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Old 07-04-2021, 08:37 PM   #1
e_navarre
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Thumbs down Fuel pressure drop at WOT

I know others have had this issue and I cant seem to find a resolution anywhere.

My STI isnít raising fuel pressure under boost. I have base pressure set to 43.5psi and under boost my fuel pressure diff actual drops down into 20s. It would seem that the AFPR is bad, but Iíve replaced my regulator, fuel pump, injector o rings, done a smoke test, tested the hard wiring to the pump and nothing will make fuel pressure rise enough to keep my diff actual a consistent 43.5. The only other thing I could think to do would be pull every line out and inspect for holes but the bay doesnít smell like gas. This issue happened out of no where.

Mods list:
Walbro 450lph pump with hardwire kit
Injector dynamics 1300cc injectors
Aeromotive AFPR
Cobb flex fuel/fuel pressure sensor
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Old 07-04-2021, 09:52 PM   #2
Marvick08GT
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Did you change the filter? (It's part of the pump assembly.)
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Old 07-04-2021, 10:32 PM   #3
e_navarre
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Originally Posted by Marvick08GT View Post
Did you change the filter? (It's part of the pump assembly.)
yes I should have mentioned that. I removed the in tank OEM filter and have an external 10micron radium filter which is new
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Old 07-04-2021, 11:21 PM   #4
benflynn
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Is it the calibration correct for the sensor? Wires correct? Pressure been verified with a mech gauge?
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Old 07-05-2021, 12:15 AM   #5
e_navarre
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Originally Posted by benflynn View Post
Is it the calibration correct for the sensor? Wires correct? Pressure been verified with a mech gauge?
Itís wired to the tgv, Iíve swapped out to an AEM sensor and noticed it reads about 10psi lower. I hooked a mechanical gauge up to my regulator and itís at 43.5 at idle and rises to about 60psi under boost, youíd think this is normal and all is fine but the car is noticeably down on power and boost, alongside the FP diff dropping. Plus the sensor was working fine... then one day not. Iím thinking maybe the harness went bad or the ecu is freaking out
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Old 07-05-2021, 10:18 AM   #6
benflynn
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The Cobb uses the fuel pressure information in the tune I think. If so Iíd disable that or unhook it and see how it runs. Or swapp it to the other tgv if u think u hurt the input or harness. I suspect we are giving the Cobb bad info and itís skewing the fueling maybe pulling boost. I run a merped flex sd rom so not so up on the Cobb
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Old 07-05-2021, 10:34 AM   #7
e_navarre
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Originally Posted by benflynn View Post
The Cobb uses the fuel pressure information in the tune I think. If so Iíd disable that or unhook it and see how it runs. Or swapp it to the other tgv if u think u hurt the input or harness. I suspect we are giving the Cobb bad info and itís skewing the fueling maybe pulling boost. I run a merped flex sd rom so not so up on the Cobb
Iíll give that a shot. Thereís no one thing I can point to that caused this. It was driving fine, then one day it felt like it got fuel cut at 5-6psi of boost and then didnít want to work
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Old 07-05-2021, 12:50 PM   #8
e_navarre
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Originally Posted by e_navarre View Post
Iíll give that a shot. Thereís no one thing I can point to that caused this. It was driving fine, then one day it felt like it got fuel cut at 5-6psi of boost and then didnít want to work
No change :/
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Old 07-21-2021, 11:33 PM   #9
e_navarre
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Update:
Iíve since replaced the hardwire kit and fuel pressure sensor kit with no change whatsoever. Iím at a total loss of what could be causing this issue. My only thoughts could be bad injector(s), something ecu related or avcs. Any input would be greatly appreciated because Iíve replaced literally every part of the fueling system and nothing has changed.
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Old 07-25-2021, 07:44 PM   #10
awnetve
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Iím having the same issue. Do you have the strainer / sock before the fuel pump? Do you see any change if you have the tank full?
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Old 07-25-2021, 09:28 PM   #11
DansharSti04
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Are you monitoring boost vs fuel pressure and is the pressure rising 1:1 with boost and then falling off as you stay in it causing FPDA to fall?
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Old 07-25-2021, 10:49 PM   #12
e_navarre
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Quote:
Originally Posted by awnetve View Post
Iím having the same issue. Do you have the strainer / sock before the fuel pump? Do you see any change if you have the tank full?
New sock did nothing and neither did a full tank of gas
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Old 07-25-2021, 10:51 PM   #13
e_navarre
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Originally Posted by DansharSti04 View Post
Are you monitoring boost vs fuel pressure and is the pressure rising 1:1 with boost and then falling off as you stay in it causing FPDA to fall?
Monitoring boost and FPDA, which drops at any load other than cruising, more severe as boost increase
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Old Yesterday, 05:56 PM   #14
DansharSti04
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Quote:
Originally Posted by e_navarre View Post
Monitoring boost and FPDA, which drops at any load other than cruising, more severe as boost increase
So do you build boost and fuel pressure does not rise from your base 43psi?

Last edited by DansharSti04; Yesterday at 06:17 PM.
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Old Today, 05:52 AM   #15
e_navarre
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Originally Posted by DansharSti04 View Post
So do you build boost and fuel pressure does not rise from your base 43psi?
Yes and no. Fuel pressure stays a constant 43.5psi, so under any load other than idle, itíll drop into the 30s at low-med loads and 20s at high load. FPDA isnít rising with boost as it should
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Old Today, 07:20 PM   #16
DansharSti04
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Quote:
Originally Posted by e_navarre View Post
Yes and no. Fuel pressure stays a constant 43.5psi, so under any load other than idle, itíll drop into the 30s at low-med loads and 20s at high load. FPDA isnít rising with boost as it should
FPDA doesn't rise with boost, fuel pressure does. FPDA is a constant number with slight variation and is basically your base fuel pressure. It will fall thou with loss of fuel pressure showing the actual difference. Log FP, boost and FPDA and you will see where the pressure is falling off and you will see FPDA starting to fall. See if you can pinch/block off the return line and cycle key to see if the system holds pressure when primed.
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