How does a high concentration of carbon monoxide affect miles per gallon performance?

A high concentration of carbon monoxide in vehicle emissions is indicative of incomplete combustion of fuel. This incomplete combustion often occurs when there is an insufficient amount of oxygen in the combustion chamber, leading to an inefficient burn of the fuel. As a result, the engine has to work harder to produce the same amount of power, which can lead to increased fuel consumption.

Consequently, when carbon monoxide levels are elevated, it typically correlates with a decrease in fuel efficiency, meaning that the vehicle will consume more fuel for a given distance traveled, thus decreasing the miles per gallon performance. Therefore, the relationship between high carbon monoxide concentrations and fuel efficiency is one where higher emissions contribute to lower efficiency.