[Denny1232]

Hi guys, I have been a long time reader of these forums and they have been great in helping me out with fixing problems with my car. But lately I been having a problem I can't seem to find anywhere on this forum, which is why I am posting for the first time.

To start off, I have a 2008 BMW 335xi that I bought maybe a year ago. No major problems to date except this one. For the past week I have noticed my ambient temperature getting hot really fast, like 110degree Celsius with 20-30 minutes of casual driving. when it gets to about 115degees Celsius and I accelerate, certain times my car will misfire, shake and eventually go into limp mode. For example, I was driving on the highway going about 120km/hr, and when I tried to accelerate my rpm at 2000 spiked to 4000, down to 100 and just kept on fluctuating until I went into limp mode.

I eventually brought it to a mechanic and he found chunks of charcoal in my exhaust system. See attached photos. I'm not sure what is the cause of all this. Maybe the chunks in my exhaust is causing it to overheat and go into limp mode??? Any advice will be kindly appreciated.

[Buug959]

I'm not sure what's causing your problem but that is not charcoal. It is the guts of your catalytic converter. And it looks as though it has gotten hot enough to start to melt which is pretty friggin' hot.

[oVeRdOsE.]

Originally Posted by LemansE90335xi

I'm not sure what's causing your problem but that is not charcoal. It is the guts of your catalytic converter. And it looks as though it has gotten hot enough to start to melt which is pretty friggin' hot.

Ive already got this issue, and it was the inverse, engine temp raised because the catalytic converter broke.

why it broke ? i don't know. Probably a mix of age, more power than OEM, and those crazy outside temperature variation. Like -26°C and +2°C in the same day. And a crazy fluctuating %RH. welcome to nordic countries.

OP will need new catalytic converter to avoid code and awful exhaust smell

[Denny1232]

Thanks guys. i have a vrsf catless downpipe so I never thought i would have any problems with my cats. I totally forgot about the secondary cats.

I ended up just chopping off the secondary cats, now my car runs smooth, no misfires.

[JonOhh]

Sounds like it wanted its secondary cats gone anyway... That's actually quite impressive. Those things have to get HOT (or knocked really hard, which can dislodge the honeycomb structure, cause a restriction, and cause things to heat up from there) to look like that.