Page 1 of 2 12 LastLast
Results 1 to 18 of 21

Thread: Gutting precats

  1. #1
    Registered User Beardown1's Avatar
    Join Date
    Sep 2013
    Location
    SW Michigan
    Posts
    146

    Gutting precats

    I'm planning on gutting the precats this weekend while I wait for my turbos to be returned from Midwest Turbo Connection. I have searched and found conflicting info on how to prevent a CEL. Can I just use spacers on the front O2s or do I have to relocate or have them coded out? I have an APR tune so coding them out would require me to send in my ECU. So spacers would be the best choice if that will work.

    As as always, thanks for the great advice fellas.
    '03 RS6: Full APR EMCS/TCU, Nurburgring Bronze 19x8.5, Freshly Rebuilt Turbos, Gutted Precats, Stern Racing Mounts, SAI Delete, Aux Radiator Delete, Venair Hoses, Koni Yellows.....

  2. #2
    Registered User MaxRS6's Avatar
    Join Date
    Mar 2009
    Location
    Here
    Posts
    2,673
    I would just send it in to APR and let them do their thing
    210K miles rolled

  3. #3
    Registered User Bigglezworth's Avatar
    Join Date
    Mar 2007
    Location
    Cowtown, AB
    Posts
    2,232
    The pre-cats are after the upper O2 sensors. Gutting the cats shouldn't affect these sensors. The reason for coding out the upper O2's usually has to do with the difficulty in accessing them once they fail or require mileage driven change-out.
    '02 S6 Avant Silver - Pokey | Carbon Black/Ebony RS6 w/ stuff - darn quick | '03 Daytona Grey/Ebony RS6 w/ more stuff - quicker yet | '91 NSX CDN issue with 6spd & BBSC - quicker yet and then some | '87 Buick GNX OEM clone w/ lots of stuff - quickest hands down

  4. #4
    Registered User Beardown1's Avatar
    Join Date
    Sep 2013
    Location
    SW Michigan
    Posts
    146
    Really? So just gut'em and go? Man I would hate to get everything buttoned back up only to have a fault or MIL.
    '03 RS6: Full APR EMCS/TCU, Nurburgring Bronze 19x8.5, Freshly Rebuilt Turbos, Gutted Precats, Stern Racing Mounts, SAI Delete, Aux Radiator Delete, Venair Hoses, Koni Yellows.....

  5. #5
    Registered User Bigglezworth's Avatar
    Join Date
    Mar 2007
    Location
    Cowtown, AB
    Posts
    2,232
    I do believe so yes. That said, I have not started my ride here up yet after the tranny swap so can't confirm one way or the other. A few other members who have gutted their pipes should be able to confirm shortly for you. I know I will have to address some CEL item(s) because I've removed the SAI system. I did leave the EGR's in after SteveKen suggested they were doing a bit more than just temperature management for the ECU effort. They weren't broken or coding, so what the hell. I also left the upper O2's in and haven't decided yet if I want to (or in fact need to now that precats are gonzo) code them out also.
    '02 S6 Avant Silver - Pokey | Carbon Black/Ebony RS6 w/ stuff - darn quick | '03 Daytona Grey/Ebony RS6 w/ more stuff - quicker yet | '91 NSX CDN issue with 6spd & BBSC - quicker yet and then some | '87 Buick GNX OEM clone w/ lots of stuff - quickest hands down

  6. #6
    Registered User
    Join Date
    Jul 2008
    Location
    Out there
    Posts
    7,780
    Its the secondary O2s that you put spacers in.

    Gut the primary cats.

    Put the engine back in.

    See if the MIL comes on.

    If it does then try the secondary 02 spacers.

    Last resort....code out the secondary 02 sensors. This can all be done with the engine back in the car.



    Quote Originally Posted by Beardown1 View Post
    Really? So just gut'em and go? Man I would hate to get everything buttoned back up only to have a fault or MIL.

