Any of you 2.7 owners remove the mid cats?

[TheAvgBear]

Like the title says have any of you with a 2.7 removed the mid cats? For some reason my allroad doesnt have flanges or flex pipe north of the mid cats. I plan on doing some work to the tranny to solve my leak probelms, but i can only remove the last half of the exhaust (there are flanges after the cats, under the driveshaft. So the cats and exhaust are under the tranny in the way, unless I remove the downpipes from the turbos, which looks next to impossible!

So my plan to get access to the transmission was, to go to a nearby shop and have buddy add flanges farther up on the front side of the cats so that i can come home and take the exhaust off.

I live in Canada and don't have emission tests to meet. The ar has 185,000km (115,000mi), so the cats are prob near the end of their lives anyway. I was thinking of maybe just removing the cats completely, adding new pipe and freeing up some back pressure. I've been looking into the issues with the O2 sensor all afternoon, and i've only really came accross write ups about the o2sensor on the pre or upper cats directly after the turbos. So i'm just wondering if anyone of you have removed the mid cats, and if so what did you do to the O2 sensor to avoid a CEL? Just remove it from the cat, add a bung for it in the pipe and use spacers or non-foulers? Does this work for the 2.7? Anything else a junior like me should be aware?

[ENDEE666]

Many of us run no cats, myself included. Neither of my 2.7 cars have them. Removing them is good for quite an increase in power as well. They are very restrictive. Removing the pre-cats at the turbos is also a big help. Look up "Piggie Pipes" or gutting pre cats, or you can also get SSAC or similar downpipes for very cheap, and then have flanges welded to them.

I don't know how Canadian inspections work. Here in NY, they no longer put anything in the exhaust to measure gasses. But removing the main cats will immediately cause a CEL for the rear O2's and that will make you fail. So you will need to have your ECU flashed to code them out. Then your ECU will think the cats & O2's are there and properly functioning. The spacers will not likely be enough to compensate for no cat at all. Those typically only work for a high flow cat.

[TheAvgBear]

Many of us run no cats, myself included. Neither of my 2.7 cars have them. Removing them is good for quite an increase in power as well. They are very restrictive. Removing the pre-cats at the turbos is also a big help. Look up "Piggie Pipes" or gutting pre cats, or you can also get SSAC or similar downpipes for very cheap, and then have flanges welded to them.

I don't know how Canadian inspections work. Here in NY, they no longer put anything in the exhaust to measure gasses. But removing the main cats will immediately cause a CEL for the rear O2's and that will make you fail. So you will need to have your ECU flashed to code them out. Then your ECU will think the cats & O2's are there and properly functioning. The spacers will not likely be enough to compensate for no cat at all. Those typically only work for a high flow cat.

Oh well that is very good to know! Thanks. Aside from the CEL would there be anything else that comes with removing it? I may just remove the cats since im going there, and then hopefully get the ECU flashed before I get my tranny leak taken care of. If not I can live with just a CEL until the code can get flashed.

And I have looked into doing the piggie pipe mod quite a bit! It really interests me, but the the turbos and the bolts downpipes look pretty tight and hard to get at without removing the engine. I was just in there replacing the axles and figured I have more stuff to worry about before I should get into that.

What is the best way to get the ECU flashed to code the cats out? Is it possible with VAGCOM? Or where is the best place to go to get that done? I dont know much about it. I really appreciate the insight! Thanks!

[TheAvgBear]

http://www.audiworld.com/tech/eng53.shtml

I came across this write-up just now, that talks about adding a diode to trick the ecu into reading the correct O2 voltage. Buddy seems pretty confident about the technique. But it is directed at getting a correct reading because the precats have been gutted. Anyone try this? Or know if the same technique would work for my scenario? With having the precats left alone, but removing the midcats and just having the o2 sensor directly in the pipe

[TheAvgBear]

I hate to be annoying but I just wanted to bump this thread. I have an appointment booked for this friday to do something with the exhaust. I dont want to remove the midcats and then be cursed with a CEL. I called around my city and the nearest place that will flash an Audi ecu is ~10hrs drive away. If the diode or non-fouler/spacer technique wont work for the secondary O2 sensors I may just leave the cats in for now. But if anyone has had success with this before I'd really appreciate the insight. Thanks.

[estomax]

the mid cats wont give you a CEL. the rear o2 sensors are ahead of them so you can safely cut them out if you want to.

i left my mid cats in and removed my main cats when i got a tune (and got the CEL coded out). how smelly is the exhaust with the mid cats removed also for those who have done it?

[suth31]

the avgbear, can you please clarify which area of the exhaust you want to modify? any pictures?

[TheAvgBear]

the avgbear, can you please clarify which area of the exhaust you want to modify? any pictures?

I dont have pics available at the moment. I will try to get some tomorrow.

But basically, there is 4 cats in total. The primary or precats with their O2 sensors, right after the turbos on the down pipes. Then there is the secondary or midcats with their O2 sensors in the middle of the car, basically right under the rear output shaft/beginning of the driveshaft. I have no flex pipe or flanges between the midcats and downpipes like lots of people seem to. The first and only exhaust flange I have is after (rear end) of the midcats. So i can only remove the last-rear half of the exhaust system (from basically mid driveshaft to the mufflers), without removing the downpipes at the turbos. My transmission is leaking pretty bad and I want to remove more of the exhaust to be able to get better access to the transmission/transfer case/ front diff, and hopefully find my leak(s). So my plan was to take it to a shop, and have them add flanges at the bottom of the down pipes in front of the midcats so i can take it home and remove more of the exhaust.

Then I was wondering if, instead of just adding flanges infront of the midcats and going home. Maybe I should just still get them to add flanges at the bottom of the downpipes, but then remove the midcats entirely, get them to add flanges at the bottom of the downpipes, then just add straight pipe with an added bung for the O2 sensor.

So ultimately the exhaust would be untouched precats with their untouched O2 sensors, then straight pipe with the secondary O2 sensor installed in straight pipe, then finally the mufflers. But I was unsure about doing this bc of the CEL issue, and how easy it would be to get around it. Most of the write ups on the issue I found have been on the precat O2 sensor bc of everybody doing piggies.

I apologize for the earlier confusion, and I dont mean to sound short at all. I'm just trying to explain it the best I can. Thanks so much for any input that anyone is willing to supply

[TheAvgBear]

the mid cats wont give you a CEL. the rear o2 sensors are ahead of them so you can safely cut them out if you want to.

i left my mid cats in and removed my main cats when i got a tune (and got the CEL coded out). how smelly is the exhaust with the mid cats removed also for those who have done it?

By removing the main cats do you mean the piggie pipe mod? With removed precats?... Also my rear O2 sensor is installed directly into the mid cats, not ahead of them. They are more so on the front end of the cat, but still directly in the cat. So I'd think that they would read a different O2 speed if I removed the midcats and just put the sensor in straight pipe? Thanks for the input.

[estomax]

yeah i did the piggie pipe mod on my car but left the downstream cats in. the o2 sensor is not doing anything with the downstream cats i am confident you can remove those and not get a CEL. either way if you do it is time for a tune anyway :)

Marko