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  1. #1
    VXRed blooded
    Join Date
    11th July 2017
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    Question O2 sensor and decat

    just wondering who has done what when removing the CAT at the turbo.?
    Also what effect has it had on MOT tests?
    looking to ideally remove both Cats but i suspect I'll need to put a sports CAT in somewhere.

  2. #2
    VXRed blooded
    Join Date
    3rd September 2015
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    403

    Default

    Did not remove the main cat myself.

    But here is what to expect:

    OEM Downpipe hold the main cat, and 2 O2 sensors one on each side of the cat.
    The first one is for adjusting the air/fuel ratio and injection.
    The second one is to ensure the cat is working well.

    If you remove the first cat only (and go with bigger DP for performance), the 1st sensor is unchanged, but the second one will light MIL and you may not pass MOT pollution test anymore.

    If you remove the second cat only, there is no sensor on it, so you simply remove the secondary cat, get more pop and sound and still pass MOT.

    If you want to remove both there are 2 possibilities:
    1 - remove main cat and set a sport cat on second one. You still need to relocate the second O2 sensor after the sport cat.
    2 - go full decat (or double decat) - No more pollution tests as there is no cat anymore, need to touch the MAP to avoid MIL lighted up.

  3. #3
    VXRed blooded
    Join Date
    9th June 2015
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    386

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    When you remove both CAT's it will fail the MOT, so you would need to refit one for the MOT then remove again. When you remove the primary you will get the EML on, this can be turned off when you have the car remapped after removing the CAT's.
    The sports CAT will also need to have the car remapped and the EML turned off, but will pass an MOT.

  4. #4
    VXRed
    Join Date
    10th August 2017
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    You can also use a "spacer" or "defouler" for the secondary o2:
    https://www.ebay.co.uk/itm/UNIVERSAL...sAAOSwc2FaPbGT
    ^^Australian^^
    Car 1: 2016 Insignia VXR (Mods: none installed)
    Car 2: 2003 Mk7 Accord 2.4 (Mods: plenty)

  5. #5
    VXRed blooded
    Join Date
    11th July 2017
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    328

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    Quote Originally Posted by fredoops View Post
    You can also use a "spacer" or "defouler" for the secondary o2:
    https://www.ebay.co.uk/itm/UNIVERSAL...sAAOSwc2FaPbGT
    do they work on these cars... ive heard mixed reports on other cars

  6. #6
    VXRed
    Join Date
    10th August 2017
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    Quote Originally Posted by genman View Post
    do they work on these cars... ive heard mixed reports on other cars
    worked on the Saab 9-3 Aero 2.8T in the US, dont see why it wont work here, besides, one i posted have 3 different inserts
    ^^Australian^^
    Car 1: 2016 Insignia VXR (Mods: none installed)
    Car 2: 2003 Mk7 Accord 2.4 (Mods: plenty)

  7. #7
    VXRed blooded
    Join Date
    11th July 2017
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    328

    Default

    yeah thats a fair point... should have remembered that from my own Saab Turbo X days though i kept it stock

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