Fuel injection control system for internal combustion engine

A fuel injection control system for an internal combustion engine, which is capable of properly performing instantaneous injection, thereby capable of attaining excellent exhaust emissions at the start of the engine, and performing prompt engine starting. In the fuel injection control system, the instantaneous injection that injects fuel to a predetermined cylinder is executed immediately when it is determined that a predetermined condition is satisfied after cranking of the engine is started. A leaning influence ratio which is a ratio of a time period during which vaporized fuel supplied to the predetermined cylinder becomes lean to a instantaneous injection time period which is a time period over which fuel is injected by the instantaneous injection is estimated. A threshold value is set based on temperature of the engine. When the leaning influence ratio is larger than the threshold value, the instantaneous injection is inhibited.