Hi all, had a misfire on my 2001 fiesta zetec s when cold. Expected it to be ignition based, but borrowed a compression tester to check nothing inside was at fault. When I removed the plugs I found this-


Only 2 of the plugs were cracked, with this being the worse one, the other hadn't opened up. On replacing the plugs (to go get some new ones) the car was missing all over the place, and running on 2 cylinders if I gave it anything more than 1/4 throttle. Now, a new set of plugs solved this, but, as the 'old' ones were only about a month old, it's made me worry that something is amiss. Any ideas what's caused the plugs to do this?
Thanks, Sam.

 

i would say that was done on fitting or removal as there quite fragile really.

 

I took care fitting and removing, and they weren't cracked when I fitted them, that's for sure.

 

Did you overtighten them? Your suppose to do them up as tight as you can by hand and normally 1/4 of a turn on the ratchet to pinch them up. looks as tho they may have been done up too tight and the twisting forces have put a hairline fracture in the ceramic part which after its got hot and cold a few times has split and you see what you have above?

 

Could have been damaged in box and hot and cold starts weakend them more ?

 

Could have been overtightened I guess, never do them up silly tight(both my wrists are fucked from DH riding anyway, so can't put a massive amount of pressure on a ratchet!), but I guess just a touch too much may have done it. Just strange that only 2 have done it, and 2 are totally fine. Also that fact they're only a month old, and I've replaced plugs many times before with no trouble. :/