P0420 + Petrol smell from exhaust

[samanaslt]

From last weekend's small trip of 300 miles engine light showed, upon checking code found out that it is P0420 - Catalytic converter system, bank 1 - efficiency below threshold. 
On different noncontinuous monitor screen it shows that "Catalyst Monitor Bank 1 - MID$21, Value 0.03294 - Minimum is 0.038735, Result - Failed 

Once error removed, light will come back after around 15 miles. 

Also there is Petrol smell outside the car, smell strongest next to exhaust tips. Currently there are no other symptoms and car runs smoothly. 

Could anyone advise, if this is indeed upstream oxygen sensor failed which needs replacing? Car currently just under 150k miles. 

Thank you. 

[scudney]

You might have a small exhaust leak close to the oxygen/lambda sensor 

[ColinBarber]

Exhaust leak then upstream sensor then injectors should be inspected first in that order before considering the cat itself is at fault. 
 

Unlikely to be something common such as the MAF sensor if only one bank affected. 

[samanaslt]

41 minutes ago, ColinBarber said:

Exhaust leak then upstream sensor then injectors should be inspected first in that order before considering the cat itself is at fault. 
 

Unlikely to be something common such as the MAF sensor if only one bank affected. 

I had some holes fixed back in October, as I had this warning coming after driving hundreds or thousands of miles. Never had petrol smell though.

After fixing havent had this warning till now.

I had to overpass cars on higher revs, so perhaps pressure did made a hole somewhere again.

How could a pinhole on exhaust cause petrol smell?

 

Thanks

[Spock66]

The petrol smell will be because the car is running too rich.

[Linas.P]

10 hours ago, samanaslt said:

How could a pinhole on exhaust cause petrol smell?

It is quite simple really, the sole purpose of oxygen sensor is to check if there is oxygen in exhaust gas. Hole lets in oxygen from outside and therefore makes oxygen sensor to incorrectly read like there is unburn oxygen in the exhaust, so the ECU thinks that it needs to inject more fuel to match the excess oxygen, as such too much fuel gets injected, whereas there are actually no excess oxygen and you end-up with unburnt fuel and thus petrol smell.

This most of the time results to incorrect error code P0420/P0430 displayed, because ECU then assumes it is Catalytic Converter fault for not burning excess oxygen and fuel, system simply does not account for the possibility that there could be hole in the exhaust providing this extra oxygen. As suggested, the most common reason for this code is exhaust leak near oxygen sensor.

Cats rarely (if ever) fails on these cars and when they do fail that happens at 200k+, but usually the entire exhaust rusts and crumbles arounds the cats before the cats themselves fail. So the common reason for cat replacement is usually rust, not that cat is no longer works. 

[samanaslt]

On 4/28/2024 at 6:00 PM, Linas.P said:

It is quite simple really, the sole purpose of oxygen sensor is to check if there is oxygen in exhaust gas. Hole lets in oxygen from outside and therefore makes oxygen sensor to incorrectly read like there is unburn oxygen in the exhaust, so the ECU thinks that it needs to inject more fuel to match the excess oxygen, as such too much fuel gets injected, whereas there are actually no excess oxygen and you end-up with unburnt fuel and thus petrol smell.

This most of the time results to incorrect error code P0420/P0430 displayed, because ECU then assumes it is Catalytic Converter fault for not burning excess oxygen and fuel, system simply does not account for the possibility that there could be hole in the exhaust providing this extra oxygen. As suggested, the most common reason for this code is exhaust leak near oxygen sensor.

Cats rarely (if ever) fails on these cars and when they do fail that happens at 200k+, but usually the entire exhaust rusts and crumbles arounds the cats before the cats themselves fail. So the common reason for cat replacement is usually rust, not that cat is no longer works. 

Went to couple of different places and indeed there is multiple holes in exhaust system, but the main culprit is driver's side midpipe to cat flange. Huge hole developing there. 
I was told in 2 different places that they are not doing flanges and they would need to change midpipe with cat 'pipe' which by the look on internet is quite expensive. 

Is it worth to try custom exhaust places to see if I can get new midpipe and weld new flange to cat pipe? 

Also, petrol smell is not coming from exhaust system after all, found a small leak on driver's side just before rear wheel, kinda underneath rear passenger driver seat. 
Not sure if it worth to make another topic, but mechanic said that they cannot really see where exactly it comes from and it would need several hours work to find out. 
From observation could be seen that it coming somewhere from top of tanks. 

As now I got less than half tank of petrol left, I noticed that petrol smell disappearing and its not as strong. 
I suspect this to be a hole in the tank at higher place as when  i had full tank, it was quite intense smell. With one small drop of petrol developing on road after keeping car overnight.  


Could somebody please tell me if it is actually worth to try to fix these issues, as I believe exhaust + plus petrol tank change would be very expensive? 

Thank you. 

[Linas.P]

4 minutes ago, samanaslt said:

Went to couple of different places and indeed there is multiple holes in exhaust system, but the main culprit is driver's side midpipe to cat flange. Huge hole developing there. 
I was told in 2 different places that they are not doing flanges and they would need to change midpipe with cat 'pipe' which by the look on internet is quite expensive. 

Is it worth to try custom exhaust places to see if I can get new midpipe and weld new flange to cat pipe? 

Also, petrol smell is not coming from exhaust system after all, found a small leak on driver's side just before rear wheel, kinda underneath rear passenger driver seat. 
Not sure if it worth to make another topic, but mechanic said that they cannot really see where exactly it comes from and it would need several hours work to find out. 
From observation could be seen that it coming somewhere from top of tanks. 

As now I got less than half tank of petrol left, I noticed that petrol smell disappearing and its not as strong. 
I suspect this to be a hole in the tank at higher place as when  i had full tank, it was quite intense smell. With one small drop of petrol developing on road after keeping car overnight.  


Could somebody please tell me if it is actually worth to try to fix these issues, as I believe exhaust + plus petrol tank change would be very expensive? 

Thank you. 

The first issue - honestly nobody is surprised about it, this is the case 99% of the time.

Strangely, I also run into the problem of exhaust places refusing to make "these flanges"... I really don't understand why, because those flanges are just standard flanges. So I suspect just need to ask around and somebody must be able to do it properly. I suspect they don't want to put the effort, because they make more by selling whole section, but that is just not good excuse. 

Last summer I was a bit in a rush and my flange was completely gone, so that is how "the fix" looked like. At that point I reckon it was not much of the loss, because there was no flange to speak of:

As for fuel leak - IT NEED IMMEDIATE ATTENTION!!!! unless you don't mind your car turning into fireball.

First of all this would be classed as "dangerous" fault in MOT, and for once I would agree with them. Secondly, it is genuinely dangerous to drive around like this, because top of the fuel tank is literally under your passenger seat and there is no metal between it and the interior so petrol is basically in your interior.

This is potentially not difficult to check, just pull lower part of passenger seat-up (there are 2 hooks) and you can check the top of the fuel tank. My guess it could be two main places, maybe 3 - the fuel pump ring is cross-treaded, the houses are damaged or leaking (or some idiot forgot to connect return line), or maybe some issue related with fuel pipe/breather hose. Any history of recent fuel pump work? Worst case scenario it could be physical damage 

like cracked fuel pump housing or hole in the tank, but that is less likely. But first step would be to check what is going on under the seat.