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Folks,

Car is due its MOT very soon and after that i was looking at getting bypass pipes fitted to the car to get rid of the cats, i know its probably illegal but will it damage the car in any way, will the car suffer from any lack of smoothness and will my current APR chip require remapping?
Would i require a performance cat back exhaust to take advantage of the bypass pipes?

Current exhaust is a stock one.

So many questions

Thanks in advance.

Steve.

Not suggested on the S4.

It has pre and post cat sensors that will bring up an engine check light and / or put the car into a performance limiting limp mode if it detects that the catalysts are working below efficiency.

Some of the early 100cell race cats did this too, and I have just had to swap from 100cell cats to 200cell on my s3 because of the same problem.

I know a lot of the guys in the states are running with the cats removed, may be worth a PM to Verruckt.

I would also be very interested in this for the RS4... Not that I am a cheap stake. I just cannpot afford the cats...

HI, i've just fitted milltec d/pipes & cats as part of my ko4 / engine re - build , i've only got pre cat o/2 sensors fitted (as standard). I'ts a y2k s4 , ,if your does not have any post cat sensors you can run it with no cat's .
From what i could see the standard s4 d/pipes have 2 cats per side , the first is in the collector after the turbo @the top of the d/pipe, the 2nd is the one under the car that you can see !!!.
The first looks like it's a 100 or 200 cell unit , the second 400 cell.
If you want a 100 cell cat you can buy them for £250-275 ea( ifyou want more details send a pm)then get a now d/pipe made .

grizz

Yes, some guys in the US run without cats. Many remove the pre-cats and relocate the secondary O2 sensors to behind the main cats.

To my knowlege, the CEL will NOT put the car into limp mode...just annoy you with the CEL light if you don't run cats.

Otherwise, talk to APR as they do have special codes for test pipes which ignore the cat efficiency codes.

Verrückt wrote:To my knowlege, the CEL will NOT put the car into limp mode...just annoy you with the CEL light if you don't run cats.

I'm not sure about the CEL, but the CAT temp sensor can put the ECU into limp. I know because it happened to me once. I've no idea why, and nor did AmD, but now I just get intermittent DTCs.

I remember when the car was in limp it was very rainy. So my theory is that the cats were colder than normal and I was accelerating hard. So my ECU decided that I should not be allowed to pollute the atmosphere any more.

I don't think the CEL came on. All I remember was pushing the go pedal and only getting about 0.4 bar on the gauge.

Hmmm think i'll leave that one then, thanks folks.

The cats can be removed and the chip can be reprogrammed to accomodate this. It is a matter of changing 1 bit in the chip, but of course, the most difficult is knowing which bit

Mihnea