  7. #7
    Registered User Zmey's Avatar
    Join Date
    Jan 2013
    Location
    Chicago
    Posts
    105
    Spacing secondary o2 didn't help in my case, car would get cel after 150miles. I had to code them out with Eurocharged tune.
    6spd complete

  8. #8
    Registered User ttboost's Avatar
    Join Date
    May 2009
    Location
    CT
    Posts
    2,457
    I'm sure it's an oversight, but you CANNOT code out front/upper O2 sensors. They do ALL the important work. Front O2's are also BEFORE the precats, so they don't really care what comes after. I'm sure everyone here meant coding out the rears, but it might be confusing to someone who doesn't know better. Unless I am mistaken, the fronts do ALL the fuel math, rears are just for emissions...
    2013 Audi S8

  9. #9
    Registered User Beardown1's Avatar
    Join Date
    Sep 2013
    Location
    SW Michigan
    Posts
    146
    Good info Ttboost. I finished the first one in less than an hour with a 2lb hammer and chisel. Wasn't so bad. A few pieces fell down towards the back of the exhaust and don't want to come out. Is that a big deal? How worried should I be about getting them out?
    '03 RS6: Full APR EMCS/TCU, Nurburgring Bronze 19x8.5, Freshly Rebuilt Turbos, Gutted Precats, Stern Racing Mounts, SAI Delete, Aux Radiator Delete, Venair Hoses, Koni Yellows.....

  10. #10
    Registered User RAUDI's Avatar
    Join Date
    Jul 2013
    Location
    Bremerton, WA
    Posts
    264
    Quote Originally Posted by Beardown1 View Post
    Good info Ttboost. I finished the first one in less than an hour with a 2lb hammer and chisel. Wasn't so bad. A few pieces fell down towards the back of the exhaust and don't want to come out. Is that a big deal? How worried should I be about getting them out?

    You should get them out. Just an idea here. You could connect a blower motor/shop vac on blow mode to the rear of the exhaust and try to get it back out of the front that way.... Or gut the back ones too. Plugged cats = failed cats.
    2004 S4 Avant - 2003 Avus Silver RS6 MT (sold)
    Public link to Onedrive.com 6MT Files
    https://1drv.ms/f/s!AjZTWt7Mgp7SiVfliUkt64Ao6iSE

  11. #11
    Registered User Beardown1's Avatar
    Join Date
    Sep 2013
    Location
    SW Michigan
    Posts
    146
    I guess I will buy a flexible magnetic pickup tomorrow and try that as we'll. mine are all non-flexible so it's yet another tool I get to add to the arsenal.
    '03 RS6: Full APR EMCS/TCU, Nurburgring Bronze 19x8.5, Freshly Rebuilt Turbos, Gutted Precats, Stern Racing Mounts, SAI Delete, Aux Radiator Delete, Venair Hoses, Koni Yellows.....

  12. #12
    Registered User 4everRS's Avatar
    Join Date
    Nov 2009
    Location
    MN
    Posts
    2,405
    Yes. Get that material out of there.

    Yes. Have APR code out the downstream O2's. Also have them add left foot braking. Search for German tuning shops near you that sell and service APR. You could bring the car to them and have them bench flash what you need.
    Avus Silver RS6 - Viper Stage 2 ECU/TCU - Water/Meth Injection - Frozen Rotors - Hbars - clear corners - Hella smoked tails - gutted precats

  13. #13
    Registered User Bigglezworth's Avatar
    Join Date
    Mar 2007
    Location
    Cowtown, AB
    Posts
    2,232
    Quote Originally Posted by ttboost View Post
    I'm sure it's an oversight, but you CANNOT code out front/upper O2 sensors. They do ALL the important work. Front O2's are also BEFORE the precats, so they don't really care what comes after. I'm sure everyone here meant coding out the rears, but it might be confusing to someone who doesn't know better. Unless I am mistaken, the fronts do ALL the fuel math, rears are just for emissions...
    Mike is correct here. I errored with what I typed and clarify as follows:

    The 'upstream' sensors directly behind the turbos are the actual O2 sensors. You CANNOT code these out. The downstream sensors are not O2 sensors, but rather 'catalyst sensors'. They monitor only and confirm from an emissions perspective the condition of your catalytic convertor(s). You require the O2 sensors to address fuel management. If you get rid of all catalysts in your exhaust system and replace with straight pipe, you can code out thte downstream sensors.

    Quote Originally Posted by Beardown1 View Post
    Good info Ttboost. I finished the first one in less than an hour with a 2lb hammer and chisel. Wasn't so bad. A few pieces fell down towards the back of the exhaust and don't want to come out. Is that a big deal? How worried should I be about getting them out?
    Turn the pipe upside down andn bang on the side walls with a hammer. It cannot plug up the catalyst inside since the catalyst material is so fine. The large and small pieces that I had fall down the pipe all came loose along with all the dust. If you have a piece that is binding on the side, that is a complication that I'm sorry I don't have a recommendation on how to correct aside from cutting the pipe open and rewelding.

