The injector duty cycle is the amount of pressure exerted by the fuel injector.

• A. True
• B. False
• C. It measures temperature
• D. It measures flow

Answer: (B)

Injector duty cycle is a timing control, not a pressure value. It represents the fraction of each engine cycle that the injector is energized and spraying fuel. In other words, it’s how long the injector stays open, expressed as a percentage of the cycle time. The pressure at the injector is determined by the fuel rail pressure and the injector design, and stays largely separate from this timing signal. So the statement that duty cycle is the amount of pressure exerted by the injector is not correct.

As fueling demand increases, the ECU increases the duty cycle to keep delivering more fuel; at high demand the duty cycle can approach the maximum, but the actual pressure the injector exerts is still set by rail pressure, not by how long it’s open. Flow is affected by both duty cycle and rail pressure, but duty cycle itself is not a direct measurement of flow or temperature; it’s the control signal that governs fuel delivery.