measured injector duty cycle : a question now.
02-26-2002, 11:11 PM
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measured injector duty cycle : a question now.
car is a supercharged 2000 prelude sh at 6psi with various bandaids. 370cc injectors, rr fmu, etc.
should duty cycle vary proportionally with RPM? i assume that, other things being equal (load, etc) the injector would open the same amount of time at 7400rpm as it would at 3700rpm, which would yield 1/2 the duty cycle at 3700rpm due to the entire power cycle being twice as long. is this correct? or is it possible to hold the injectors open LONGER at mid or low RPMs than 1/(redline/60) seconds? on this motor, 100% duty cycle at fuel cutoff would be 8ms. so does that mean the maximum time the injector is EVER open below 7600rpm is 8ms at a time?
my duty cycle measured about 85% just before the fuel cutoff. it seemed to scale fairly proportionally to that lower and lower in the power band. at idle it was 1.7 -> 2.0%.
i am curious about this because it was very very hard (and took pretty high fuel pressure) to get the car running safely (i.e. not too lean) in the midrange. we then leaned it out a bit up top with a VAFC. but since the duty cycle read like 50% at 4000RPM, shouldn't it be possible to richen it A LOT (if you had, say, a standalone) without increasing the fuel pressure?
sorry if this is a stupid question; i did some searches and looked around on diy_efi but couldn't really find anything.
should duty cycle vary proportionally with RPM? i assume that, other things being equal (load, etc) the injector would open the same amount of time at 7400rpm as it would at 3700rpm, which would yield 1/2 the duty cycle at 3700rpm due to the entire power cycle being twice as long. is this correct? or is it possible to hold the injectors open LONGER at mid or low RPMs than 1/(redline/60) seconds? on this motor, 100% duty cycle at fuel cutoff would be 8ms. so does that mean the maximum time the injector is EVER open below 7600rpm is 8ms at a time?
my duty cycle measured about 85% just before the fuel cutoff. it seemed to scale fairly proportionally to that lower and lower in the power band. at idle it was 1.7 -> 2.0%.
i am curious about this because it was very very hard (and took pretty high fuel pressure) to get the car running safely (i.e. not too lean) in the midrange. we then leaned it out a bit up top with a VAFC. but since the duty cycle read like 50% at 4000RPM, shouldn't it be possible to richen it A LOT (if you had, say, a standalone) without increasing the fuel pressure?
sorry if this is a stupid question; i did some searches and looked around on diy_efi but couldn't really find anything.
02-27-2002, 06:35 AM
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Re: measured injector duty cycle : a question now. (schwett)
I know RC Engineering has a website they specialize in fuel injection. I'm sure they could help you.
With standalone systems you can play with the injector pulse thus make it richer without increasing fuel press.
With standalone systems you can play with the injector pulse thus make it richer without increasing fuel press.
02-27-2002, 08:34 AM
#3
Re: measured injector duty cycle : a question now. (schwett)
Injector duty cycle is relative to throttle position and rpm. Full throttle at higher rpm's the injector duty cycle climbs to 85%, which is the peak operating efficiency for stock injectors.
To answer your question about being able to run the car richer, you will need to get a standalone to do that. Basically running larger injectors and standalone goes hand in hand. The purpose of a larger injector is to be able to run the injector at lower duty cycles, while the injector spits out more fuel. Standalones directly control the duty cycle of the injector, or better known as injector pulse width. The V-AFC that you have just alters the MAP sensor signals, which allows you to enrich or lean out the injectors by altering the voltage readings. There isnt much room to control the injectors, and the V-AFC will not contol larger injectors, since it the stock ecu cannot control them, which the V-AFC gets its reading from. From being on this site you probably see the pattern developing that you need to get a standalone and larger injectors to fully tune your car. You are just joking yourself with all the bandaids. For the price of the bandaids you could now have a AEM EMS, or even a Hondata.
To answer your question about being able to run the car richer, you will need to get a standalone to do that. Basically running larger injectors and standalone goes hand in hand. The purpose of a larger injector is to be able to run the injector at lower duty cycles, while the injector spits out more fuel. Standalones directly control the duty cycle of the injector, or better known as injector pulse width. The V-AFC that you have just alters the MAP sensor signals, which allows you to enrich or lean out the injectors by altering the voltage readings. There isnt much room to control the injectors, and the V-AFC will not contol larger injectors, since it the stock ecu cannot control them, which the V-AFC gets its reading from. From being on this site you probably see the pattern developing that you need to get a standalone and larger injectors to fully tune your car. You are just joking yourself with all the bandaids. For the price of the bandaids you could now have a AEM EMS, or even a Hondata.
