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Putting CATs back in; sensor?

Discussion in 'A3/S3 Forum (8L Chassis)' started by Squirrelofdoom, Oct 3, 2012.

  1. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 3, 2012]
    Hi guys,

    My previous owner chopped the CATs out of the exhaust and welded in straight pipe. The flanges are still there, and my MOT is coming up, so I'm looking to buy a standard CAT section to pass the MOT (got a few sources lined up). Question is, how do I fit the sensor back? When my CATs were removed, the sensor went with it....and if I buy a new sensor, where do I need to wire it to?

    Cheers guys,
    Aran
    #1
  2. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Oct 3, 2012]
    Sod cats, find a friendly moter haha.
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  3. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 3, 2012]
    lol, trust you to say that Dani!! Mr. I've got a 3" custom :p
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  4. vrbob
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    vrbob Thats no Moon, Thats a space station!

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    [Oct 3, 2012]
    the post cat lambda screws into the cat and then has a connection under a little plastic cover where the 2 wires join up so i would suggest you check if the other part of the wire is still there or not.

    Does your EML light come on on the dash? cos if not it can be coded out so you could effectively fit a cat without the sensor and just put a bung in the hole
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  5. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 3, 2012]
    err, call me stupid, but where is this "little plastic cover" mounted so that I can get underneath my car and check it's still there?

    Also, without a post-CAT lamda, will my cars fuel trim not be all over the place?
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  6. vrbob
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    vrbob Thats no Moon, Thats a space station!

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    [Oct 3, 2012]
    Not sure if affects fuel or not much it just measures the effeciency of the cat as such. As soon as i put my 200 cell cat on the EML light came on which is what happens if the lambda is working and it detects a cat issue. So if you dont have a sensor currently and you have no EML light its either been coded out. Or maybe they have just hidden the lambda sensor somewhere under the car but still connected electrically.

    The little box that cover the connector is on the drivers side about 10inches in and about 2ft back from the front wheel. It kinda looks like a tupperware box held on with 2 plastic nuts
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  7. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 3, 2012]
    Cool, i'll have a look tomorrow. I currently run a stock map with no EML light, so maybe they have hidden it somewhere...
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  8. vrbob
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    vrbob Thats no Moon, Thats a space station!

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    [Oct 3, 2012]
    My guess is it hidden somewhere then and just reading lots of clean fresh air coming out of your decat lol hence the no EML light. Yeah if you find said box then it should lead you to your lambda sensor or whatever is connected to your car to make it think it has a working one.
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  9. beachbuggy
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    beachbuggy Well-Known Member

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    [Oct 3, 2012]
    Just map the rear O2 sensor out. It'll stil get through mot, it's not really needed.
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  10. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 3, 2012]
    well, if the sensor is there I will plug it in. If not then Dan, are you able to map it out? At some point I need to discuss with you Stage 1 mapping anyway
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  11. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Oct 3, 2012]
    What can i say, the ladys love the 3" girth ;) haha. On a side not, my mates amk s3 got decatted at the same time and his eml lights always on and always logs a vcds code.

    what engine codes your car mate?
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  12. Squirrelofdoom
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    Squirrelofdoom Member

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    sigh...i was waiting for someone to make a 3" joke!! Mine's an APY
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  13. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 4, 2012]
    also, Rob, clear some of your PMs so I can send you one! :p
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  14. vrbob
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    vrbob Thats no Moon, Thats a space station!

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    [Oct 4, 2012]
    Done now mate ;)
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  15. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Oct 4, 2012]
    Lmao, you set me up for it.

    dude if its a apy it ony has a pre cat lambda haha, bless. So you dont have to worry about the second lambda as you dont have one, same as me :).
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  16. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 4, 2012]
    say what?! boomtown!! lol Ahhh Dani, what would I do without you?
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  17. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Oct 4, 2012]
    I honestly dont mate, i really dont haha.

    So what you sorted out cat wise then?
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  18. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 4, 2012]
    hahaha, that enough ego boosting for you now? :p

    Probably gonna take Robs old ones. Car is going down to JKM in a couple weeks anyway and he's based nearby, seems like a good shout. I'll use them for MOTs and then whip them back off and put the straight through back on afterwards
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  19. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Oct 4, 2012]
    Ok lol.

    Sounds like a plan mate, should be easy enough todo.
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  20. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 4, 2012]
    yerp, quick question while i'm at it. If i'm swapping that section of piping in and out, does that section have those wire mesh crush pieces between them? Or is it just the metal flange up against each other which seals?
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  21. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Oct 4, 2012]
    No i beliee they have some kind of flange mate, you could just use some cheap exhaust putty, not like the cats will be in long enough and just sae the seals for the decat!
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  22. Squirrelofdoom
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    Squirrelofdoom Member

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    [Oct 4, 2012]
    fair point, your wisdom is useful once more :p
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  23. vrbob
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    vrbob Thats no Moon, Thats a space station!

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    [Oct 4, 2012]
    The downpipe end has a flange gasket put if its just for mot purposes a spot of putty will do for a short time. The other end that connects to the back box has a sleeve clamp and does not need any sort of gasket.

    As for the post cat sensor that's all good then as I have put a bung in the hole where that would go so that's sorted.
    #23

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