My 2009 535i has bad front and back cats. We straightpiped the back ones and now the exhaust is cloudy sometimes, and it still starts up pretty rough. The exhaust guy told me to either get new front cats ($700 each) or flash the ecu and get rid of the front cats too. I'm
not worried about emissions because we don't test in our state.

I was wondering how can an ecu tune get rid of cloudy exhaust?
And how much does it typically cost to tune an engine to run without cats?

Thanks for the help. It's greatly appreciated.

 

I have a couple of ways for you to to fix your problem, if it's really the cats that are your problems.

First of all, a lot of people with 535is get catless downpipes (i am one of them), so they can sell you their cats

Or you can use this VRSF Catless Downpipe Fix E82/E90/E92 07-10 BMW 335i & 08-10 BMW 135i so their wont be a check engine light, I also have that because i am running catless

 

Awesome. So if I get the catless downpipes, and the O2 sensor downpipe fix, that will be all I need? Or do I still need to get an ecu flash?