I got an fiat Punto gen. 2012 1.3 MJT when I was on vacation and I was driving on the motorway and I started accelerating, when it started knocking very loud, I pulled over and when I tried to listen the sound came from cylinder 1 sounds like it's the top of the motor and I can only think og 3 things injector, valve slap, connecting rod bearing. it's a very metallic sound :-( any ideas?