No Device: scatter graphs and statistics
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Road Warrior
Joined: Mar 2013
Posts: 1,923
Likes: 587
From: Alorton, Illinois
8% to 10% is normally about one AFR so 12% is close to 1.5 AFR or the 14 AFR we had at 8.86 pulse width will end up about 15.5 AFR
If you take 14 AFR * 1.126 = 15.8 as the new AFR in theory. That is real close to our 15.5 AFR Rule of Thumb guess.
So a swing of Pulse Width of 8.86 to 7.98 will swing the AFR right at 1.5 AFRs if there is no other changes in RPM or throttle position or MAP.
Everyone follow me so far?
Andy
I'm going to take dead time out of the equation for simple math. Besides, dead time is going to be different depending on how the injector is built and if it is a low or high impedance injector and I think it will just confuse people. Let's just state that injectors have dead time.
A 4.3gps injector is going to deliver 4.3 grams a second. This is .0043 grams a ms. 1000 ms in a second. So changing the opening time of the injector a ms is going to add .0043 grams of fuel.
A 5.3gps injector is spraying .0053 grams/ms. Adding a ms to opening time is going to add .0053.
6.2 is .0062
8.7 is .0087
So, that kills your rule of thumb. I understand what you would like to do but you are really going the long way to get there. We have to know IPW to know IDC. Why not just deal with IPW and use IDC as it is meant to be used. To tell if you have control over the injector?
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Road Warrior
Joined: Mar 2013
Posts: 1,923
Likes: 587
From: Alorton, Illinois
We can also look at pressure or more important differential pressure. A injector that is rated at X is at a certain pressure spraying into atmosphere. Take perfect constant fuel pressure of 55psi.
An injector is actually going to spay more than that X amount if spraying into a vacuum. Say 40 kpa. Which converts to about 5.8 psi but remember that is a vacuum because atmosphere is 14.7. Then go the other way of force induction of 10 psi and to make this worse. With something like a procharger. Boost climbs with RPM.
This is one of the reasons I like a VE based system and so glad I don't have to deal with straight IPW as much.
An injector is actually going to spay more than that X amount if spraying into a vacuum. Say 40 kpa. Which converts to about 5.8 psi but remember that is a vacuum because atmosphere is 14.7. Then go the other way of force induction of 10 psi and to make this worse. With something like a procharger. Boost climbs with RPM.
This is one of the reasons I like a VE based system and so glad I don't have to deal with straight IPW as much.
Road Warrior
Joined: Jun 2015
Posts: 1,325
Likes: 140
From: Edinburgh UK
Guys, of course I know it is ...but is injector lag time really relevant?
Within the closed-loop management lambda from the O2 sensor is read and fueling adjusted to get the right number. That negates tolerance differences between injectors and, presumably, lag.
The other obvious point surely is that if there is a lag for the valve to actually open, then there is a lag for it it shut as well, no? cancelling each other out??
This isn't direct injection, it just chucks fuel onto the back of the valve even when it's shut?
Within the closed-loop management lambda from the O2 sensor is read and fueling adjusted to get the right number. That negates tolerance differences between injectors and, presumably, lag.
The other obvious point surely is that if there is a lag for the valve to actually open, then there is a lag for it it shut as well, no? cancelling each other out??
This isn't direct injection, it just chucks fuel onto the back of the valve even when it's shut?
Road Master
Joined: Mar 2007
Posts: 1,177
Likes: 23
The delay to open and the delay to close are different by about 1 ms. This 1 ms varies quite a bit based on the voltage supplied to the injector. This is why the ecu has to track the bike system voltage. There is a Harley hidden table that controls this and if it is perfect AND you are using their injectors, things should be close. If you get into larger injectors that do not have this table set right, low speed fuel control gets to be a problem.
(Opening time - closing) time also known as dead time can be a huge issue if you choose to ignore it. It shows up as a wide line at the lower left corner of the MAPXRPM vs DC plot when you have the issue.
Andy
(Opening time - closing) time also known as dead time can be a huge issue if you choose to ignore it. It shows up as a wide line at the lower left corner of the MAPXRPM vs DC plot when you have the issue.
Andy
Road Master
Joined: Mar 2007
Posts: 1,177
Likes: 23
The pressure differential thing the Jason was talking about gets to be an issue on the turbocharger type installs. The typical work around is installing a pressure referenced fuel pressure regulator. This is very common in the rice world. Google RRFPR and turbo.
The rule of thumb is you need a minimum of 42 PSI difference between the fuel rail absolute pressure and the absolute air pressure in the intake.
Andy
The rule of thumb is you need a minimum of 42 PSI difference between the fuel rail absolute pressure and the absolute air pressure in the intake.
Andy
Last edited by whittlebeast; Jul 1, 2016 at 06:10 AM.
Thread Starter
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Road Warrior
Joined: Mar 2013
Posts: 1,923
Likes: 587
From: Alorton, Illinois
Guys, of course I know it is ...but is injector lag time really relevant?
Within the closed-loop management lambda from the O2 sensor is read and fueling adjusted to get the right number. That negates tolerance differences between injectors and, presumably, lag.
The other obvious point surely is that if there is a lag for the valve to actually open, then there is a lag for it it shut as well, no? cancelling each other out??
This isn't direct injection, it just chucks fuel onto the back of the valve even when it's shut?
Within the closed-loop management lambda from the O2 sensor is read and fueling adjusted to get the right number. That negates tolerance differences between injectors and, presumably, lag.
The other obvious point surely is that if there is a lag for the valve to actually open, then there is a lag for it it shut as well, no? cancelling each other out??
This isn't direct injection, it just chucks fuel onto the back of the valve even when it's shut?
It's not really relevant for us on a VE based system. It is good to be aware of and it sounds real tech.
HD has two sides to the IPW equation. There is the air side, and the fuel side. We have control over the air side of the input. Dead time is dealt with on the fuel side.
BUT I believe it can come into play when choosing new injectors.
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Road Master
Joined: Mar 2007
Posts: 1,177
Likes: 23
Here is what this all looks like in scatter plots. At any given RPM, you can see the range of Injector operation graphed in Pulse Width on the first on and Injector Duty Cycle on the second link.
http://www.nbs-stl.com/HarleyTuning/...%20in%20TT.png
http://www.nbs-stl.com/HarleyTuning/...%20in%20TT.png
This is data of my Sporty running Target Tune. As a rule of thumb, you should avoid a minimum Pulse Width of less than 2ms and avoid a Duty Cycle of over 85%
Having fun learning EFI every day.
Andy
http://www.nbs-stl.com/HarleyTuning/...%20in%20TT.png
http://www.nbs-stl.com/HarleyTuning/...%20in%20TT.png
This is data of my Sporty running Target Tune. As a rule of thumb, you should avoid a minimum Pulse Width of less than 2ms and avoid a Duty Cycle of over 85%
Having fun learning EFI every day.
Andy
Last edited by whittlebeast; Jul 1, 2016 at 08:57 AM.
Road Master
Joined: Mar 2007
Posts: 1,177
Likes: 23
Here is what a BIG Twin with fuel cut enabled looks like. Notice how the Pulse Width does not get much below 2ms. Also the Duty cycle never gets over 75% DC.
http://www.nbs-stl.com/HarleyTuning/...Big%20Twin.png
Andy
http://www.nbs-stl.com/HarleyTuning/...Big%20Twin.png
Andy