Ford Focus misfire-loss of power.

It may need plugs if the coil packs been faulty.

Check there is no water in plug wells , common fault which can cause spark to short .

Thanks for your answer, it's had new plugs & leads, when I'm in my drive, it will rev fine, as soon as I drive it coughs & splitters, someone suggested I change the fuel filter, I will do that and if that doesn't work they said it could be a valve, quite a big job to say the least.I would be grateful for any more suggestions.
Thanks in advance..
Steve. .

Thanks for your answer, it's had new plugs & leads, when I'm in my drive, it will rev fine, as soon as I drive it coughs & splitters, someone suggested I change the fuel filter, I will do that and if that doesn't work they said it could be a valve, quite a big job to say the least.I would be grateful for any more suggestions.
Thanks in advance..
Steve. .

Carry out a compression test and it will tell you if valves o.k or not .You wont know if timing belt has been replaced if you just got it . Dont know the mileage but it would be due replacing going by the year .The belt can stretch / wear and jump , throwing timing out .Cant remember what years and engines on the Focus which were common for valve problems , eventually dropping a valve on I think no4 cyl .Obviously yours has not got to that stage just now .

i also have 1.6 focus 51 plate it missfires only when engine is fully at normal running temp no engine light comes on and there is interfierence on the radio when missfire occures engine is quiet and starts first time on a morning?