I have a 99' A4 1.8T with 100K miles on it and I have gotten the CEL P0422 for catalyst below threshold bank 1 several times and now when I rev the engine and let of the pedal I can hear a rattling noise coming from the cat area but it only happens above 2000rpm. The cat is probably shot so im gonna replace with a high flow. How much do cats run for an audi?

 

get a cat delete pipe about $175 @ Renn-Art.com

 

Dont bother with a new cat. Get a test pipe -"a high flow". You should get new 02 sensors too at that mileage.

 

Alright I found this https://www.renn-art.com/Main.asp?make=1, now i just plan on getting some new o2 sensors as well. Do you need anything else in order for the test pipe to work, oh and that completely gets rid of the cat right?

 

also do I have no worry about any CEL with the testpioe ?

 

Which o2 sensors shoul di get from ecs tuning there are a bunch of diferent kind how do I know which one I need?

 

actually i was wondering since we are on the subject, does anyone have a test pipe? i just got one and havent installed yet and want to know how much difference it makes.
I think that on ECS tuning by the way, it says year for the O2 sensors and also which one it is. There should be two on the cat, one before and one after. it should say on the description.

 

I have my test pipe, bought from renn-art (it's atp test pipe accually), I have stock 0² sensors and no cel.

 

Thats the same one i got! How is it working for ya? notice a difference?

 

Really depends on the rest of your mods... if you're big turbo'd, you need a HFC or a test pipe. If you're stock, don't count on much of a difference. I just installed a full exhaust with a HFC and didn't notice a whole lot... I did notice some, but nothing crazy. I'm still k03'd.