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.

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 .

5 STAR VIDEO , EXCELLENT DIAGNOSIS .

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?

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.

Watching it again ! This is GOLD !!

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

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.

Interesting, thanks so much Mr thornton 👍

Excellent training mr John

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

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

Brilliant. Thank you.

Thanks for sharing... Cheers.

great teacher

Great tip thank you for sharing.

Great video !!! Thanks

Fantastic tutorial ! Thanks !!!

thank you. very helpful

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?

Kudos to U Sir

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.

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

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.

Great 👍

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?

Nice

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

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?

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?

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

Bloody interesant, 😮😮😮

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

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

Sounds like you way over complicated this

Another great USA repair shop fail ,

increíble