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Injector Duty Cycle
Posted: Wed Nov 21, 2007 4:19 am
by Trump
This may seem like a dumb question but I have been unable to find the answer.
Is the duty cycle expressed as a percentage of time the injector is activated.
If so, how can I get a duty cycle of over 100%
Posted: Wed Nov 21, 2007 6:03 am
by efahl
Yup, dumb question. Next!
Just kidding. I think it's in the FAQ, but the reported duty cycle is "commanded" and not the physical duty cycle. For example, say that MS runs through its calcs and comes up with a 12 ms pulse width, but that the engine is running at an RPM with 10 ms cycle time. This would result in a reported 120% duty cycle, which although not physically possible, is still very diagnostic in that you know your injectors are too small, or that your injection pattern is wrong, or fueling values are incorrect by some quantifiable amount.
Eric
Posted: Wed Nov 21, 2007 6:30 pm
by Trump
efahl
Thanks. I revisited FAQ and could not find the info required.
Lets see if I have got this correct.
If I show a Duty Cycle of 110% at a particular RPM/kPa, Then the injector is 'on' 100% of the time and is in fact underfueling by 10% (not taking into account the fact that it should be kept below about 80%)
Posted: Thu Nov 22, 2007 8:34 am
by efahl
It might be underfueled by 10%, or maybe the tune is 10+% too rich, you need to figure that out. Early on in tuning a motor it is not unusual to have things way too rich resulting in duty cycles over 100%; these will go away as soon as you get the tune in the ballpark, assuming you did the up-front math and have properly sized injectors.
Eric