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Shot me 3 deer!!!
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Hey all, I was wondering if someone could go into depth w/ duty cycle. I've never really understood it!!
 

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I AM DA FOCI FANATIC
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What exacty do you want to know?
Duty cycle is the amount of time that the fuel injectors are switched on. A duty cycle of 0% means that the injector is not on at all, a duty cycle of 100% means the injector is on constantly. Duty cycle at idle is normally only a few percent, rising as revs or load increases.

Injectors only has a small amount of time to inject fuel into the mixture. So when you are creating more power, you are needing more fuel so the injector will open and stay open longer allowing more fuel into the mixture. Eventually you will get to the point where the injector can not supply enough fuel in the time frame.

This calls for a larger injector which can supply more fuel in a less given time.

So when someone says they are at 70% duty cycle, that means the injector still has 30% left in its cycle.



Also some cars (Not ours) run 100% duty cycle and control the fuel by pressure, but that another story
 

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I AM DA FOCI FANATIC
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3,715 Posts
What exacty do you want to know?
Duty cycle is the amount of time that the fuel injectors are switched on. A duty cycle of 0% means that the injector is not on at all, a duty cycle of 100% means the injector is on constantly. Duty cycle at idle is normally only a few percent, rising as revs or load increases.

Injectors only has a small amount of time to inject fuel into the mixture. So when you are creating more power, you are needing more fuel so the injector will open and stay open longer allowing more fuel into the mixture. Eventually you will get to the point where the injector can not supply enough fuel in the time frame.

This calls for a larger injector which can supply more fuel in a less given time.

So when someone says they are at 70% duty cycle, that means the injector still has 30% left in its cycle.



Also some cars (Not ours) run 100% duty cycle and control the fuel by pressure, but that another story
 

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Dutycycle is how much work an injector is doing in a given amount of time , or how many times the injector is opened and closed in a given amount of time

50% duty cycle shows 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) and not a good thing

I dont feel it is safe to past 92% MAX

Tom
 

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Shot me 3 deer!!!
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Discussion Starter #5
so is this the same thing as injector pulse?
 

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Injector pulse is usually the actual amount of time that the injector is open, duty cycle is the percentage of is capacity that its operating at.
 

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The term "duty cycle" can be used for other devices that cycle on/off . It is not a term only for injector operation.

I think the idle speed motor on the Focus, also has a computer controlled duty cycle......at least some of these controllers operate this way.
 

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Dumbledore dies?!?!
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I love this new tuning section. Full of great questions, and very to the point answers.
 

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Dutycycle isnt a number you pick its more how much work there doing the more work (boost / incoming air ) the more the duty cycle on the injectors goes up to maintain the target AF

Tom
 

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If 85% is where you feel safe then stop there ,Injectors have come a long way in the last few years but allways do what you feel is the safest

Tom
 

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C2H5OH
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Now I'm curious on this one. Tom made lite of "time" being part of the equation.
What is "time" in this sense?
Is it 1 rotation of the crank, i.e. rpm; or is it based on milliseconds or some other fractional second.


I only ask because on the ecotec forums a guy made lite of the GM super/turbo cars will report up to 120% duty cycle, he showed me the logs to prove this. I'm still confused on the whole thing.
 

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Time with dutycycle is how fast the injector can open and close in a given amount of time
Yes you can go past 100% but you take HUGE chance of hurting the injector or sticking it open , they shouldnt be taken that far

Tom
 

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if duty cycle is pretty much a ratio of time on vs time off, how is it possible to have a duty cycle of 120%?
 

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Impossible

if duty cycle is pretty much a ratio of time on vs time off, how is it possible to have a duty cycle of 120%?
In what context?

It's absolutely impossible to achieve 120% duty cycle, you get to 100% and the injector (or other component like a purge valve, EGR etc) is being energized constantly.

There simply is no 120% Duty Cycle. (Think of the silly things we used to say when we were 7, like "double infinity"[neener] )

But you could arrive at a theoretical value of 120% Duty Cycle as the result of an ECU calcualtion for fuel delivery requirements and injector flow rates plugged into the calibration.
 

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In what context?

It's absolutely impossible to achieve 120% duty cycle, you get to 100% and the injector (or other component like a purge valve, EGR etc) is being energized constantly.

There simply is no 120% Duty Cycle. (Think of the silly things we used to say when we were 7, like "double infinity"[neener] )

But you could arrive at a theoretical value of 120% Duty Cycle as the result of an ECU calcualtion for fuel delivery requirements and injector flow rates plugged into the calibration.
I use to feel the same way , that 100% is it all it can do till I saw my fluke meter with the proble in the injector hit 103% on more then one car , granted it could be a calculation error or a fluke with the fluke but have seen it

Tom
 
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