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Fuel Pulse Width

EFI Tuning Fundamentals

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Quite an academic / theoretical question... obvious if you know...

When the injectors are told by the ECU to "fire", is a single trigger sent to the injector which then keeps it open for the desired pulse width? After this period, it shuts and waits until it's that cylinders 'turn' again. (this is what I assume to be the case)

Or, is there some form of pulsing going on during the opening? And if so, at what frequency would this be?

Ignoring peak & hold / saturated / voltage configuration - just the essence of the digital signal. As above, my assumption is that physically we want the injector to open, stay open, then shut once per cylinder event.



Most of the time there will be a single pulse per injection event, especially on port injected (PI) engines. Some PI ECU's will allow for extra injection pulses during a single cycle, usually to make up fuel during a large transient event if it can be done within the injection timing window.

Direct Injection (DI) gasoline engines typically only do a single injection event per cycle as well, but they have the option to do injection events at other points of the cycle for catalyst burnoff or other reasons.

DI Diesel (also known as Common Rail) will do multiple pulses per cycle to promote combustion and reduce noise and emissions.

Thanks for the detailed answer! Much appreciated!

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