    Quote Originally Posted by RAUDI View Post
    You should get them out. Just an idea here. You could connect a blower motor/shop vac on blow mode to the rear of the exhaust and try to get it back out of the front that way.... Or gut the back ones too. Plugged cats = failed cats.
    You wouldn't gut the rear cats. You would simply cut them out and replace with straight pipe. I contemplated doing that with the precats, but I didn't have quick access to the welder at the time and was optimistic I could get it done in an hour. Ended up taking almost three, but still done without cutting out and rewelding a piece in place.
    '02 S6 Avant Silver - Pokey | Carbon Black/Ebony RS6 w/ stuff - darn quick | '03 Daytona Grey/Ebony RS6 w/ more stuff - quicker yet | '91 NSX CDN issue with 6spd & BBSC - quicker yet and then some | '87 Buick GNX OEM clone w/ lots of stuff - quickest hands down

  14. #14
    Registered User RAUDI's Avatar
    Join Date
    Jul 2013
    Location
    Bremerton, WA
    Posts
    264
    Quote Originally Posted by Bigglezworth View Post
    You wouldn't gut the rear cats. You would simply cut them out and replace with straight pipe. I contemplated doing that with the precats, but I didn't have quick access to the welder at the time and was optimistic I could get it done in an hour. Ended up taking almost three, but still done without cutting out and rewelding a piece in place.
    I was mostly kidding as I know he doesn't want to do that, but gutting can be an option for someone that wants to keep the appearance of stock. If I were to remove them I would do it by gutting. That way the state inspectors would have something the shape of a cat to look at under there.
    2004 S4 Avant - 2003 Avus Silver RS6 MT (sold)
    Public link to Onedrive.com 6MT Files
    https://1drv.ms/f/s!AjZTWt7Mgp7SiVfliUkt64Ao6iSE

  15. #15
    Registered User ttboost's Avatar
    Join Date
    May 2009
    Location
    CT
    Posts
    2,457
    Stock downpipes are expensive and hard to find. I didn't want to bastardize mine. I made my own ones from scratch, so as to maintain my stockers (we have emissions here too). Not worth the aggravation to gut the cats...unless you cut them right at the cat, gut them and weld them back up. You can find KO4 flanges if you look around. I was lucky and found a set of mangled downpipes, so I started at the gutted precats and fabricated from there. Complete catless is the way to go, if you can. If you can't weld, bring your stock downpipes, flanges and new pipe material to a welder and tell him to call you when they're done.
    2013 Audi S8

  16. #16
    Registered User TozoM8's Avatar
    Join Date
    Nov 2009
    Location
    Chicago
    Posts
    448
    The pre-cats are not ceramic so banging on the side will not brake them loose. You heed to chisel /drill it out. Get a pair of O2 sensor bungs/plugs. Remove the secondary O2 sensors from front of the main cat and plug the holes with the plug. Drill new holes after the main cat and weld the new bungs there. Install the secondary O2 sensors there and you will have no codes. This is the proper way to do it and this is how they have it on cars without pre-cats.
    05 Cayenne turbo

  17. #17
    Registered User Bigglezworth's Avatar
    Join Date
    Mar 2007
    Location
    Cowtown, AB
    Posts
    2,232
    Quote Originally Posted by TozoM8 View Post
    The pre-cats are not ceramic so banging on the side will not brake them loose. You heed to chisel /drill it out.
    To clarify, my comment about banging was to remove residual pieces that fall down the pipe adter chiseling out the cat and can hang up on the side wall of the pipe or become wedged.
    '02 S6 Avant Silver - Pokey | Carbon Black/Ebony RS6 w/ stuff - darn quick | '03 Daytona Grey/Ebony RS6 w/ more stuff - quicker yet | '91 NSX CDN issue with 6spd & BBSC - quicker yet and then some | '87 Buick GNX OEM clone w/ lots of stuff - quickest hands down

  18. #18
    Registered User Beardown1's Avatar
    Join Date
    Sep 2013
    Location
    SW Michigan
    Posts
    146
    Whew.........finally got it all out! There was more left in there than I thought.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	image.jpg 
Views:	149 
Size:	74.0 KB 
ID:	14780  
    '03 RS6: Full APR EMCS/TCU, Nurburgring Bronze 19x8.5, Freshly Rebuilt Turbos, Gutted Precats, Stern Racing Mounts, SAI Delete, Aux Radiator Delete, Venair Hoses, Koni Yellows.....

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •