Hello,

I bought a 1.4 Fiesta Zetec yesterday from a car auction as a cheap run around. Im not to hot when it comes to Fords but know my way around an engine.

Its done 80k miles and seems to be all OK apart from a low rev misfire. At idle it is a little lumpy and when the accellerator is slowly applied the misfire seems to get worse up to around 2k and the car judders. Over 2k it dont seem as bad. When driving you can feel the missfire all the time if you look for it, but at lower revs it is more noticable. Pulling away can be a bit of a pain and requires more revs than it should.

I removed the leads one by one with the engine running and one didnt make any difference. It the 3rd cylinder from the left. I took out the spark plug and it was black and wet. To check the plug, I cleaned it up and put the wet plug in another cylinder and the good plug from that cylinder into the cylinder that wasnt firing. The wet plug fired fine in the good cylinder, but the good plug in the misfiring cylinder didnt make any difference. To test the leads I changed the leads over which again didnt make any difference. I thought that the injector may be faulty so swapped them, again, no difference.

I am now worried that I have a problem with the valves or rings on one cylinder. I will do a compression check if I get time tody on all the cylinders.

I have read that the coil pack can cause a low rev misfire, but when I tested the leads yesterday there was a spark jumping between each lead and the coil pack when I removed them one by one so assumed the coil pack was ok?

Can anyone suggest anything else it could be? Im worried I have bought a lemon :(

Thanks,

Mabbo

the symptoms does sound like a coil pack problem,allthough you get a spark it may only be a weak one, they realy need testing with a coil pack tester.

the symptoms does sound like a coil pack problem,allthough you get a spark it may only be a weak one, they realy need testing with a coil pack tester.

i agree totally with that.

i had similar issues with my focus, i checked to see if i was getting spark - which i was, so i replaced the coil pack and plugs and its been fine although...

after a year it started again so i replaced the coil pack and this failed after 6 weeks or so, i replaced it again but changed the leads and plugs also and its been spot on now for 4 months (touch wood)

i agree totally with that.

i had similar issues with my focus, i checked to see if i was getting spark - which i was, so i replaced the coil pack and plugs and its been fine although...

after a year it started again so i replaced the coil pack and this failed after 6 weeks or so, i replaced it again but changed the leads and plugs also and its been spot on now for 4 months (touch wood)

if they are black and wet then its likely oil leaking past the guides or piston rings which will cause a misfire and continue to untipl you have it repaired changing plugs wont help nor will a new coil pack the oil leaking past the rings is the likely cause

Thanks for the replys.

Well, I have tried a new lead and it made no difference but I dont think its the coil pack because I have a strong spark from the lead to the plug when I remove it.

I done a quick compression test with a Gunson cylinder pressure tester. The tool wouldnt fit in the plug hole so I pushed it down and held it there as best as I could. Not ideal I know but, when I held it in number 3 cylinder and had someone crank the engine there was no pressure at all compared to when I held the tool in the number 2 plug hole. I could feel the compression from the number 2 cylinder pushing the tool upwards.

I done an engine flush and oil change incase there was a sticky valve but there was no improvement.