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How to correct High fuel pressure on a new build STI?
How to correct High fuel pressure on a new build STI?
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Old 03-29-19, 10:56 AM   #1
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Default How to correct High fuel pressure on a new build STI?

Hoping i can get some help/advise/insight from you guys.

Decided to rebuild the engine after a rod knock in my 15STI, now I m having an issue with high fuel pressure (58 PSI), idle gets bouncy after it is warm up. It is impossible to drive it without stalling all the time. The ECU has been flashed with a new basemap from a local tuner, assuming it was done correctly based on my mods.

At idle, the FP reads 58psi. The fuel sensor was installed on the FPR on the return line before the ethanol sensor. But when the supply line gets pinched the pressure can drop down to 42psi, idle will stable, and the WB 450 pump inside the surge tanks whines.

The radium surge tank has 4x -6 line connections, WB450 hardwired to the battery. Also a hard wire kit tapping the relay to the fuel pressure controller in the trunk.

BOV is tight shut at idle, no sign of vacuum leak.


Build:

Dom XT 1.5
1700 CC injectors
TGV deletes
Killerbee ELH
Killerbee oil pan and pickup
3 inch inlet
New built motor with forged internals
Cobb AOS

Cobb Flex fuel kit with fuel pressure sensor
Aeromotive Fuel Pressure regulator

Radium surge tank with WB 450
Aeromotive 325 in stock tank
Stock fuel rails

Any help will be appreciated.

Thanks.
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Old 03-29-19, 11:41 AM   #2
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Default Re: How to correct High fuel pressure on a new build STI?

Adjust the fuel pressure regulator. If that doesn't work, warranty it.
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Old 03-29-19, 03:23 PM   #3
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Default Re: How to correct High fuel pressure on a new build STI?

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Originally Posted by yamahaSHO View Post
Adjust the fuel pressure regulator. If that doesn't work, warranty it.
This.

Your aftermarket FPR needs to be adjusted to the pressure your tuner wants.
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Old 03-30-19, 08:42 AM   #4
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Default Re: How to correct High fuel pressure on a new build STI?

Quote:
Originally Posted by yamahaSHO View Post
Adjust the fuel pressure regulator. If that doesn't work, warranty it.
the adjustable FPR is already maxed out.

It might be back pressure created in the return line in the oem fuel pump hangar. I was told that the venturi becomes a restriction in the oem tank, and should get a Radium fuel pump hangar.
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Old 03-30-19, 08:44 AM   #5
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Default Re: How to correct High fuel pressure on a new build STI?

Quote:
Originally Posted by Noximus View Post
This.

Your aftermarket FPR needs to be adjusted to the pressure your tuner wants.
My tuner said that it is mechanical when the base pressure is out of spec, should be corrected first. He doesn't tune around mechanical issues.
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Old 03-30-19, 08:47 AM   #6
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Default How to correct High fuel pressure on a new build STI?

Quote:
Originally Posted by MY15STI View Post
the adjustable FPR is already maxed out.



It might be back pressure created in the return line in the oem fuel pump hangar. I was told that the venturi becomes a restriction in the oem tank, and should get a Radium fuel pump hangar.


What kind of fuel pressure are you looking for? It shouldn’t be maxed out if you need to lower it?!

I have the same FPR as you, and I was able to set my idle fuel pressure perfectly with plenty of adjustment still available. You don’t want your idle fuel pressure to be 60psi, that would put your WOT fp around 80-90psi...(depending on your boost level)

Last edited by Noximus; 03-30-19 at 08:51 AM.
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Old 03-30-19, 08:51 AM   #7
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Default How to correct High fuel pressure on a new build STI?

Quote:
Originally Posted by MY15STI View Post
My tuner said that it is mechanical when the base pressure is out of spec, should be corrected first. He doesn't tune around mechanical issues.


If you remove the vacuum line on your FPR, you want your FP to be at 43.5.

Under full boost, this puts me around 64.5psi since I’m tuned for 21psi.
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Old 03-30-19, 08:56 AM   #8
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Default Re: How to correct High fuel pressure on a new build STI?

I have a bigger jet pump, but prior to installing that, I ran the stock one without issue. That said, I have a 2005 and the hangar is different.

Are you saying you cannot go any lower on pressure when you back it off with the regulator? I wouldn't expect any decent tuner to tune around this. We are going off whatever little information you provided. If you disconnect the feed pump in the tank, does it allow you to bring the pressure down with just the surge tank using what's in the tank (and its return back into the surge tank)?

Be sure you are setting base pressure without vacuum or boost.
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Old 03-30-19, 10:53 AM   #9
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Default Re: How to correct High fuel pressure on a new build STI?

Quote:
Originally Posted by Noximus View Post
What kind of fuel pressure are you looking for? It shouldn’t be maxed out if you need to lower it?!

I have the same FPR as you, and I was able to set my idle fuel pressure perfectly with plenty of adjustment still available. You don’t want your idle fuel pressure to be 60psi, that would put your WOT fp around 80-90psi...(depending on your boost level)
The idle pressure needs to be at around 42ish psi, but it is at 58+ psi. The Aeromotive FPR can't lower it anymore.

The static pressure with just the wb 450 pump in the surge tank running at 100% is at 42 psi.

Suspecting that it is back pressure coming from the OEM fuel pump hangar. Radium told me that it is because of the increasing fuel-flow, the venturi becomes a restriction, rendering the regulator useless.

"One solution is to use our fuel pump hanger for your vehicle. This gives multiple pump options, as well as incorporating our high flow venturi. This will operate at high fuel flow rates and still retain OEM functionality of the fuel tank."
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Old 03-30-19, 02:30 PM   #10
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Default Re: How to correct High fuel pressure on a new build STI?

If you turn off the pump in the tank, the surge tank will eliminate the factory hanger situation. If you cannot lower the base pressure when you disconnect power to the in-tank pump, your regulator is bad.
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