P0420 code with a side of gas smell

Hello everyone .... again

On my drive home I got a repeat of the P0420 code the truck had when I first bought it, cleared it per previous posts advice in this forum and it shows up as pending with 1 min on my new fancy code reader.

Read some more and checked for exhaust leaks, I checked by holding my hand close to every joint or gasketed area in the exhaust system (from my brand new OEM mini header all the way back through the 222k old piping, cat, and muffler) with no leaks detected.

Did further research and found an awesome video post detailing the science of what trips a 0420 or 0430 code so I did some live stream monitoring on my code reader and I'm not sure what I'm looking at... hopefully someone can help decode the numbers?

I also noticed I have a HEAVY smell of gas at an idle, I mean makes you wanna go to sleep kinda heavy. That smell has been persistent since I dropped the rebuilt motor back in about 300miles ago. Checking the fuel system I have no leaks what so ever but I wanted to mention it in case it helps

The following pictures are of all the data points at idle, 1500rpm, 3000rpm and 5000rpm (all done in first gear in a wide open parking lot)

Idle



1500 (on the gauge)


3000 (on the dash)


5 x1000(those numbers behind the wheel)


I would consider those numbers the avg of what was shown...I expected the O2S11 (V) number to oscillate because it's supposed to correct? At at idle the value never dropped below .75 wouldn't that cause the brainbox to think there's an efficiency problem (because the rear sensor is mimicking the front sensor) and throw the P0420 code?

 

I believe you are understanding that part about the rear O2 sensor not oscillating and causing the ECU to trigger the P0420.
Isn't P0420 catalytic convertor not reach threshold or something? And you smell gas, which could be uncombusted air/fuel mix.
Maybe the sensor is functioning correctly and your cat convertor isn't converting properly?

Oh and you noticed the MIL line I'm sure, you're gonna see it all over now and be like wtf? How did I not notice it before?

 

The exact words for the code per my reader said "Catalyst System Efficiency Below Threshold (Bank 1)" what you say makes sense in that if the cat isn't catalysting my sensors are actually functioning properly and the ultra rich is entirely out of the exhaust.. I like that answer


In my defense this is the first time I've used these fancy features and AS SOON AS I read that MIL line I sayz to myself "oh that @cruiserguy!"

 

And the way you describe the smell is the most common way I hear that particular condition, the cat not doing its thing, that's how it's usually described. It's a particular smell, not raw fuel, but not regular exhaust by far. Certainly noticeable. Now how do we verify that is what's actually going on???

 

Does any one have a drug sniffer dog trained to smell exhaust fumes?! I'll pay him in scooby snax

But in more seriousness the smell is definitely not raw fuel, I've spilled enough of that on me in my life to know it's more.... exhausty. We used to have emissions in this state, what a weird time to wish they hadn't gotten rid of them!

 

Yeah that's a dead catalytic convertor, amigo mío.
They say the best aftermarket one for us is magnaflow. OEM is supposed to be big coin

 

Also we want to make sure whatever caused that one to die is addressed so the new one doesn't fail prematurely. Wait didn't you fix some condition of something you had going on, I forget now. Was the other thread with MIL lol

 

Oh buddy we've got issues ALL over the place

The other thread was talking about another member having fuel pump issues.. but you have chimed in on a couple of my threads. Transmission stuff being the most recent but we talked before that when I dropped in the rebuilt motor. When I first bought the trucks so many moons ago the MIL was on for P0420, misfire in cyl 1 and something else. Compression test showed cyl 1 was dead at about 80 lbs lol. Previous drove it like like for 2 or 3 months until the clutch burnt up on him.. that's when I swooped in and inherited this beautiful headache..... I still don't know why the steering rips to the right when I hit the brakes hard but one problem at a time, I didn't learn that was an issue until I could finally drive on the hwy


But back to the task at hand. Thank you for the input, I'll start pricing a complete exhaust system from the manifold back.... manifold is brand new might as well make everything else new as well

 

@cruiserguy is ot possible that one failed just due to age? It has 222k mileage on it so I'm kinda thinking it's just as tired as the rest of the truck


Are there other things I should check to make sure I dont have a legit fuel problem?

 

First thing, worn cat's don't convert the unburnt HC to H20 and C02, so you smell raw fuel, this is normal.

Secondly, a leaking injector will wreck a cat and lead to the same smell.

But.

Your long term fuel trim is good. +10 -10% is considered ok.

It's just a worn cat.

 

Oh I see bishop84 is here, he's a real good tech and will understand the data from the scanner much better than I. But seeing the STFT and LTFT will be the key to knowing your running right in that stuff

 

@Bishop84 cool, thank you so much for your input! Just so I'm clear and I remember correctly in the future; the acceptable range for the long term fuel trim is +or- 10%? Is there a special sweet spot I can strive for to make optimum performance? Or am I looking to much into it... I planned on putting bigger injectors in and i just want to know what to look for

 

your catalytic convertor is no longer functioning within specs. This is determined by comparing the reading from the rear 02 sensor to the front 02 sensor. To make it easier to understand, the front 02 sensor is continually monitoring the 02 (oxygen) level in the exhaust and if there is too much, a lean condition, more fuel is injected into the motor. Taking this signal and converting it to a human understandable form it looks like the teeth of a saw... peaks and valleys of differernt heights. If the catalytic convertor is doing ist job the rear 02 sensor will have an almost flat line reading. If the PCM "sees" that the rear 02 sensors pattern matches the front 02 sensor it knows that the catalytic convertor isnt doing its job.

leave the stock injectors in it if they are working... larger ones will only cause problems.

 

@Glamisman that all makes sense to me, but just to clarify the values you got that info from are the O2S11 and O2S12 numbers, correct? With 11 being the front and 12 being the rear?

So the higher value indicates a rich condition? And a lower value is more oxygen, making it a lean condition?


Thank you, you're input is also so helpful

 

yes... 02S11 = 02 sensor, bank 1 sensor 1 where bank 1 is the cylinder bank with cylinder #1 on it. 02S12 = bank 1 sensor 2 and in this situation it is the 02 after the catlytic convertor. Depending on the vehicle, usually high end cars with V12 motors there can be as many as 6 to 8 02 sensors.

 

https://www.yourmechanic.com/estimates/toyota/tacoma/exhaust-fume-odor-in-car-inspection

 

get a flashlight and on the drivers side peek into the gap between the rear cab and bed to see if if theres any wet gasoline leaking out from the cover that's bolted to the top of the fuel tank, this area gets corroded and the gasket under the fuel sending unit cover fails, sometimes you can replace and it holds up, it most often the corrosion in that area means a new tank is in order.

 

So the way I got those measurements and metrics to click in my head was like this:
That fuel trim number/value reported in the scanner is what the ECU is doing to account for the reading its getting from the O2 sensor. So it it's a positive value next to the stft or ltft that means the ECU is adding fuel to the air/fuel mixture.
Like bishop above said, anything within + or - 10 can be considered within spec.
Like you also alluded to, O2 sensors or A/F sensors definitely can lose their ability to work at peak efficiency with age. Even without any DTCs or obvious issues, it's not unheard of for folks to get a lil better performance, maybe mpg improves back closer to original, etc.
I definitely wouldn't replace those sensors with the expectations of improving how the engine is running, though that can happen

 

That's a good point. We have seen that here on the board a couple times too. Though I think he said he WASN'T smelling straight gasoline

 

mine threw that code and I first replaced both O2 sensors, code still on, smelled raw gas when exiting truck, peaked in that area found wet gas coming from the fuel sending unit cover. theres a couple DIYs on replacing the gasket/fuel pump/fuel tank on the search function around if that's your case