Method for improved performance in fuel injected engines

A method for improving performance of fuel injectors, and a method for cleaning fuel injectors for an internal combustion engine. The methods include operating the engine on a fuel composition comprising a major amount of fuel and from about 1 to about 200 ppm by weight based on a total weight of the fuel of a reaction product of (i) a hydrocarbyl substituted compound containing at least one tertiary amino group and (ii) a halogen substituted C2-C8 carboxylic acid, ester, amide, or salt thereof, wherein the reaction product as made is substantially devoid of free anion species.