Aftermarket catalytic converter

[makymak]

Well, the funny stories with my Octy continue... 

 

Yesterday, after a cool festival, I went to ride my Octy back home and... Grooommmm, vroom vroom.... 

Taking a look underneath and the cat was missing... 

 

"OK, Maky. Take a deep breath, you're covered by your insurance" but with a damn restriction: the insurance will cover either a new aftermarket or a used original part. This is my contract due to age of the car. 

 

Spoke to my mechanic and said the market of used catalytic converters is very problematic in our area due to the rising stealings. So, he gave me the solution to buy an aftermarket. He told me that an aftermarket hasn't the quality of an oem but it would be ok if a quality brand. 

 

Should I go with the aftermarket? Or should I pay the difference and go for a genuine (considering the price, I doubt it). I don't know even if VW has any availability for such an old product... 

[varooom]

4 minutes ago, makymak said:

Grooommmm, vroom vroom.... 

Sorry, did you want me?

 

 

 

 

Yes clearly I am joking 😄

Ok, on a serious note, if they get stolen often, and also you have to take into account the age of your car, perhaps aftermarket will suffice.. but if you are thinking to keep the car long term, then maybe it's worth getting the genuine and hope the thieves don't strike.

Edited 25 February, 2023 by varooom

[makymak]

1 minute ago, varooom said:

Sorry, did you want me?

 

Yes, of course. If you bring your catalytic conv with you... 

[bigjohn]

On my old 2001 Octavia the original cat rotted through so I replaced with an aftermarket one that was easier to fit as it came with an additional flange between pipes. Lasted many years - still ok at the end of life of the car.

 

 

Edited 25 February, 2023 by bigjohn

[stratosg]

If it was me, I would go for a new  aftermarket one. Unfortunately used catalytic converters comes in an unknown state and with no warranty if it is dead. 

[sirlancelotksa]

Same thing happened to me, back in December 2021; the garage opted for an aftermarket catalytic converter.
On the following MOT it almost failed due to emissions, although I suspect that it was because of an aftermarket MAF that had also been replaced between MOTs, as they can be tricky.
Already bought an Hitachi MAF, that will be replaced before the next MOT, due in June.
Will leave feedback.

[makymak]

Unfortunately, it didn't went well. After the catalytic replacement I went for a long trip (350 km). I then connected the vcds and it gave me the

 

16804/P0420/001056 - Catalyst System; Bank 1: Efficiency Below Threshold

I went to the local garage (of my trust) and they measured the exhaust system. The CO was into the limits but quite high. The NOx same. But the HC were as triple as high than the limit, at idling. Above 300 ppm (while the upper limit is 100). This exactly garage had MOT'ed the Octy a year ago and the HC were 81 ppm at idling. I've done this year's MOT at another garage, after a major service (where some intake leaks were fixed) and the HC were dropped at 27 ppm (at idling), quite low for the age and mileage but still on the original catalytic converter. This test was made at 4th of January.

 

Nothing was done on the engine during the last months. The only change was the catalytic converter and the emissions went to the roof... 

 

Tomorrow, I will book the car back to my mechanic.

 

Any clues than the obvious (cat is not a quality part)? 

 

[makymak]

Quick question: how much should the λ (lamda) be at idling? AVU engine. 

[J.R.]

What are you measuring it with?

 

If you mean the Lambda read out on the MOT testers machine or printed on the certificate then it should be Lambda 1.0.

 

If you mean the voltage from the Lambda sensor then I think it is 1 volt although I have a feeling that wide band sensors have a different voltage, in any case the important thing is to see the voltage constantly swing from high to low as the fuelling alters example 07 volts to 1.3 volts, for this you need an analogue moving scale display multi-meter.

[makymak]

58 minutes ago, J.R. said:

What are you measuring it with?

I mean the actual afr. I'd like to know if at idling this engine operates near stoichiometric or leaner. 

You see, today at my mechanic's we took some exhaust measurements and the λ was 1.2 at idling; very lean. If the engine is supposed to idling near λ=1, then this indicates the problem lies rather with the O2 sensor than with the actual catalytic converter. The one-million-dollar question is how much can the after catalyst O2 sensor affect the mixture (supposing idling is a closed-loop state). The pre-cat O2 sensor wasn't replaced and was working absolutely fine before the incident of the theft so I guess it still does. We have a suspicion that the after-cat O2 sensor the exhaust shop sold us with the cat is a universal one, modified to fit the harness. 

[Breezy_Pete]

All petrol engines with cats need to run at stoic for the cats to work optimally. MOT has very tight tolerance 0.97 - 1.03 from memory.

Air leak in exhaust can make for dodgy tailpipe lambda reading, any chance there's such a leak?

 

[makymak]

Don't know for the moment if there is a leak. But can a leak raise the emissions, especially the hydrocarbons? 

[Breezy_Pete]

Doubt it, I was only thinking of the way-lean tailpipe lambda reading.

 

[makymak]

Thanks, Pete 

 

And thanks J. R.

 

If there are no leaks, can the after-cat O2 sensor be responsible for the engine idling lean?

Edited 17 March, 2023 by makymak

[J.R.]

Check it with a moving coil scale voltmeter, if it switching from high to low then it is doing its job but giving the wrong reading, I reckon it will be signalling a constant high rich reading (cant recall if that is the high or lwo voltage) and the ECU is going to its maximum default lean setting.

 

I think in the absence of a signal it goes to the safer maximum default rich setting, I had that on a 95 petrol Gaalaxy when the main dealer replacing the clutch under a recall left the O2 sensor cable dangling and the cooling fan blades cut it through, no EML light in those days, the car just used a lot more fuel and eventually blocked the catastrophic convertor.

[makymak]

Today, I visited the exhaust shop and they admitted they used a generic O2 sensor and they have to replace it with a suitable part. They did it (in front of me, so to have proof they did put the correct part) and after that, they done an emissions test. Unfortunately, the result was the same: at idling, CO=0.2% and HC=300ppm and lambda=1.2. Then they informed me they had to replace the converter as they don't see any other solution. I was expecting them to blame the car for the high lambda (lean mixture) but they said since the car doesn't throw a CEL and the only error is the above (16804), they had to replace the whole catalyst. They welded a different type (still a ceramic one) and they said this specific catalyst is for Euro 5 emissions control while the previous was for Euro 4 (what my car is). They did again an emissions test and everything went back to normal. At idling CO=0.05%, HC fluctuating between 20 and 80 with a tendency to stay close to 50ppm (well bellow the upper limit) and lambda=1.06 which is still lean but I guess well acceptable. 

 

I still will do an emissions test at a MOT garage I trust, just to be sure. 

Edited 18 March, 2023 by makymak

[makymak]

Good news! It passed the emissions test! I took a measure at my trusted MOT garage and it was well bellow the limits. 

 

Now, I have to see how long the catalyst will last. But that's a whole different story... 

 

Thanks for the advices!!!