A system for a vehicle includes a voltage measuring module, a second derivative module, a closing period module, and an injector driver module. The voltage measuring module measures first and second voltages at first and second electrical connectors of a fuel injector that injects fuel directly into a cylinder of an engine. The second derivative module determines a second-order derivative of a difference between the first and second voltages. The closing period module determines a closing period of the fuel injector based on the second-order derivative of the difference. The injector driver module selectively adjusts closing of the fuel injector based on the closing period.