Low MPG after spark plug change on 1.2 16v

[akimbo-slice]

So as the titles says my MPG has dropped from 39 to 32 immediatly after i changed my spark plugs, as far as im aware they are the correct spark plugs and i didn't under torque them.

Anybody know the reason for this?

Do spark plugs have to 'bed in'?

I did notice some fractures running up the sides of the ceramic on one of the new spark plugs, could this be the fault?

 

[joshhicky]

They could just be bad spark plugs you said one had a crack in it then maybe there producing a weak spark and all of the fuels not burning, but apart from that am not sure mate.

 

[gti6steve]

You fitted a spark plug that had fractures up the ceramic please tell me you didn't

 

[akimbo-slice]

im afraid i did, really didnt think it would be that big of an issue because the fractures were so slight but now i have seen how very foolish i was haha.

Praying that when i open it up again i wont have to spend the rest of my life fishing out bits of spark plug.