02-27-2002, 09:30 AM
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Re: measured injector duty cycle : a question now. (boosted hybrid)
right. i know all this... the cost of a standalone is actually a lot more than a vafc and fmu, but that's beside the point. i can't go standalone without losing my atts system, which i'm not going to do.
but it sounds like the answer to my original question is that the stock ECU does NOT ever command the injectors to a larger pulse width than what you can get at fuel cutoff. there's only 8ms of possible time for the injector to be open at 7600rpm, and while there's 16ms at 3800rpm the ecu is still directing an 8ms pulse. is this right?
but it sounds like the answer to my original question is that the stock ECU does NOT ever command the injectors to a larger pulse width than what you can get at fuel cutoff. there's only 8ms of possible time for the injector to be open at 7600rpm, and while there's 16ms at 3800rpm the ecu is still directing an 8ms pulse. is this right?
Injector duty cycle is relative to throttle position and rpm. Full throttle at higher rpm's the injector duty cycle climbs to 85%, which is the peak operating efficiency for stock injectors.
To answer your question about being able to run the car richer, you will need to get a standalone to do that. Basically running larger injectors and standalone goes hand in hand. The purpose of a larger injector is to be able to run the injector at lower duty cycles, while the injector spits out more fuel. Standalones directly control the duty cycle of the injector, or better known as injector pulse width. The V-AFC that you have just alters the MAP sensor signals, which allows you to enrich or lean out the injectors by altering the voltage readings. There isnt much room to control the injectors, and the V-AFC will not contol larger injectors, since it the stock ecu cannot control them, which the V-AFC gets its reading from. From being on this site you probably see the pattern developing that you need to get a standalone and larger injectors to fully tune your car. You are just joking yourself with all the bandaids. For the price of the bandaids you could now have a AEM EMS, or even a Hondata.
To answer your question about being able to run the car richer, you will need to get a standalone to do that. Basically running larger injectors and standalone goes hand in hand. The purpose of a larger injector is to be able to run the injector at lower duty cycles, while the injector spits out more fuel. Standalones directly control the duty cycle of the injector, or better known as injector pulse width. The V-AFC that you have just alters the MAP sensor signals, which allows you to enrich or lean out the injectors by altering the voltage readings. There isnt much room to control the injectors, and the V-AFC will not contol larger injectors, since it the stock ecu cannot control them, which the V-AFC gets its reading from. From being on this site you probably see the pattern developing that you need to get a standalone and larger injectors to fully tune your car. You are just joking yourself with all the bandaids. For the price of the bandaids you could now have a AEM EMS, or even a Hondata.
02-27-2002, 02:31 PM
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Re: measured injector duty cycle : a question now.
hmm, how are you measuring injector duty cycle?
I don't see why you couldn't run it lnoger than 8ms or whatever...
take this for example:
suppose redline/fuel cut is at 8000rpm.
suppose max torque/hp is at 7000rpm.
Presumably if you have more power at 7000rpm than 8000rpm, then that also means that you have more air & fuel going through the engine, which means that your injectors will be open for longer at 7000rpm than they are open at 8000rpm... does make sense?
-Xerxes
I don't see why you couldn't run it lnoger than 8ms or whatever...
take this for example:
suppose redline/fuel cut is at 8000rpm.
suppose max torque/hp is at 7000rpm.
Presumably if you have more power at 7000rpm than 8000rpm, then that also means that you have more air & fuel going through the engine, which means that your injectors will be open for longer at 7000rpm than they are open at 8000rpm... does make sense?
-Xerxes
02-27-2002, 02:46 PM
#7
Re: measured injector duty cycle : a question now. (schwett)
I was also actually wondering how you were measuring the pulse width. I know that on my PMS system i read the ms to never be over 8ms.
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02-27-2002, 02:55 PM
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Re: measured injector duty cycle : a question now. (boosted hybrid)
I was also actually wondering how you were measuring the pulse width. I know that on my PMS system i read the ms to never be over 8ms.
[Modified by LsTurbo91, 3:57 PM 2/27/2002]
02-27-2002, 03:27 PM
#9
Re: measured injector duty cycle : a question now. (schwett)
My mistake...i usually never look at the ms readings. I only ever pay attention to the duty cycle readings that it gives me. I just remember glancing at screen when data logging and remember seeing the pulse width never climbing over 8ms, but i just remember that i was keeping the throttle constant. 
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