Suggestions on down pipe without cat and tune

[daughtersA4]

Hey guys,

I didn't dig for this info here so apologies if this has been discussed extensively. The cat on my 2012 A4 is toast and want to replace it with a downpipe without cat. What do I need to know here about dealing with the check engine light, I assume I need a tune after install? What if I don't do a tune? What down pipe should I be looking at? I have a Quattro, is the removal/install more difficult? Thought I read that somewhere and haven't cruised Youtube yet. I will be doing this install myself.

Thanks!

[A4x]

You do not need a tune, but you will get a check engine light when running the stock tune with a test pipe or high flow catted downpipe. This check engine light will NOT affect driveability or anything like that. Your car will continue to drive normally, except with the CEL illuminated. You will not pass California smog.

Install is not that difficult but totally dependent on your experience. Removing the stock bolts can be tough if they are old/rusted/etc. Make sure to use a lot of penetrating oil leading up to the removal. Check Youtube for DIYs and tips. Good luck.

Quattro vs FWD shouldn't make much difference.

[Chillaxin]

Hey guys,

I didn't dig for this info here so apologies if this has been discussed extensively. The cat on my 2012 A4 is toast and want to replace it with a downpipe without cat. What do I need to know here about dealing with the check engine light, I assume I need a tune after install? What if I don't do a tune? What down pipe should I be looking at? I have a Quattro, is the removal/install more difficult? Thought I read that somewhere and haven't cruised Youtube yet. I will be doing this install myself.

Thanks!

You can use a "defouler" that puts the O2 sensor far out of the exhaust flow. This may or may not prevent you from having a CEL on the dash. Stage 2 tunes can code out the signal from the post cat O2 sensor so you dont get a CEL.

[19birel]

Integrate Engineering Stage 2 paired with a test pipe from ebay (deletes the cat, but keep stock down pipe with resonator so it stay tame sound wise).

You'll pass emissions and the car will have a lot more pep!

EDIT: I just noticed you're in California, you'll fail smog without a cat both visual and the "sniffer" test. I heard Cali is also checking ECUs for remaps that aren't CARB approved (IE is not). I think you're only choice is to get another CAT.

[daughtersA4]

You do not need a tune, but you will get a check engine light when running the stock tune with a test pipe or high flow catted downpipe. This check engine light will NOT affect driveability or anything like that. Your car will continue to drive normally, except with the CEL illuminated. You will not pass California smog.

Install is not that difficult but totally dependent on your experience. Removing the stock bolts can be tough if they are old/rusted/etc. Make sure to use a lot of penetrating oil leading up to the removal. Check Youtube for DIYs and tips. Good luck.

Quattro vs FWD shouldn't make much difference.

Cool thanks for the info!

- - - Updated - - -

You can use a "defouler" that puts the O2 sensor far out of the exhaust flow. This may or may not prevent you from having a CEL on the dash. Stage 2 tunes can code out the signal from the post cat O2 sensor so you dont get a CEL.

I'm running defoulers now and they work to keep the CEL off. Thanks!

- - - Updated - - -

You can use a "defouler" that puts the O2 sensor far out of the exhaust flow. This may or may not prevent you from having a CEL on the dash. Stage 2 tunes can code out the signal from the post cat O2 sensor so you dont get a CEL.

I'm running defoulers now and they work to keep the CEL off. Thanks!

[daughtersA4]

Integrate Engineering Stage 2 paired with a test pipe from ebay (deletes the cat, but keep stock down pipe with resonator so it stay tame sound wise).

You'll pass emissions and the car will have a lot more pep!

EDIT: I just noticed you're in California, you'll fail smog without a cat both visual and the "sniffer" test. I heard Cali is also checking ECUs for remaps that aren't CARB approved (IE is not). I think you're only choice is to get another CAT.

I will have to deal with the smog check (thats what its called in Ca), there are some ways around this. Thanks.

