Question about fuel injection from a newbie

pbp1 · 05-06-2017, 10:51 AM

Now that you are logging Fuel Pressure, and you see that the pressure is dropping drastically, you have narrowed the root cause of the issue down to the fuel delivery system.
I personally think that 30# injectors running at their standard set pressure are borderline, but lets get your fuel delivery problem fixed first, and then, re-evaluate the injectors. Once you get the fuel delivery problem fixed, you will need to lower the pulsewidth numbers in your fuel table because right now, they are inflated from trying to compensate for the lack of fuel flow. Once the fuel pressure is constant, you will need to lower the pw numbers, which will bring your duty cycle down.
Think of it like this, at 25 psi, you injectors no longer flow 30# per hour. At 25 psi, they are more like 20#s per hour, so that's what you have at WOT.
Here's some simple math that applies:

The Fuel Consumption for this type of engine should be around .42 - .45#s per hr. If your engine makes 500hp, then it will need between 210 - 225#s per hr.

225 divided by 8 injectors = 28.125#s needed per injector.

If your injectors can flow a maximum of 30#s, and you need 28.125#s from them, then 28.125# divided by 30 = .9375 or 93.75% duty cycle.

If you raise the fuel pressure (and the fuel system is able to maintain that pressure at WOT), that raises the potential flow of the injector.
If your injectors are rated to flow 30#s at 45 psi, then they will flow around 35#s at 60 psi.

Now, you have 35# injectors, so the fuel you need - 28.125# divided by 35# = .80 or 80% duty cycle.

If I were you, I would fix the fuel delivery issue first. Then, I would upgrade to 36# injectors just to give you a little more margin for error.

05-06-2017, 10:51 AM	#11
pbp1 Junior Member Join Date: Mar 2013 Posts: 80 Likes: 12 Liked 27 Times in 6 Posts	Re: Question about fuel injection from a newbie Now that you are logging Fuel Pressure, and you see that the pressure is dropping drastically, you have narrowed the root cause of the issue down to the fuel delivery system. I personally think that 30# injectors running at their standard set pressure are borderline, but lets get your fuel delivery problem fixed first, and then, re-evaluate the injectors. Once you get the fuel delivery problem fixed, you will need to lower the pulsewidth numbers in your fuel table because right now, they are inflated from trying to compensate for the lack of fuel flow. Once the fuel pressure is constant, you will need to lower the pw numbers, which will bring your duty cycle down. Think of it like this, at 25 psi, you injectors no longer flow 30# per hour. At 25 psi, they are more like 20#s per hour, so that's what you have at WOT. Here's some simple math that applies: The Fuel Consumption for this type of engine should be around .42 - .45#s per hr. If your engine makes 500hp, then it will need between 210 - 225#s per hr. 225 divided by 8 injectors = 28.125#s needed per injector. If your injectors can flow a maximum of 30#s, and you need 28.125#s from them, then 28.125# divided by 30 = .9375 or 93.75% duty cycle. If you raise the fuel pressure (and the fuel system is able to maintain that pressure at WOT), that raises the potential flow of the injector. If your injectors are rated to flow 30#s at 45 psi, then they will flow around 35#s at 60 psi. Now, you have 35# injectors, so the fuel you need - 28.125# divided by 35# = .80 or 80% duty cycle. If I were you, I would fix the fuel delivery issue first. Then, I would upgrade to 36# injectors just to give you a little more margin for error.