running on empty - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
At the end of one's resources, out of money, as in I don't know how much longer we can live this way—we're running on empty with no jobs in sight. This idiom refers to a car running when the gas gauge indicates it is out of fuel. [Second half of 1900s]