Fuel injectors are the valves that regulate the amount of fuel that enters the engine of a vehicle. During the normal operation of an engine the fuel injector temporarily opens allowing the fuel to enter the engine. The amount of time that the fuel injector stays open is referred to as the injector pulse width (IPW). Fuel injector duty cycle is a term used to describe the length of time each individual fuel injector remains open relative to the amount of time that it is closed. For example if, during each of the fuel injector's pulses, the injector is open for 75 milliseconds and closed for 25 milliseconds, the injector duty cycle (IDC) would be 75%. This is because the injector remains open for 75% percent of the time that it takes to complete one pulse. Knowing a fuel injector's duty cycle is important because it can help you determine if the injector is still functioning correctly and if your injector is the appropriate size.
Choose a fuel injector to test.
Run the vehicle's engine at a specific number of revolutions per minute (RPM) and determine the chosen fuel injector's injector pulse width (IPW) at this speed. (This is best done by a professional who has access to a datalogger.)
Click on the injector duty cycle calculator in the resources section of this article.
Enter the information from step two (both the RPM and the IPW) into the appropriate text boxes on the Web page that pops up.
Click "Calculate". The injector duty cycle percentage will then be displayed in the yellow text field.
