1.
If you fire up a machine, you switch it on.
Put on a helmet, fire up your engine and head out on the open road.
PHRASAL VERB : V P n (not pron) , also V n P
2.
If you fire someone up , you make them feel very enthusiastic or motivated.
The president knows his task is to fire up the delegates.
PHRASAL VERB : V P n (not pron) , also V n P