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Low fuel pressure?

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Old 06-26-2011, 09:59 PM   #1
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Default Low fuel pressure?

Hey guys, I just recently purchased a fuel pressure gauge, a 340 lph fuel pump,and an AEM fuel pressure regulator. Before these parts were purchased, I had a Walboro 255. I'm currently running Deastcwerks 1000 cc injectors. My first issue is that when I turn my car off, the fuel pressure instantly drops to zero with my AEM FPR. I switched it back to the stock FPR, and it holds at 29 psi after i turn the engine off. Is this normal for an AEM APR, and is 29 psi normal pressure for the stock FPR? The next problem is, my fuel pressure on the stock regulator is at 40 psi with vacuum line disconnected, with the Vacuum line connected, it's at 35 psi. Isn't this very low? I thought the stock fuel pressure was suppose to be at 50 psi unconnected, and 40 psi connected. My fuel pump is brand new, and i did not find any leaks around my injectors or lines. For the fuel pump install, I used the stock clamps to connect the fuel line to the fuel pump.
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Old 06-27-2011, 03:08 PM   #2
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I had 45psi base pressure on my OEM regulator and used the same on the AEM. My tuner wanted the vacuum line connected and that gave around 60psi at 14psi boost.

Don´t know about the drop after you turn it off, never tested it on this car but know that a few race pumps come without the one way valve that OEM pumps have and then it would be normal. Maybe we have that valve in the FPR instead?
Either way you don´t need it if you can run the pump on ignition a few sec before cranking, that will help you reach the right pressure before start.
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Old 06-27-2011, 04:21 PM   #3
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The aem fpr won't hold fuel pressure once the car is off. Due to the nature of the design it's essentially an adjustable bleed type system. Mine does the same. Nothing to be worried about. Your stock fuel pressure does seem low though
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Old 06-27-2011, 06:17 PM   #4
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Originally Posted by o'malley_808 View Post
The aem fpr won't hold fuel pressure once the car is off. Due to the nature of the design it's essentially an adjustable bleed type system. Mine does the same. Nothing to be worried about. Your stock fuel pressure does seem low though
Thanks. My fuel pressure actually dropped down to 32 psi today, which I blame on 113 degree weather. I could turn up my fuel pressure with the AEM, but I feel like that would just be a bandage hiding the real issue. I have a completely new fuel system, just don't get why it would be that low unless I have a leak somewhere.
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Old 06-27-2011, 06:17 PM   #5
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Quote:
Originally Posted by B5254T4 View Post
I had 45psi base pressure on my OEM regulator and used the same on the AEM. My tuner wanted the vacuum line connected and that gave around 60psi at 14psi boost.

Don´t know about the drop after you turn it off, never tested it on this car but know that a few race pumps come without the one way valve that OEM pumps have and then it would be normal. Maybe we have that valve in the FPR instead?
Either way you don´t need it if you can run the pump on ignition a few sec before cranking, that will help you reach the right pressure before start.
Was the 45 psi base pressure with the vacuum line connected?
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Old 06-27-2011, 09:24 PM   #6
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Vacuum line off for the 45psi.

Check the pump hose, the short one in the tank. If you have a leak there you´ll lose (loose?) pressure.
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Old 06-27-2011, 09:57 PM   #7
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The AEM comes with 3 relief fittings for the bottom of the regulator. With the 340 pump i would use the middle one provided. Your stock fuel pressure does seem low.
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Old 06-27-2011, 10:09 PM   #8
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Originally Posted by B5254T4 View Post
Vacuum line off for the 45psi.

Check the pump hose, the short one in the tank. If you have a leak there you´ll lose (loose?) pressure.
That's the only thing it could be. I'm gonna replace it this weekend and use the screw clamps provided instead. I will provide updates if this fixes the issue.
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Old 06-27-2011, 10:10 PM   #9
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Originally Posted by jefferyg32 View Post
The AEM comes with 3 relief fittings for the bottom of the regulator. With the 340 pump i would use the middle one provided. Your stock fuel pressure does seem low.
Thanks. I'm gonna put the AEM back in once I figure out where my pressure is going.
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Old 07-01-2011, 01:30 PM   #10
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I just replaced the in tank fuel line, and used different clamps. My fuel pressure is still at 35 psi at idle. Maybe my 1000 cc injectors are draining too much fuel too fast from my fuel rail? Whatever it is, i'm just going to put the AEM FPR back in, and turn the fuel pressure to 40 psi.
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