Help! Need a new cat for my 35i

[TonyE89]

Hi people. I need a new cat for my 2009 s35i and the only place I can seem to find one is from BMW. they want £580 inc VAT. I might need to change both of them so so anyone know of anywhere that would sell them for a cheaper price?
Thanks.
Tony.

 

[R.E92]

I think there are 4 in the 35i. Two primary cats right after the engine then another two further down the exhaust.

It's quite common for people to remove their primary cats and install downpipes without a cat so you may be able to find a user that will sell you their removed ones.

If you are out of warranty I would just get rid of the cats, save some money and get increased engine power and torque. You need a tune to remove the cat warning code but you can have that done using MHD for £100 total spends.

Out of interest how has your current cat failed?

 

[TonyE89]

It's the 2 further down the exhaust. There's a rattling sound coming from the exhaust on the over run and when I had a diagnostic run on the car it came up with 2 fault codes: 29F4 DME catalytic converter conversion and 29F5 DME catalytic converter conversion 2. I don't know what they mean. Any ideas?
I have emailed a company called longlife who specialise in making exhaust systems to see how much it would be to make one for my car and I'm just waiting on a reply.

 

[R.E92]

I don't think the rattling and codes are linked. Seems strange to have both of the lambda codes thrown at once.

I think you are probably either having issues with the O2 sensors or someone has previously installed catless downpipes on the car.

What's the history on the car? Was the previous owner a modder? Also has any work been done recently on the car?
You can get those codes thrown if the O2 sensors are installed in the wrong locations by an incompetent mechanic.

The rattling on overrun is almost certainly wastegate rattle. It's really common and manifests during overrun when the wastegates are seated.
Does it sound like this video?
[youtube]v5koIcGsPm4[/youtube]

You can visually check the downpipes on in the Z4 just by looking under the bonnet behind the engine from the drivers side. Take a photo if you aren't sure what you are looking at. Most catless downpipes will be nice shiny looking things, the stock ones are a metallic brown.