cav551:
You have had at least half a dozen replies already with various possibilities. You have a choice to make: either start guessing which of the suggestions may be what is wrong and work your way through them, throwing parts at it as an expensive elimination procedure; or follow a logical diagnostic fault finding trail. This would be the same whether you have an electronic engine or an older mechanical version. Alternatively leave the investigations to someone with the experience and necessary test equipment.
I wouldn’t waste any time I just plug it in ,then again it’s a Cat they do smoke 