How To….. Remove the PrePre-cat on a 2.2 (Z22SE) Astra-Sport Disclaimer - Please note that this is a guide only and Astra-Sport take NO responsibility for any damaged caused to yourself or vehicle whilst using this guide. If you are unsure how to do something leave it to the professionals. Your Insurance and warranty might be invalidated if this modification is done. Why do this Mod? The pre-cat is only there to control emissions on start-up from cold, until the main cat gets up to working temperature, after which time the main cat does all the emission control work and the precat just becomes a needless restriction. The MOT emission test must be done with the car at normal operating temperature – so removal of the pre-cat will not cause the car to fail the test, nor will it render it illegal Step 1 - Removing the heat shield Working from inside the engine bay, remove the engine cover to gain access to the back of the engine (exhaust manifold). Using a 10mm spanner, undo the three bolts that hold the lower heat shield onto the manifold as shown in the diagram (circled blue). Once all three are out, gently remove the heat shield from the retaining clip (circled red). Step 2 - Jack the front of the car up and place securely on axle stands or ramps. Remove ignition key UNDER NO CIRCUMSTANCES RE-INSERT THE IGNITION KEY UNTIL THE JOB IS FINISHED.
Thanks to Ffoeg for the ‘How To’
Step 3 - Removing the cat assembly •
Working under the car and using a socket and extension bars undo the three nuts securing the down-pipe to the manifold.
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Using an open ended spanner, carefully remove the 2 oxygen sensors – one in front of the main cat and one behind. These will probably be rusted tight, but with a soaking in WD40 and gentle persuasion with a mallet on the end of the spanner they should come undone. Once out, just let them dangle, but be careful not to damage them.
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Remove bolt on the clamp between the cat and centre section (shown below) – this will probably be rusted tight, so again use plenty of WD40 and a bit of force. You may be lucky and it will come undone relatively easily, but if not, either cut or grind off the bolt and replace with a new one on reassembly. Once off, use a large screw driver to lever open the clamp slightly.
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Give the exhaust joint a good dousing with WD40, and remove the two rubber hangers on the front of the centre section to allow the cat will now drop down slightly. The cat assembly will be a tight (rusted) fit in the centre section, so a lot a lot of twisting and pulling is required to separate the two parts. Keep dousing, twisting back and forth and pulling and it will eventually come off. Thanks to Ffoeg for the ‘How To’
Step 4 – Removing the pre-cat Lay the cat assembly down with the pre-cat on the right – this is the best position to minimise any debris falling down the pipe and entering (clogging) the main cat. Drill a series of closely spaced 4-6mm holes around the edge of the pre-cat (as shown below). Use the drill on a low speed and it goes through quite easily – whereas a fast speed just overheats the bit and blunts it very quickly. Periodically inspect the drill and remove any accumulated debris from the tip with a screwdriver – the drill will be very hot, hot so be careful and patient. Once you’ve completed a full circuit of holes, change to a large drill (6-8mm) bit and re-drill alternate holes, once again ensuring you go straight through the pre-cat - this should break through the sides of the small holes and enable the pre-cat matrix to be removed. However some teasing out of material with long-nose pliers/screwdrivers/chisels may be required Using an old ¼inch wood chisel or similar, carefully scrape away any remaining material from the edge of the pipe, and then finally give it a quick once over with some coarse emery cloth to remove the last of the material (a Dremel and small grinding wheel will speed this stage up). The finished article should look like the photo below – clean and smooth. Once all trace of the pre-cat is removed from the end of the pipe, upend the cat assembly and tap/shake firmly to dislodge any material from the pipe. Finally, cover up the front oxygen sensor holes and give the pipe a good vacuuming out to remove all traces of dust and debris – repeat the shaking, tapping and vacuuming process until all debris is clear. Step 5 – Reassembly is a reverse of the removal process – but use some copper grease on the manifold, pipe nuts and cat assembly pipe where it enters the centre section. Check alignment of the exhaust before finally tightening up any of the nuts/bolts. That’s it – go for a test drive and feel the difference!! Thanks to Ffoeg for the ‘How To’