Z16Xe Zafira A / Astra G Catalytic Converter Replacement

In principal this is quite a simple job and you don’t really need to be mechanically minded to do this at all, what makes it a pain is rusty nuts ! Be prepared for those rusty nuts from hell ! In this post I will just outline some tips when it comes to replacing the cat for this specific vehicle as it might come in useful for others out there.

So it’s been fifteen years and 65k miles for my Dad’s Zafira, I guess it’s going through the “bits are wearing out” kinda stage. The vehicle has been flawless but in the last year the following have happened:

Exhaust muffler blow – Replaced

Exhaust mid silencer blow – Replaced

Downpipe flex collapse – Replaced

Primary and Secondary o2 sensor failure – Replaced (use genuine NTK/GM/Bosch/Denso or you might get EML issues!)

And now the latest addition: “P0420 – Catalyst System Low Efficiency” ! Eeekk

So this is the best answer I found to removing all the manifold nuts. This is a tool known as a “nut/bolt extractor” and is essentially a sharp spiral teething socket that grips into rusted nuts or bolts and gets them loose ! The ones I went for are the “Irwin Bolt Grip Expansion Set” which has the correct 10mm fitment for the Zafra/Astra G. I would not of got the job done without these they are perfect for this job. It is possible to do the nuts off with a chisel and a hammer but the “Irwin’s” save loads of time and risk of damaging the stud threads.

Would you like to see what happened to the old catalytic converter ? Well here you are, no wonder it wasn’t do it’s job most of the monolith element was gone ! As you can see it is a really chalky colour which is a sign of fatigue and heat damage, 17 years though cannot complain !

There is not much else to mention apart from some tips regarding the new cat. I purchased an “eBay approved cat” costing £100 but there are some differences to note against the OEM GM cat !

Firstly as you can see in the photograph the bottom down pipe connection has bolt holes instead of integrated studs. This is fine apart from the Screws/Nuts supplied are absolute rubbish ! I don’t know what they are but the nuts have weird dipped threads so when you are putting the nuts on they suddenly go extremely tight, and it’s impossible to do laying under the car using a socket in one hand and a spanner in the other !

My advice is ditch the provided Screws/Nuts and pick up the Halfords M8 assortment pack for £3.48 they are perfect for the job and save a lot of hassle !

Also another mention which is unavoidable really but still a bummer and that’s the manifold casting shape. Basically the new one has slightly shallower header branches, if you look carefully on the photo above you will see the far right branch is a fatter shape and this makes the far right bottom nut really damn hard to fit ! The only way I could get it done was to remove the oil filter, and even after that it took about half an hour to fit the damn nut with an open end spanner !

So just to conclude this task: