please help!!!

my wife owns a premacy 1.8 petrol.its just started to misfire at around 3000revs and wont rev over this.it ticks over ok but misfire's like crazy when u put your foot down.i've just changed the sparkplugs but no good.

any ideas??

 

I don't know the Premacy, What kind of engine? model year? mileage? auto or manual transmission? prior history (maintenance and incidents)?
What was the condition of the plugs you replaced? [ whitish-grey = lean mixture, tan= good, sooted = rich mixture, oil fouled, or misfiring].
Do you have a Check Engine light on? (On vehicles having the OBD-II diagnostics, ignition related misfires will set the CEL on; mixture related issues may or may not).
I suggest you start by reading the thread in the Protege forum referenced below and go step by step through the schedule of tasks which will highlight the more or less obvious things to start with, and then we'll take it from there.
The thread is I have a 2000 Mazda Protege, 1.8L with 5 speed manual transmission @ 190,000 kms Beyond this, it is possible that your timing is off. This could be crankshaft sensor related or could be the timing belt is worn out and has jumped.
The other issue producing your symptoms is fuel starvation.
Mazdas have a two stage fuel pressure regime, 33 psi +/- 3 at low power, and 42 psi +/- 3 at high power. If you have a fouled fuel filter, you won't support the high end.
I suggest you do the tender loving care items associated with air intake and ignition first, the get back here with a status update before proceeding further.

 

i'm too late the wife's called a bloke out to look at it on tuesday,but thank you for your helpfull reply.

 

just a quick update,we've had the premacy fixed and the problem was a timing belt adjuster.we were charged 3 hrs labour and had to buy a complete adjuster kit also we had a new timing belt put on,total cost of parts £125....ouch!