Right Chaps i'll try me best to explain my problem. I have a ford fiesta flame 1.4 2005. 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. 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 thought this may have been a dodgy coil pack so just got another one and once more the car drove fine. but same again after a a few hundred miles the engine light came on with no power in acceleration. 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 ones. sooooooooooo, are the coil packs i am buying not good enough as they were only cheap? or could it have just be a dodgy spark plug that cause the 3 coil packs to fail. but if it was a spark plug why is there such a massive difference in performance in the 3 coil packs i have??? Would my old coil pack react different to a dodgy lead or spark plug to the cheaper new coil packs? PLEASE HELP ME ANY ADVICE WELCOME!!!

have you tried changing the spark plugs AND leads?

I agree it could be spark pugs or leads , if not worth checking the lambda sensor as it may be covered in unburnt fuel from the missfire.

ok so replaced the leads and plugs and although there is an improvement the car is very sluggish getting up to speed and is slow to respond when asking to do a little more e.g. going uphill or accelerate a bit quicker. so i will try replace the lambda sensor. am i right in thinking this is the sensor at the back of the engine? if so is it easy to replace? it doesnt look easy to get to? could be a job for a garage and if so what do you reckon the cost will be??

the lamba sensor goes into the exhaust pipe,so look at the exhaust from where it joins the engine and you will see the wires going to the sensor (dont know about the fiesta but some cars have more than one sensor),not sure about the cost.

the lamba sensor goes into the exhaust pipe,so look at the exhaust from where it joins the engine and you will see the wires going to the sensor (dont know about the fiesta but some cars have more than one sensor),not sure about the cost.

At the back of the engine where the exhaust manifold is, there will be a wire going to a sensor screwed into the manfold itself, I believe you will need a 22mm spanner/lambda sensor socket to remove it. ford want upto £130 for this but you can get it for £30 locally and takes 10 mins to change