I posted last week that the beloved Mk2 8v Punto had failed on emissions and a blowing exhaust back box. I am happy to report that after fitting a new back box, adding some fuel additive to a tank of Shell, and some motorway miles, today it passed! It was interesting to watch the CO reading drop slowly at first, then plummet as the cat got properly hot. Result!
I must remember that this is a runabout car and it needs a good blast to clean things up before an MOT.

It needs a regular good run to avoid damaging the cat when it does get properly hot..

Why is that?

The catalytic converter needs to be hot to work properly. If it never reaches full temperature, unburnt hydrocarbons will build up and gradually block the ceramic matrix inside the casing.

When it does get hot enough, that gunk should be burnt off. But if there is too much it might permanently block the matrix or make so much heat it causes damage.

WhiteSei said:

The catalytic converter needs to be hot to work properly. If it never reaches full temperature, unburnt hydrocarbons will build up and gradually block the ceramic matrix inside the casing.

When it does get hot enough, that gunk should be burnt off. But if there is too much it might permanently block the matrix or make so much heat it causes damage.

Click to expand...

Any idea how far you have to go to get it hot?

I would go at least 30 miles at motorway speeds at least 1x per month. Just revving the engine wont be enough it needs the large gas flow from when the engine is working.

WhiteSei said:

I would go at least 30 miles at motorway speeds at least 1x per month. Just revving the engine wont be enough it needs the large gas flow from when the engine is working.

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OK. Thanks for the advice.

WhiteSei said:

The catalytic converter needs to be hot to work properly. If it never reaches full temperature, unburnt hydrocarbons will build up and gradually block the ceramic matrix inside the casing.

When it does get hot enough, that gunk should be burnt off. But if there is too much it might permanently block the matrix or make so much heat it causes damage.

Click to expand...

This explains why my last car (my first car) a Vauxhall Corsa Mk1 had to have a hole drilled in the bottom of the CAT because as i was a bit new to driving (and didnt trust the old Corsa on the Motorway ! ) i was always doing short journeys .