The disclosure provide a
sulfur-free and
halogen-free synergistic additive concentrate for a fuel injected engine. The additive concentrate includes (a) an alkoxylated
quaternary ammonium salt of the formula (R1)nN[(R2O)xH]m, wherein R1 contains from 1 to 25 carbon atoms, R2 contains from 1 to 4 carbon atoms, n and m are each integers from 1 to 3, provided n+m=4, and x is an integer of from 1 to 5; and (b) a material containing a
hydrogen-bonding group other than an
alkyl hydroxyl group selected from the group consisting of a hydrocarbyl acid; hydrocarbyl polyacid; hydrocarbyl substituted hydroxybenzene; hydrocarbyl substituted succinic diamide, acid /
amide, diacid, diester, ester / acid,
amide / ester,
imide; aminotriazole, and mixtures thereof, wherein the hydrocarbyl
substituent has a number average molecular weight of from about 100 to about 1500, and wherein a weight ratio of (a) to (b) in the additive ranges from about 1:5 to about 1:1.