it look complicated. It's so simple

Shrtbank1 17%

So basically modern fuel injection is a PID

Wow awsome tutorial " Sir " 👍👍

Great vid.👍👍👍👍

I have suburban 2007 flex with p0171/p0174. It came after p0175 and the injectors changed. The alcohol was 50% and the fuel trim was reset, and it dropped to 3-4% but now it missfire, cant drive, barely idle .Then the other two code came. The new maf, fuel pump, throttle, new ignition cables. Smoke test for leak showed nothing. What can it be?? Evap? Map? Fuel pressure?

Does anyone on here know why an 06 nissan pathfinder 4.0l would run rich on 1 bank and lean on the other bank accompanied by a p0300 (random multicylinder mis fire) and a p0333 (knock sensor high voltage)

Obviously great info and well presented. Just read the comments. I’ll subscribe and join all the other binge watchers.

Super. Thank you. VERY well explained to this DIY.

Every code is a top-10 DTC

THANK YOU FOR TEACHING US VERY VERY CLEAR

Great method in your delivery approach to understanding fuel trims . Well done sir ✅👍

I guess a V6 could be a front and back sensor right but actually usually the code or the computer say bank one and Bank two and you have to figure out if it's on one on the left the one on the right the one in the front or one in the back bank one or Bank two

rear fuel trim, that's a new worm hole for me.