A diesel fuel composition comprising:(a) a major portion of a diesel fuel, and(b) a minor amount, as a diesel fuel injector detergent additive, of a Mannich coupled product of bis-polyisobutylene succinimide of an amine, prepared by:(i) reacting an alkenyl succinimide acid anhydride with an amine to form a bis-succinimide;(ii) treating the bis-succinimide with nonylphenol in the presence of an aldehyde to form a Mannich phenol coupled bis-succinimide product; and(iii) recovering the product Mannich phenol coupled bis-succinimide.