Can anyone help me with this one pls?
I had my mot done on my 95 ford fiesta at the start of April and amongst other things, the cat had to be replaced. Since then there is often a really bad smell of rotten eggs, not all the time but often. I've tried to keep track of when the smell appears and it seems to be when I've finished going up a hill or it can ust be whenever.
Does anyone have any idea, surely a new cat shouldnt smell like this?

It'll be sulphur that is the smell of rotten eggs but I'm no mechanic so have no idea where it might be coming from. Sorry.

I think sulphur build up usually causes the rotten eggs smell. I think long runs that make the Cat get hot usually clear this up.
Edit: Lucy beat me to it ;)

I never had it on the old one though, is it smelling like this because its new?

It could be the fuel/air mixture too, maybe its burning rich. It sometimes happens when unburnt fuel with trace elements of sulphur pollutes the cat. It should get better with time.

Its ever since I had this new one put in though, surely that should affect fuel/air mix. Does anyone know if its damaging anything because of the smell and whether I should go back to the garage?

It's your catalytic converter. Yes, it is because it's new. After a few long runs, the smell should go away.
:thumbsup:

Changes in engine load and fuel/air mixture would be correspond to your hillclimbing Susa.