Right Chaps i'll try me best to explain my problem. I recently bought a ford fiesta flame 2004 that has done 30k. The car was driving fine unitl the enigine warning light came on but was not flashing. i took it to a local dealer and couldnt find any faults. about 100 miles later i started to notice a slight misfire in the acceleration when in low revs. after reading a few threads and having the same problem on my other car i took it straight to a ford garage. They told me that the misfire was from a faulty coil pack and because i had been running the car with this fault it had damaged my cat. So to avoid the ridiculous prices i decided to fit the parts myself. From some advice i wanted to wait on a new cat as they are quite expensive and money was tight. i fitted a new coil pack at a cost of 45 quid. The car drove like a dream once more. however after about a week or so the car grinded to a halt with the engine management light flashing and the car had no power. i managed to get it home and put my old coil pack back on which allowed me to drive the car again with only a slight misfire rather than no power at all with the new one. sooooooooooo, could the faulty cat cause the new coil pack to completely be knackered or is the coil pack i bought not good enough as it was only cheap? or could it have just been a dodgy spark plug that cause the first and second coil pack to fail. but if it was the spark plug why is there such a massive difference in performance in the 2 coil packs i have??? PLEASE HELP ME ANY ADVICE WELCOME!!!

Did you disconnect the battery for a min of 30mins when you changed the parts?

Sometimes you need to do this to enable the ECU to re-learn the car with the new parts.

Sounds like your new coil pack is iffy. I cant see what the CAT has got to do with anything. I would try another coil pack and change your plugs and leads if they havent been changed recently.

I had a similar issue with the wifes SportKA. It was missing, so I replaced the leads and plugs. It was still missing, so I changed the coil pack, still no difference. After hours of pulling my hair out, it turned out to be one of the new plugs wasn't firing. I was not happy with all the time I had waisted, when my first thought had been right all along.

I disconnected the battery after installing the new coil pack to try and turn off my engine warning light but that didnt work. I am going to try new leads, plugs. as for the coil pack it will have to be a new one again as eurocarparts wont let me return the dodgy coil pack they gave me. Think im going to spend a little more on one this time too. If this one fails again then i am clueless as to what the issue can be

Let us know how you get on.