Help! I just had a restless nights sleep as think I may have made the worst buying decision in in 35 yrs driving,i brought a 2003 1.8 zetec petrol focus with a known misfire for £600,after buying a new coil pack,leads & sparks plugs I still had the misfire,a local garage confirmed No. 1 cyl was low on compression & found the burnt out valve found when it was stripped down,after replacing the valve it still had low compression & the misfire,its now had all the rings replaced so compession is like new etc,to cut a long story short they just about to give up on it as they just spent a day on it,swapping injectors,leads,coilpack,plugs etc,at the moment they got the manifold off looking for cracks etc but even after getting the bosses friend in to help they at a loss to find the problem its always No. 1 cyl that's give the misfire,i dont think I have any choice now but have it to put it back together & drive it,,i sure someone has had this problem before but I not sure its worth spending any more on it,it I do get to the bottom of it I will let you all know in the hope it will save someone else the expense ive had,cheers Steve

Have a read and see if anything leaps out at you-

http://www.engine-misfire.com/

are we talking a permanent misfire or random, does it miss at idle only, or throughout the rev range

if permanent..

well if you take the 4 stroke process one by one

fuel....injectors have been swapped, but is no 1 receiving a signal to open

compression...now up to level so can be eliminated..so long as compression is strong and reaches its reading within 3-4 strokes max, and valves are actually opening, could be a problem with cam for eg...

ignition..new leads etc, but is coil pack sending a spark to no 1 at correct time, sometimes the ecu can fail...get a set of plug testers that fit between lead and plug, i know plugs are recessed but should still be visable

exhaust...only reason i can think for a problem here, if compression is good, would be a blockage in manifold at no 1 or valve isnt opening

the pcm diodes fail causing a misfire that cant be cured the pcm would have to be removed and sent away for testing and repair bba reman do them but its around £250