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Old 07-12-2020, 05:28 PM   #1
wrxchitown
Scooby Newbie
 
Member#: 185520
Join Date: Jul 2008
Chapter/Region: SCIC
Location: San Diego, CA
Vehicle:
2015 Sti launch
Blue

Default Need help with a fuel pressure issue

I’m trying to figure out what is causing my fuel pressure to drop. I have an aeromotive a1000 FPR, AEM 340 fuel pump, ID1300s, A/N -6 fuel lines, and using a Cobb fuel pressure sensor logging through access port. My fuel system schematic is the following. AEM pump In tank, from the black fuel line at fire wall to Y splitter, front of fuel rails, out back of rails to aeromotive a1000 FPR(sides), out the bottom of the FPR to Cobb flex fuel sensor, out flex fuel sensor to gray fuel line at firewall. Cobb fuel sensor is connected to the sensor port on the FPR. The issue that I am having is that when I remove the vacuum line my pressure increases to roughly 50 PSI, vacuum line hooked up(-19 in mercury / -9.5PSI) the fuel pressure drops to 45psi. I tested vacuum at the line between manifold and FPR with an analog boost gauge. During normal driving the car shows between 45 and 50 PSI while in vacuum. When in boost at higher RPMs the pressure drops down to an adjusted 45 PSI base(final pressure minus boost). I did a test where I pinched off the return line, let the line get to 80 PSI, turned car off, released pinched line and the pressure dropped to 45 PSI it held there for well over 5 min. Does anybody have any ideas. I’m planning on throwing the stock fuel pump in to see how it responds. I just filled my tank so I need to burn some fuel off first.

So my questions are
1. Shouldn’t my base pressure be dropping from 50PSI to close to 40 under 9.5PSI vacuum?
2. Shouldn’t the adjusted base pressure under boost remain at the 50 PSI that I am seeing with the vacuum line disconnected? If so what could be causing the drop?
3. If the FPR is holding the pressure at 45 psi with the car off shouldn’t my base pressure with no vacuum be 45PSI?

I’m new to adjustable fuel pressure regulators and logging fuel pressure in general. So I’m not sure if this is normal behavior on our cars.

Car info:
2015 STI
BCP X500+ (18psi)
ACN 91
Grimmspeed TMIC
AEM 340
ID1300
TGV delete
Cobb SF intake with box
Perrin turbo inlet
Invidia downpipe and cat back
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Old 07-13-2020, 12:45 PM   #2
wrxchitown
Scooby Newbie
 
Member#: 185520
Join Date: Jul 2008
Chapter/Region: SCIC
Location: San Diego, CA
Vehicle:
2015 Sti launch
Blue

Default

I spoke with aeromotive this morning. They said it might be a restrictive fuel return. Are there any known restrictions or common failures to look for in our cars?
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