Fuel Trim Imbalance Case Study, presented by John Thornton

[@8power0]

I have been reading Mister Thornton articles in automotive magazines for years , if I am not mistaken i think he wrote an article on a Nissan maxima many years back with a misaligned crankshaft flywheel . That said after reading that article i was able to land a good job at an Asian automotive repair shop because at that time no one where i live could have figured it out . This Man is Legendary those who have the chance to learn from this man....... it will only be you that would be the bottle neck in your automotive future with his guidance .

[@josedejesusvelazquez6863]

I am lucky to be one of those, tanks John. 👍

[@scientist100]

Wow, the shop said they detached the cat and no change. I've seen way too many videos where technicians tend to believe a little bit of what other people have said they have done but somehow it comes back to that first suspected issue that ends up being the problem, never trust what other people say and do your tests. The IAT sensor tip is a great direction for checking backpressure, that is a new one for me, thank you for the tip.

[@ThunderbirdRocket]

Watching it again ! This is GOLD !!

[@bookoobeans]

For anyone still reading comments on this video: If the O2 sensors are easy to access, I wonder if it would have been more efficient shop practice just to screw in a pressure gauge and compare the banks this way?

[@AutoDiagnosticsPK]

Yeah, its done like that to diagnose exhaust restrictions

[@romanjaspe4172]

Interesting, thanks so much Mr thornton 👍

[@780brando]

Great explanation, you must reset the fuel trims & drop the exh simultaneously if your going to check for a restricted exh/cat that way, the learned fuel trim wasn't going to let that engine run very well. I do see lots of cam timing problems as well causing similar issues.

[@SomeoneSaid-nu6qd]

How do you reset the fuel trims?

[@CFlo93]

@@SomeoneSaid-nu6qd I would also like to know the same.

[@DJ-tn7vj]

Excellent training mr John

[@autodiagnerdzllc8966]

Great video John! Hope to return to your classes soon! Take care sir, hope your doing well.

[@jdtractorman7445]

Excellent video. Just curios as to why on 3.0L and smaller engines the grams per second compared to liter size of the engine does not apply?

[@chuemoua6834]

Good explanation! One of the best I’ve ever heard

[@johnmitchell8925]

The scan tool is the first thing that should have been hooked up

[@clintonadams5006]

Good for learning electronic controls being old school would been using mechanical gauges vaccum compression and exhaust pressure, oh never assume previous Diagnostic been their more often than needed.old dog learning new ways.

[@JoelAutomotiveInaction]

great teacher

[@rainbowdiamonds2865]

Very interessting Video, thanks and all good for you, John.

[@johnjauregui3528]

How does ethanol affect ECM/PCM fuel trim calculations? Does it require the same 14.7 ratio calculations or some other ratio? If so does the ECM/PCM sense whether the fuel is ethanol or gasoline and use a different ratio for ethanol? If the ECM/PCM assume gasoline is used and does not adjust for the use of ethanol what is the impact on air/fuel calculations and fuel trim outputs? How does this affect scanner outputs, rich, lean, etc.? Is there a YT video that addresses these questions? Bottomline: How does the ECM/PCM adjust for these two different fuel types with different optimum air/fuel ratios, or does it not, and what are the impacts on scanner readings and diagnosis? Again, is there a YT video that addresses these questions?

[@trxtech3010]

Good video. I have the issue with my 98 4.3 S-10 and everyone says what the las guys says is "Cloggged Cat, Bad Fue Pump, Bad Spider injectors, bad 02 Sensors etc" yet I have replaced allll oofff thoseee.

[@scientist100]

Same issue with fuel trims bank to bank? Be sure to reset trims after detaching the cat.

[@drjimjam1112]

Vacuum or exhaust leak?

[@d.d4184]

Brilliant. Thank you.

