I've got a 75SX and every blue moon it will not start. It will turnover but will not fire. I can bump start it when this happens and it will be fine but every now and then it will not start. Any ideas what the issue is?

when was it last serviced?
also its getting colder now and time for batteries to die, so there might not be enough power to turn it over fast enough and have electric left for fuel and ignition system

mine has this problem occasionally. I just hit the multifunction relay and it works again. You'll find this under the black cover at the back of the engine bay (a white block about 2"x1")

If that sorts the problem, get a replacement from a scrappy/ fiat dealer.

can this cause running problems?
As my 75 is juddering and sometimes cutting out