Yo.

I've got a 1997 1.4l Mk. 3 Astra, which is currently giving some lovely rattling and, on the over-run, feathery noises from the catalytic converter. I think it's fairly safe to deduce from this that, in a 13-year old car, it's dead.

I found a possible replacement, but in honesty - is it necessary?

What do emissions tests actually test for? And, given that the engine emissions tests for the last few years have been excellent, what is my car going to be chucking out the back? Is it worth removing the cat and replacing it with just a straight-through pipe, or is that just asking for MOT failure?

Opinions please.


Weasel

They will have a set of emissions results for your specific car model and if it will fail if you remove the cat.

The cat may not be completely dead so I would have the test first and then only replace it if it does fail. Most test centres offer a two week retest.

As said it will fail without a cat, it will be tested as if it still had one.

had to replace mine first month I bought my car cost me a measly £400

Aye, that's the plan. It's just a lot of money I don't have.

Bratty: £400 for a cat!?

This is Bratty we're talking about, his 'cat' and 'car' probably look like this:

Yeah, you'll need a cat as it's a post '92 car.
My understanding is that if your car is pre-'92 you can de-cat it - so long as it still passes the emissions regulation for that year.
Which basically means getting your engine good and warmed up prior to the test. Don't take it in cold.
AFAIK, IANAL, YMMV.

Are you sure it's teh CC? My Mum's exhaust pipe started rattling and it turned out to be a product ID tag that was welded to the pipe. The weld at one end had broken and the vibration was causing the rattle. The bloke just ripped it off, problem solved.

Bugger.

Pretty certain. There's a few rattles on her - manifold heatshield, and so on - but this one is pretty loud. That in itself, I suspect, is just a bracket or something come loose. The feathery noise on the over-run coming from the same area is what worries me. Doesn't help that my car sits so low to the ground I really can't get under to poke about. :-/ Need to get it checked out, but preparing for the worst.

common problem is the heat shields come loose or the rubber holding them perish, check it out first it might save you some moolah

Getting the engine warm before the test is all well and good, as long as the emissions are tested before the rest of the test.
The MOT station I worked in we did it after main test, but a probe is put in dipstick tube to measure temp of oil, and has to 80c for the test so is brought up to that anyway.