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Old 02-07-2013, 01:34 AM   #1
StIGC11
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E85

Default Fuel Pressure

Currently have a AEM FPR with custom -6AN lines running to the 5/16 hardlines on the firewall, with Boomba racing fuel rails and dw 1300cc injectors.

From what I read the static fuel pressure should be 43.5psi and the base fuel pressure should be around 38psi.

Now when I adjusted my static fuel pressure to 43.5psi my base pressure dropped to 33.5psi, So in order to compinsate I adjusted the static fuel pressure to 48psi which made the base fuel pressure 38psi.

My elevation is 2,400'
Vac that is being pulled is -22

Is this normal?
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Old 02-07-2013, 12:34 PM   #2
kellygnsd
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You need to get you terms right because I'm not sure what you'r talking about. I don't know what you mean by static fuel pressure.

To set base fuel pressure you disconnect the vacuum line and set the FPR to 43.5 psi or whatever you want you base fuel pressure to be. With your vacuum line hooked up your fuel pressure will indicate base - vacuum. If you set you base to 43.5 that's the only adjustment needed.
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Old 02-07-2013, 12:38 PM   #3
Flat 4 Motorsport
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To add to Kellys post :

Fuel pressure will also rise with boost.

if your base pressure is 43.5, thats what it is until the manifold (vacuum source your fpr is routed to for reference) see's positive pressure and rises on a 1:1 ratio.
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Old 02-07-2013, 12:43 PM   #4
StIGC11
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Static fuel pressure = no vac line connected to fpr

Base fuel pressure = vac line connected.
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Old 02-07-2013, 12:47 PM   #5
StIGC11
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I know how the system works with boost and everything else I just have yet to see fuel pressure drop by 10psi when a vac line is connected.

Like I said most cars with no vac line connected will read 43.5psi then when the vac line gets connected to the fpr it drops to 38 psi that's 5.5psi diff. Mine drops 10psi. Why?
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Old 02-07-2013, 01:14 PM   #6
kellygnsd
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Quote:
Originally Posted by StIGC11 View Post
Static fuel pressure = no vac line connected to fpr

Base fuel pressure = vac line connected.
That's not what the FSM call it. Base fuel pressure is set how i mentioned before. When you hook up your vacuum line it will change accordingly based on vacuum or boost. You ate aware how a rising rate fpr works right?
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Old 02-07-2013, 01:15 PM   #7
kellygnsd
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Quote:
Originally Posted by StIGC11 View Post
I know how the system works with boost and everything else I just have yet to see fuel pressure drop by 10psi when a vac line is connected.

Like I said most cars with no vac line connected will read 43.5psi then when the vac line gets connected to the fpr it drops to 38 psi that's 5.5psi diff. Mine drops 10psi. Why?
It depends on how much vacuum you make at idle
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Old 02-07-2013, 01:33 PM   #8
StIGC11
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Ok that's all I needed to know Is that it can vary on how much vac is being pulled.
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Old 02-07-2013, 02:14 PM   #9
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Quote:
Originally Posted by StIGC11 View Post
Ok that's all I needed to know Is that it can vary on how much vac is being pulled.
Measured fuel pressure on a 1:1 regulator will ALWAYS be your base pressure (the real base pressure, not what you're calling the "base pressure" in this thread) plus manifold pressure (or minus manifold vacuum, as the case may be). If you're pulling 10 psi of vacuum at idle, your measured fuel pressure will be 10 psi below your base. That is unless your fuel pump is overrunning the FPR, in which case it will be a little higher, or if you're sucking the fuel pump dry, in which case it will be a little lower.
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