Stock Injector Response Time
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Joined: Sep 2001
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From: Pflugerville, TX
Vehicle: 2000 Elantra
Are you asking a question about the drive signal, or about the injector's duty cycle?
(either way, from me the answer is "no" but if anyone else knows the answer, a more clearly phrased question might help)
(either way, from me the answer is "no" but if anyone else knows the answer, a more clearly phrased question might help)
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Joined: Feb 2009
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From: Boston
Vehicle: 2006 Pontiac GTO
^ Yeah, that's it, thank you very much!
Stocker, the question was very clearly phrased for those that know the answer haha tongue.gif It's the time it takes the injector to open from the time the current starts flowing (during this time no fuel is flowing). If it's 1ms, then the ECU adds 1ms to the calculated duty cycle. It is relevant when you're scaling the duty cycle for larger injectors - for example the AEM FIC will subtract this value from the duty cycle, rescale the duty cycle, then add the value back, makes sense?
Stocker, the question was very clearly phrased for those that know the answer haha tongue.gif It's the time it takes the injector to open from the time the current starts flowing (during this time no fuel is flowing). If it's 1ms, then the ECU adds 1ms to the calculated duty cycle. It is relevant when you're scaling the duty cycle for larger injectors - for example the AEM FIC will subtract this value from the duty cycle, rescale the duty cycle, then add the value back, makes sense?
Super Moderator
Joined: Sep 2001
Posts: 10,795
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From: Pflugerville, TX
Vehicle: 2000 Elantra
I know what a response time is, genious! For example, when the lights go green, add 0.4 seconds to the time it takes my car to start moving, and that's YOUR response time! nana.gif
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Joined: Mar 2006
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Vehicle: 2005/Hyundai/Tiburon
I have an 05 Tib with a Beta II motor, Alpine MP45 SC setup and an FIC for tuning.
I have been using 1174.5 uS and it works good on my car. The LTFT has been stable at air temps ranging from 60 to 90 degrees.
If the FIC IRT is set as close as possible to the OEM injectors IRT the LTFT shouldn't change much when the ECU adjusts the injector pulsewidth to compecsate for different air temps.
From AEM on IRT:
For every fuel injector, it takes a certain amount of time between when the ECU applies power to the injector and when fuel actually begins to spray out of the injector nozzle. This is sometimes referred to as injector dead time, injector response time, or battery offset (because the amount of time will be different depending on battery voltage).
The FIC compensates for Injector Response Time as follows: let's say the Injector Response Time is set to 500 us (0.5ms). This is assuming that when the stock ECU holds the injector open for 2.0 ms, the first 0.5ms of that time is spent opening the injector (without any fuel flow) and the next 1.5ms is spent actually delivering fuel to the engine. If you want to add exactly 100% more fuel, you should hold the injector open for (2.0 - 0.5) = 1.5 ms longer than what the stock ECU was doing.
The time spent opening the injector doesn't change, so the total fuel pulse to deliver double the fuel should be 0.5 + (1.5 * 2) = 3.5ms.
Hopefully that helps explain that the FIC essentially just holds onto the Injector Response Time. It is subtracted before fuel calculations are performed, then it is added back in after fuel calculations are performed.
I have been using 1174.5 uS and it works good on my car. The LTFT has been stable at air temps ranging from 60 to 90 degrees.
If the FIC IRT is set as close as possible to the OEM injectors IRT the LTFT shouldn't change much when the ECU adjusts the injector pulsewidth to compecsate for different air temps.
From AEM on IRT:
For every fuel injector, it takes a certain amount of time between when the ECU applies power to the injector and when fuel actually begins to spray out of the injector nozzle. This is sometimes referred to as injector dead time, injector response time, or battery offset (because the amount of time will be different depending on battery voltage).
The FIC compensates for Injector Response Time as follows: let's say the Injector Response Time is set to 500 us (0.5ms). This is assuming that when the stock ECU holds the injector open for 2.0 ms, the first 0.5ms of that time is spent opening the injector (without any fuel flow) and the next 1.5ms is spent actually delivering fuel to the engine. If you want to add exactly 100% more fuel, you should hold the injector open for (2.0 - 0.5) = 1.5 ms longer than what the stock ECU was doing.
The time spent opening the injector doesn't change, so the total fuel pulse to deliver double the fuel should be 0.5 + (1.5 * 2) = 3.5ms.
Hopefully that helps explain that the FIC essentially just holds onto the Injector Response Time. It is subtracted before fuel calculations are performed, then it is added back in after fuel calculations are performed.
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Joined: Feb 2009
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From: Boston
Vehicle: 2006 Pontiac GTO
^Thanks! I'm using ~1200us too for now (I think i got it from you on aempower forum haha), seems to be working good.
Yeah that's how I thought it worked too (same thing i said in post #4 above)
However, I'm confused about one thing - the injector also has a closing time, I don't really know why that isn't factored in the calculation. It seems the difference between opening and closing time should be used instead (for example if opening and closing times are the same, the fuel flow just lags a bit so if you want to add/subtract fuel, you should just rescale the entire pulse cycle).
Yeah that's how I thought it worked too (same thing i said in post #4 above)
However, I'm confused about one thing - the injector also has a closing time, I don't really know why that isn't factored in the calculation. It seems the difference between opening and closing time should be used instead (for example if opening and closing times are the same, the fuel flow just lags a bit so if you want to add/subtract fuel, you should just rescale the entire pulse cycle).
