MAIN CATS REMOVAL advice re sensors

ray d

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Hi all I am sure this has been talked about before but I cant find anything but I am thinking of removing the main cats on slk 55 R172 but am not sure what will the sensors pick up and are they going to show up faults. Has anyone done this and had they any problems. Thanks
Ray
 

Cozy

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Hi Ray,

I'm not a 55 owner but on my C63, I added long tube headers. Granted, these are catted but the cats are located where the OE secondary Cats were and there's nothing where the primary Cats used to be. Both pre-cat and post-cat sensors are plugged in but there's no Cat in between them. I ran a while like this without a tune and I never received any codes or rough running. Hopefully the 55 ECU works the same.
 

brucemillar

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I think (I may be wrong here) that the ECU will just adapt to the new readings and not throw a code. But you may have to keep all sensors in situ (plugged into your empty pipes) or the ECU my complain that it can't find the sensors.
 

PobodY

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I take it these are not lambda sensors then?

No closed loop operation or fuelling adjustment without lambda sensors, but temperature probes the ECU generally couldn't care less about.
 

PobodY

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So if you disconnect the front lambda sensors doesn't it throw a code, or does it just stop trying to run in closed loop?

Obviously you don't need to have a catalytic convertor (legally you're supposed to have them for emission purposes, but the engine doesn't care either way because it's an exhaust thing), so the sensible suggestion would be to have a boss welded in to the new exhaust and screw them back in.
 
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ray d

ray d

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So far that all sounds good. I bought a second hand set of down pipes to take the secondary cats out (which I have done) but against the wife's wishes there is still more "V8 sound" in there and I WANT IT. I will be able to put the original down pipes back and rear section in when car is in for service / warantee work and then for MOT (I had a custom made Power Flow system with Res out X pipe in and sports silencers at rear). Hopefully someone here has actually done the main cat removal which will confirm all the replies.The worst thing I done is took the Jag V 8 F type out on a test drive with the active exhaust system on it and I SO want the same noise as it just sounded soooooo good. Deep down I think the wife is hoping I get the sound I want and she can relax a bit more and bring the cheque back out of hiding :bannana:
 
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ray d

ray d

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Checked the links and I am afraid it all went over my head :dk: It would be great if someone who has done it could come in and say if it either worked or not. I will wait in hope
 

daveenty

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If you remove both primary and secondary cats, the chances are that the car will throw P0420/P0430 codes, which are "Catalytic Converter Out of Threshold banks 1 & 2". This basically means that the downstream sensor cannot differentiate between the upstream one as the reading is too similar, i.e. the cat's not doing anything.

There are a couple of ways round this. You can buy a spacer which theoretically removes the downstream sensor away from the flow, though I don't personally know anyone who has done this, or you can have the sensors mapped out via the ECU, which is how I got rid of my annoying CEL light. Any competent tuner should be able to sort this out for you.
 

Alps

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as Dave says, you will need to map them out, not sure if they can be turned off in star also.
 
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ray d

ray d

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That is great I understand now, perhaps I would be best leaving it alone as it is still under warantee and I am pretty sure when it is in for service they put any updates in to the ecu so it might overwrite any mod. I was hoping that maybe the car might show up a fault but drive ok then I would put the cat pipe back in for service / warantee work
 

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