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  1. #1
    VXRed
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    29th September 2014
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    Default Astra J VXR - How To Remove/Install Primary Catalyst

    Guys, my MoT failed on emissions - CO2 only. The Primary has been removed but still had the Secondary fitted, the plan was to leave this for emissions pass only. Yes it will fail regardless if any CAT is missing but just depends upon your MoT inspector at that time....

    This guide will tell you how to remove/replace your Primary catalyst, it is purely descriptive and no photos as did not have the time as needed to get a retest done ASAP. I have included a video link below, it is in German and with this it will help, it is not difficult at all just that some parts are a slight pain but with basic tools it can be done. It took me about 3.5 hours to complete and that from start to finish (tools away etc...) and this was my first attempt at it. If you have access to car ramp then will a little more easier but if not and have a trolley jack and axel stands then it can be done.

    But before you start make sure you are happy with all safety factors first, spend some time looking at what you will be doing and make sure !! So let’s start then:


    1.. Remove plastic engine cover

    2.. Remove windscreen wipers, scuttle panel and plastic panel (this plastic panel sits underneath the scuttle panel and is held in by 4 bolts)

    3.. Remove the turbo inlet aluminium pipe and disconnect from the rubber connecting tubing. IMPORTANT, put a clean, dust free rag into the turbo inlet to protect and stop any debris going inside.

    4.. Undo and remove the Turbo heat-shield 3x10mm bolts, (two at front and one at the rear), for the rear one just take your time and you need a ring spanner for this one. Then slide the heat-shield cover over the Turbo-Inlet and this will reveal the 4 exhaust bolts that secure the CAT to the turbo.

    5.. You can see two bolts very easy. Then there are two more, one at the front and one at the rear, these two are not too bad to remove just take your time. For all these you will need a small socket extension bar, mine is roughly about 9ins, it was tad long as it was very close to the Air-Con pipe-work so I am going to try and find a smaller one. But anyway what I did was to remove the rear nut and the front nut in total and then just slackened off the two top nuts at the top so they can be removed later at the last stage.

    6.. Unscrew and remove the top Lambda sensor of the CAT on the right-hand-side, protect the tip/sensor so I just put it inside a sandwich bag and tucked it to one side out the way.

    7.. Put the car in gear, I used second gear then chock the rear wheels with wheel chock’s/bricks etc… that is in front of the rear wheels and one in front of the passenger side wheel. Using a trolley jack, raise the driver’s side and secure on axel stand. I raised it high enough for me slide under the car comfortably from the front. Once secured I slid underneath from the front and used another axel stand and roughly placed it under the car for safety on the sub frame – so basically had the trolley jack, one axel stand and another final axel stand snug fitted – just in case.

    8.. Remove the driver’s side wheel, this will reveal the second Lambda sensor on the left hand side. Unscrew this and as before put sensor is a sandwich bag and secure to one side.

    9.. Slide under the car, disconnect the secondary cat connection to the Primary CAT. This is on a flexible exhaust section so just place to one side, it will drop anyway so just be careful.

    10.. Unbolt and remove the engine mount to the left hand side of the CAT (you will see it, aluminium in colour), it has 4 bolts. One at the bottom and two at the top, one of the top ones you can see very easy but the second one sits just below it and then finally remove the long bolt that screws through a rubber mount to the engine - you need to remove this engine mount as you will have great difficulty getting the CAT out otherwise.

    11.. Securing the base of the CAT to the chassis is a plate, 2 bolts to the Chassis and 2 bolts to the bottom of the CAT - remove these as it will make it easier to remove the CAT later.

    12.. Finally from the top of the engine unscrew the final two nuts that were holding the CAT onto the turbo exhaust.

    13.. Slide back underneath the front of the car and remove the CAT, you will see it will be just hanging on the turbo bolts - just unhook it and slide the CAT out.


    The fitting is just reverse, all I say about the Lambda sensors are this. I could not figure out how to unclip them from the plugs/connectors so when you come to refit these back then what I did was to turn the sensors anti clockwise about 6 odd turns so when you come to refit/screw them both back in then this winding will undo - so basically you’re not crossing/twisting the connecting cabling on re-insertion of the Lambda sensors.

    I still had the original CAT with the compression gasket fitted, in theory it should be replaced but as long as you tighten the nuts up on the turbo-side you should be ok. The gasket connecting to the Secondary CAT was in good condition so again I reused this as well.

    The video link is here below and suggest you just watch it first then read through the above, if you understand German then your laughing… He didn’t remove the scuttle panel, also he removed one of the turbo nuts from below - I found what I did more easier, it may have took a little longer but then I saved a few scraped knuckles etc…

    https://www.youtube.com/watch?v=YcCOmwmSEzg
    Last edited by Astra_VXR; 12th March 2017 at 12:17 PM.

  2. #2
    VXRed vocky's Avatar
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    5th April 2015
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    who mapped your car or should I say who mapped it bad ?

  3. #3
    VXRed
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    29th September 2014
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    Its not mapped bad fella, done to stage 4. Its always been a bit of a grey area really with the Secondary CAT, it might be the case that mine has gone but have also heard that a few other who have left there secondary in have failed also.

    TBH I wouldn't say "Mapped Bad" unless you have experience or can back that statement up. At the end of the day keep your primary just-in-case

  4. #4
    VXRed vocky's Avatar
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    stage 4 will be the reason then, once you get past a certain point tuning an engine it's damn hard to get emissions good enough for the MOT

  5. #5
    VXRed
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    Your probably right fella, TBH I don't know. I knew there might be an issue with the MoT side, but anyway I just did this how-to-guide above as no one seemed to have done one before and thought it might be a good idea.

    I will probably put the Nortech back in soon but also am toying with the idea of replacing the secondary CAT with a sport CAT. Have seen somewhere that Nortech do one with an HJS secondary CAT.

  6. #6
    VXRed vocky's Avatar
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    if you said stage 1 it would have been the map, but stage 4 means it's quite difficult to get the fuelling right for the mot and produce good power. I am in the same boat with my other car.

    Replacing the secondary cat with a decent cat might be a good idea.

    HJS cats are certainly one of the very best you can get, I have one sat on the bench for my other car but it might end up on my astra instead.

  7. #7
    VXR enough John w's Avatar
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    5th January 2014
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    Good write up John 👍👍


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  8. #8
    VXRed Klystron's Avatar
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    I have a Nortech 2nd catpipe with the HJS sports cat and a 1st de-cat pipe, I was told it will pass the MOT. Well I will find out in May.
    I was also told that I could not go to stage 4 with a sports cat fitted, as there would be too much back pressure. So when you say stage 4 is that with a turbo change?
    Also a bottle of Cataclean could help.

  9. #9
    VXRed
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    Yes mate, had the Hybrid fitted as well. If I was you and would be interested and not sure how much an emission test would cost on the fly, but worth a bash mate before MoT in May, it just saves the hassles.... The only note I have on the test is that the CO2 is MAX 0.2 and mine was on the fast Idle @ 2700 rpm but normal idle it was well under. All other tests on emission fly past...

    It will pass the emissions mate but if the inspector sticks to the rules it has to have 2 CAT's in, that's the problem. But mine was ok to be fair they did try a few times but the CO was out

    Where did you get your HJS from mate and how much if I can ask please.
    Last edited by Astra_VXR; 12th March 2017 at 07:21 PM.

  10. #10
    VXRed
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    Cheers John, I can tell you was a tad nervous when I started lol.. but once you start it's not that bad mate

    Quote Originally Posted by John w View Post
    Good write up John 👍👍


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