FAQ: What do the terms “static” and “duty cycle” mean?

ERIKC Answer:An injector in an engine turns on and off very quickly to control the amount of fuel delivered. The amount of time an injector is turned on and delivering fuel is known as the duty cycle. This is measured as a percent, so 50% duty cycle indicates that the injector is held open and held closed for an equal amount of time. When the engine needs more fuel, the time that the injector stays on (its duty cycle) increases so that more fuel can flow into the engine. If an injector stays on all the time, it is said to be static (wide open, or 100% duty cycle). Injectors should not go static in a running engine. If an injector is static in a running engine (open 100% of the time), that injector is no longer able to control fuel delivery. This could be an indication that the injector is too small for the needs of the engine. Injector duty cycle should usually not exceed 80% in a running engine at any time.

FAQ: Can you alter injectors to increase their static flow rates?

ERIKC Answer:Absolutely not. It is sometimes possible to increase an injector’s static flow rate at a given pressure by machining or enlarging the pintle or internal passages of the injector. However, this procedure is usually not a good idea! A fuel injector cycles on and off thousands of times per minute to feed an engine the proper amount of fuel. Because of this, the electromagnetic coil and pintle of an injector are very carefully matched to one another. Modifying the pintle or other portions of the injector may cause it to flow more fuel at its limits (wide open or statically), but at lower engine speeds the injector will be extremely inconsistent. This creates drivability problems, idle fluctuations, higher emissions, rich/lean conditions, etc. We have performed extensive laboratory tests on many modified injectors and have yet to find one that performs as well as an unmodified injector of the same capacity.