[@billsullivan8812]

2008 Ford ranger V6 vulcan engine . LTFT Bank 1 was running negative -.8 at idle , would not change. LTFT on Bank 2 at idle was 9 percent. Drive down the highway both long term fuel trims were within acceptable limits, but press more on gas pedal #1 LTFT got more negative and # 2 LTFT got more positive. Checking the number 1 catalytic converter oxygen sensor B1S2 with the truck fully warmed up , it was found the sensor was exactly duplicating the upstream sensor, switching from .2 to .8 volts. Number 1 catalytic converter was obviously no good and partially obstructed as well.

[@alexlongpre4527]

So, when the shop stated that they dropped the cat. and it didn't change anything about the condition, were they blowing smoke up yours, did they remove only one side, and happened to choose the wrong one?

[@scientist100]

What I think happened, they did not do a KAM reset when they detached the manifold/cat. Just a guess but that's what probably happened.

[@kyletuttle9064]

Great tip thank you for sharing.

[@IAMNOSLEEP]

Thanks for sharing... Cheers.

[@SomeoneSaid-nu6qd]

Fantastic educational video.

[@abelhwata-mufakose3237]

Great 👍

[@jibranbaloch7650]

Nice

[@mikechiodetti4482]

That makes sense especially if the entire bank has a problem.

[@rodvan-zeller6360]

At 10:00 would global mirror dedicated? or is the substitution not allowed in global?

[@simclardy1]

thank you. very helpful

[@nowayjose596]

What's the difference between the PCM operating in closed loop with a fault vs open loop? If it's no longer listening/responding to the O2's input and just using stored values, isn't that just open loop?

[@jenniferhammond9714]

Hey buddy, hope you are well.... Brian Hammond

[@tharakanuwan9986]

Kudos to U Sir

[@ThunderbirdRocket]

Fantastic tutorial ! Thanks !!!

[@gmtech2012]

Am I the only one that noticed the MAF breakdown was for a 6 cylinder engine when he said in the beginning that it was a 5.4 V8?

[@jorgetorres-bf1bk]

Great video !!! Thanks

[@abdouallahuniverse5689]

Fuel trims sometimes are not accurate, meaning not real, caused by defective or aftermarket or dirty or old OEM MAP or MAF sensors, like mine, the MAP sensor, which causes both fuel trims to be at 12 to 14 percent. I thought that I had a vacuum leak, but it was the aftermarket Delphi MAP sensor reporting wrong air flow or air pressure to the ECM, I just put back the OEM sensor and the fuel trim went down to 5 percent. I couldn't believe it, almost 10 percent extra, unnecessary fuel was injected into the cylinder, I don't know why oxygen sensors didn't report rich condition? And now I installed new OEM honda Denso bought from eBay, and the fuel trim went to zero percent now, sometimes 1 percent, sometime minus 1 percent sometimes 2 percent. I couldn't believe it. The initial issue was rough idle and sometimes engine misfire, and fibration, but it was the ignition electric connection wires that were loose at the aftermarket start button system. Basically, I created the problem over time by using a bad quick disconnect connector. I replaced the connector, and the problem partially solved: rough idle and misfire, but the fuel trim problem got fixed by installing the old OEM MAP sensor back.

[@tonyfremont]

It shouldn't reach 5psi of back pressure at full throttle.

[@ronaldmahoney1283]

Dropping the drivers side exhaust should have been all you had to do to determine the problem!

[@juanlazar8945]

Bloody interesant, 😮😮😮

[@hoosieronthefarm7677]

Why wouldn’t you first take out your temp gun shoot the manifold then the cat??? Just don’t understand why if you think you have a restriction in the exhaust why you wouldn’t check temperatures, IDN? Maybe to learn the newbie’s a long way to check exhaust restrictions Done…….. 30min of time waisted

[@williemoon7522]

i have watched dozens of these videos trying to figure out why my V6 is rich on bank 2 .. i thought i had found the answer here .. but my cat temps before and after are exactly the same on both banks .. i have high long term readings on bank 2 and soot builds up on the exhaust pipe ..

[@drjimjam1112]

Did you do a smoke test?

[@johnmitchell8925]

Sounds like you way over complicated this

[@clueless6559]

Another great USA repair shop fail ,

[@drjimjam1112]

The country you’re from doesn’t have car shop failures?

[@IamReadyToRock]

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