[A4x]

EDIT: I just noticed you're in California, you'll fail smog without a cat both visual and the "sniffer" test. I heard Cali is also checking ECUs for remaps that aren't CARB approved (IE is not). I think you're only choice is to get another CAT.

There is no sniffer test. Smog is a plug in OBD check and visual inspection. If you can get past the OBD check (you can with a spacer for a few miles only) then there are other ways to pass the "visual" part.

[daughtersA4]

Do you guys know if these high flow cats pass California smog? Maybe this is the way to go if this is the case. Thanks.

[A4x]

Do you guys know if these high flow cats pass California smog? Maybe this is the way to go if this is the case. Thanks.

No they do not. They need a special EO number stamped on the cat to pass the visual inspection (I believe only Magnaflow offers this, and it is not really a "high flow" option).

[Matt Devo]

The cat on my 2012 A4 is toast and want to replace it with a downpipe without cat.

Just to make sure you or anyone else is looking at the correct parts -- the downpipe and cat are two distinct and separate components in the exhaust system: Turbo --> Cat --> downpipe --> rest of exhaust. A replacement for the cat without any catalyst is referred to as a test pipe.

[daughtersA4]

Just to make sure you or anyone else is looking at the correct parts -- the downpipe and cat are two distinct and separate components in the exhaust system: Turbo --> Cat --> downpipe --> rest of exhaust. A replacement for the cat without any catalyst is referred to as a test pipe.

Yes thanks. I realized this yesterday after researching parts and realized there was a difference between the two or maybe I should say three parts that makeup the exhaust.

[daughtersA4]

I did find a guy online that knocked all the catalyst material out of the stock cat and bolted it back up. This is appealing to me since it would retain the stock pipe with the CARB compliant codes for visual inspection and I could probably get by with the anti foulers for the smog check. I passed a smog check last year with the anti foulers installed. Guess the didn't look too closely.

I would even go as so far as to weld in a pipe on the inside to straiten out the flow.

Anyone on here do this? Looks like a pretty easy job using a spade bit, hole saw, hammer and chisel. Im looking for an inexpensive way to resolve the bad cat, not looking so much for the added performance. Any gains would be nice though of course.

[marcomarco]

Make sure you want to do this because your car when running will stink like a 1970's Challenger when parked...when in the drive thru... when at stop lights.

[daughtersA4]

Make sure you want to do this because your car when running will stink like a 1970's Challenger when parked...when in the drive thru... when at stop lights.

So the bad smell would also happen with a test pipe right? I have heard of there being a bad smell with a cat that is going bad but this is the first i'm hearing of a bad smell when a cat is removed.

[marcomarco]

Cat cleans up a crap ton of noxious fumes.

I haven't done this on an A4 but my titan had headers which deleted the two primary cats while leaving two secondary high flow cats in place.

It smelled so bad it was embarrassing. Your case probably won't be as bad... just letting you know.

[daughtersA4]

Yep yep understand. Thanks.

[RallyeBourne]

A few things from a fellow enthusiast behind enemy lines (California).

1). You were lucky to get by the visual inspection with the anti foulers. The rule of thumb is you cannot modify anything between and including the MAF housing to the rearmost O2 sensor. You found a lenient guy, stick with him.
2). The foul smell mentioned is just a gas smell. But it does get bad. And isn’t the healthiest to be breathing. It is present with bad cats because they are underperforming and not burning off the gasses. It is present with a test pipe because there’s no cat to burn off the gasses.
3). As far as passing smog with a tune, that is vehicle dependent, and I don’t know how the B8 reacts. I was able to pass my Subaru XV Crosstrek with a custom tune. But I know of other Subarus that have been caught. Kind of a crap shoot until the community can figure it out.
4). My suggestion would be to get a high flow cat for $350 or whatever, and when smog time comes around, reach out to the local euro community and find someone that will loan you their stock car for the duration of the test. It’s pretty common around here in SoCal. But a new cat is probably at least $1200. And you cannot legally buy a used cat from any shop in CA.


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