Strange missfire
 

Hi All, i seem to have a strange intermittent missfire, only does it now and then and at around 6k, when it does it the rpm needle drops quickly, it only missfires once or twice then carry's on. What supplies the signal to the rpm needle, other than ECU where does it get the info from? All coil packs are new but i think this is a problem at source.

Crank sensor is new and cam sensor seems fine.

Thanks.