[kern417]

Originally Posted by Skyhigh

Your main problem is not that it detached. Your problem is it MELTED! It would have melted even if it was "stuck" in place. It detached because it melted, it did not melt, because it detached....

Converters falling apart is a common thing.... typically after 3-400 000 km. But they normally don't melt.



The quality of the cat converter makes all the difference! Remember that its primary role is to convert exhaust gases to a level satisfying specific environmental standards. One cat converter achieves Euro 6 with a 500 cell design, another with a 200. How do you think that works? It works by using different (more expensive) materials in order to boost the efficiency whilst reducing the cell count. So no - cat converters are not all the same. Which is why you also don't have that many companies to manufecture them I reckon. It is not really a backyard task I suspect.

Another question - are you losing coolant? I just remembered that a freind of mine destroyed both his DPF and the cat converter (melted) because his engine was burning coolant (cracked cylinder head).

melting and coming apart are two different failure modes. I've seen melted/blocked cats that stay in place. This one looks like it came detached and then began melting and collapsing since he was still driving with it clogging the pipe.

Also passing emissions specifications isn't that difficult, but it is very expensive and takes time. So having the certification doesn't mean it's higher quality, just that the manufacturer went through the legwork to get it. Generally most won't go for the cert because it has a marginal increase in sales and profits. It also doesn't cover everything. Like in the US, meeting national EPA standards doesn't mean that you meet all emissions laws, especially in states like California. So it all depends on the manufacturer, what they think is worth it and their marketing strategy.

It also goes to note that most OEM catalytic converters aren't immediately after the cylinder head/turbo like on BMWs. The more I think about it, the more I'm settling on the fact that it's a design flaw in the exhaust. You don't hear about this on VW, Honda, etc. even with cheaper systems. I know many people with 400+hp Big turbo kits that have aftermarket catalytic converters in place.

[jackstrath]

Theres a reason rally cars have there cats basically as tail pipes..... anti lag would basically blow it to bits in seconds...

[Skyhigh]

Originally Posted by kern417

melting and coming apart are two different failure modes. I've seen melted/blocked cats that stay in place. This one looks like it came detached and then began melting and collapsing since he was still driving with it clogging the pipe.

A detached CC would start making noticeable rattling noise and be pushed back by the gases whilst maintaining its shape and orientation (it cannot rotate and clog, whilst still sound and shaped as a pie, even if detached). Seen that on old vehicles many times. This one quite certainly detached because it compressed due to the melting. This is pretty obvious.

Also passing emissions specifications isn't that difficult, but it is very expensive and takes time. So having the certification doesn't mean it's higher quality, just that the manufacturer went through the legwork to get it. Generally most won't go for the cert because it has a marginal increase in sales and profits. It also doesn't cover everything. Like in the US, meeting national EPA standards doesn't mean that you meet all emissions laws, especially in states like California. So it all depends on the manufacturer, what they think is worth it and their marketing strategy.

Talking about different things here. You are talking about EPA certification (which has little to do with emissions), I am talking about meeting emission standards which are controlled in every European country on every vehicle tech test (done annually or every 2 years, depending on the country)! Europe cares about what people breath.

The high quality catted DPs from respected manufacturers maintain the emission standard of the vehicle (e.g. EU6), which is the whole point. Hence each CC is subjected to regular emission tests by authorised facilities. The compliance is achieved and maintained by using higher quality / higher purity materials (i.e. precious metals). This is what drives the cost up, not the simple metal pipe and not the one-time certification.

It also goes to note that most OEM catalytic converters aren't immediately after the cylinder head/turbo like on BMWs. The more I think about it, the more I'm settling on the fact that it's a design flaw in the exhaust. You don't hear about this on VW, Honda, etc. even with cheaper systems. I know many people with 400+hp Big turbo kits that have aftermarket catalytic converters in place.

And how often do you hear about this on BMWs in general, especially with stock converters (the majority)?

[Wires]

This only happens when you get "clever" and crank the burbles to max.

For those that do not understand what cat's actually do, they get hot and start glowing orange. Their purpose so ignite any unburnt hyro-carbons (aka fuel) so that the exhaust leaving the car is has no unburnt fuel.

When you ask for the "burbles" to you sending larger quantities of raw fuel into the cat, it ignites, and you get a pop. If that cat starts to melt (it was never designed for actual combustion), then it you gets this perpetual "hammering" effect from the burbles which would result in what the OP has seen.

If it's popping in the cat, pressure will go backwards and hits the turbo, which would technically want to drive it backwards. No different than what happens during pre-ignition inside the cylinder.

[Skyhigh]

What you are saying is partially true, but are you saying "no cat, no pops" (since you are saying you need a cat to ignite the unburned fuel)?
Because that is not the case, as we all read around here

And what you describe is not exactly how a cat works it is the chemical reaction that improves the exhaust gases, not any combustion that happens in it but yes - it only works efficiently when up to temperature (which is why we have cat pre-heating phase when we start the engine).

[kern417]

Another one bites the dust.

[Oktom2]

I know this is an old thread but I just encountered a very similar cat failure on my N55 M2.
https://f87.bimmerpost.com/forums/sh...0#post27017700
A bit less advanced but very similar looking shape of shrinking.