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Old 11-26-2007, 06:46 PM   #1
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Default Fuel Pressure Change/Tuning Issue

Okay...so I messed up and didn't verify my fuel pressure at idle before I did my tuning. I have a majority of my tuning exactly the way I want it. Fuel Pressure at idle is at 50psi and I am wanting to change it to 35psi. Is there a calculation I can use to modify the existing table to compensate for the lower pressure?

Idle w/ 1000cc/min injectors at 50psi is running a 11:1 AFR on minimum injector timing.

I am hoping that lowering to 35psi it will get closer to reasonable. Any input is greatly appreciated.
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Old 11-26-2007, 07:39 PM   #2
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sqrt(new pressure/old pressure) x old flow rate = new flow rate

You're running a TecGT right? Does it support sequential ignition? Do you enter your fuel map in injector pulsewidth or in VE?

current VE entry x (observed afr/desired afr) = desired VE entry

all that being said, it may not be possible to have a great idle w/ 1k cc/min injectors with such a small motor.
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Old 11-26-2007, 08:17 PM   #3
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Agreed, I may not get a great Idle. But before the new motor I could idle at about 13:1 and that was with the 1.8. I am hoping that I can at least get that close.

Those formulas are going to be tattooed on the back of my hand...I am going to be using them constantly.
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Old 11-26-2007, 08:32 PM   #4
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Forgot to answer questions.....

I am running the TecGT. It doesn't support sequential ignition. In the Fuel Map I enter in VE. I can view the fuel table in pulsewidth, but I can't figure out how to modify it while in that view...only in VE Display. Of course, I can play around with it some more to see if I can.

Thanks
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Old 11-26-2007, 10:29 PM   #5
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So it just shows PW damn that kind of sucks. I think the move down to 35 psi should help you alot. Are your injectors low impedance by any chance to support low duty cycles like that it would be better.
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Old 11-26-2007, 10:35 PM   #6
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Quote:
Originally Posted by mikef85 View Post
Forgot to answer questions.....

I am running the TecGT. It doesn't support sequential ignition. In the Fuel Map I enter in VE. I can view the fuel table in pulsewidth, but I can't figure out how to modify it while in that view...only in VE Display. Of course, I can play around with it some more to see if I can.

Thanks
No, that's great. Working with VE is easier than working with PW because you can much more easily and quickly dial in your fuel map. If I needed as much fuel as you, I would want to either run sequential or maybe even staged injection, but I'd put the "primary" injectors in the IM and the big 1k injectors in the stock fuel rail position.
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Old 11-27-2007, 12:48 AM   #7
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Quote:
Originally Posted by magnamx-5 View Post
So it just shows PW damn that kind of sucks. I think the move down to 35 psi should help you alot. Are your injectors low impedance by any chance to support low duty cycles like that it would be better.
The injectors are low impedence

Moving the pressure down to 35psi tomorrow morning, we'll see how bad things get screwed up...
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Old 11-27-2007, 12:52 AM   #8
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No, that's great. Working with VE is easier than working with PW because you can much more easily and quickly dial in your fuel map. If I needed as much fuel as you, I would want to either run sequential or maybe even staged injection, but I'd put the "primary" injectors in the IM and the big 1k injectors in the stock fuel rail position.
Just to clarify...the injectors are run in full sequential. They only spray once every two revolutions. So, that helps a lot with things. You mentioned sequential ignition and I was kind of curious why ignition would play a role in it, haha.

We'll see how it goes, I modified a copy of my file, hopefully I got it remotely close. I adjusted it to add about .5 ms throughout the map. Thanks
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Old 11-27-2007, 09:48 AM   #9
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meant injection
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