Fire up and Step on gas

Fire up verb - To rouse to strong feeling or action.

Step on gas and fire up are semantically related in hurry topic. In some cases you can use "Step on gas" instead a verb "Fire up", when it comes to topics like timing.

Fire up and step on gas are semantically related in moving topic. Sometimes you can use "Fire up" instead a verb phrase "Step on gas", if it concerns topics such as hurry, timing.