Focus misfiring

I have a 2004 Ford Focus 1.6LX, petrol engine, manual gear change. The other day I noticed misfiring when depressing the accelerator and then noticed that the engine warning light was on. I took it to the garage and they said it was something to do with emissions and replaced the hergon (hercon??) centre (???). There was still a fault, so they replaced the whole catalytic converter. This did not solve the problem. Any ideas? The garage is stumped. On an old Rover I had a similar problem and it was something to do with the flywheel senser.

What you need to do is find out exactly what the error codes were that were associated with the engine light. Their format is P1234 - post the exact codes.

I have never heard of anything at all like a"hergon/hercon centre" - but I am in the US and you are probably not (Britain?) so terms may differ. By what you describe I’d say they’ve been messing with oxygen sensors since those are the things wrapped up in cat converter operation. All the more reason to have the actual error codes.

You might also start to wonder about the shop you are using. Some shops try to fix things just by guessing. This can work and save some time and money - but it often doesn’t work and costs more time and money.

Thanks for that - how do I access the error codes? Yeah, I am in Britain.

If you have invoices from the shop the codes might have been written there. If not, you could call the shop to see if they have a record. Other than that you’d need to either get a code reader (OBD-2 for on board diagnostics) or have someone with a code reader hook it up.

I don’t know what the options are in Britain. In the US large auto parts chain stores will read error codes for free - or one can buy very basic code readers for $50-60.