9N3 GTI Downpipe and Lambda Sensors

[Bflat]

I'm not sure of the logistics involved, but my APR downpipe with 200cell highflow cat and 42DD o2 spacer will be for sale soon and conveniently enough I'm heading to Auckland in mid March. We could work something out if you'd like?

[PoloGIT]

No I wouldn't get too excited there.
I may be wrong or I may have misunderstood the course of the thread so far but I'm pretty certain that if you are phase 1 and you run a de-cat you will get a cat code. You would definitely have to run a spacer to have a chance of avoiding it but still might be likely to get one even then. For example I was advised by Carformance that they sometimes even see 100 cell people get codes that are running a spacer so that suggests to me that you'd be running the gauntlet with a proper de-cat pipe. If you don't run a second o2 sensor spacer then you may be ok with a 200 cell cat (since they still represent some flow hindrance) but a 100 cell will most likely code. I was advised to go 200 cell with a spacer by Carformance to be sure.
Gav was talking about Phase 2 before which codes out the cat error so that it will be ignored by the ECU. If your on phase 2 you can have any cat you want or no cat at all and it won't matter. Phase 1 tune is expecting to see a Cat though.
My two cents.....If the ecu will throw a code when you have no cat versus when you do have a cat, then it stands to reason that there is still a significant flow difference that the prescence (or lack thereof) of a cat makes . Cats will dull dB's but they are not designed to do this so I wouldn't keep one in the system for that reason alone. If you don't have to have a cat by law, then save the dollars, run the de-cat pipe for best possible initial flow, keep the resonator in place to stop low rpm droning, and throw some money at a new high flow muffler. Yours is most likely flogged by now and a restrictive sponge compared to some really high flowing yet extremely quiet mufflers that are around now. Thats probably the cheapest way into some quiet free flowing-ness! Spend 30 bucks on the correct second 02 sensor spacer and you'll probably be lucky.

Thanks sambb, there's some interesting points in there that I'll take into account.

So is the gti supposed to have a resonator? I'm 99% sure mine hasn't got one, just cat and then straight to the stock muffler - will have to get under there and have a proper look. That (and the questionable state of the old muffler) would explain why it sounds a bit boy racer atm.

[sambb]

mmm some do some don't from memory. Mine is an 06' and has one. Its just a narrow one between the cat and the rear beam.
Another thing you could do is run with the de-cat pipe, but get it flanged when its installed at the point where a cat would normally go and a flanged slip joint put onto the rear section. That way you can always go to a cat later on if its too noisy without having to have the whole front pipe removed for welding.

[PoloGIT]

I've just received my new Lambda sensor from the UK and have ordered a Remus Exhaust system at a great price from Auckland All going well, I'll get those two fitted by the end of the week and will also have a chat to the exhaust man about downpipe and cat/decat etc, which will be next on the list. Hoping with the new lambda sensor I'll be seeing the back of the CEL...for the time being at least.

[PoloGIT]

Remus rear end and pre-cat lambda sensor installed. Cleared down error code with VAG-COM after I picked it up. Really happy with the sound - a bit loader than stock (assuming my old system that's seen 220k sounded stock) but not too loud. The engine light seems to be gone for good, so looks like we replaced the right sensor Car is certainly going a bit better, especially at the bottom end - it seems to spool up a lot quicker. How much of that can be attributed to the exhaust, as opposed to the sensor, I don't know.