HPFP or LPFP issue

azul89 · 09-06-2023, 02:38 PM

I have 13k miles on my VB. Under WOT i lose fuel pressure, but if I gradually accellerate no issues. If I never floored the car I wouldn't even notice it. I have a log of the fuel pressure drop. How can I figure out if its LPFP or HPFP related?

* Registered users of the site do not see these ads.

uglywrx · 09-06-2023, 04:51 PM

HPFP is mechanically driven off a cam, there isn't really much to go just a little bit wrong. The low pressure pump has more things that can go wrong with it, and is a cheaper and easier fix. It could be as easy as just having a clogged filter honestly. You could also take the cover off the head and see if there is any glitter or debris in there.

Also I'm guessing you voided your warranty?

uglywrx · 09-06-2023, 04:51 PM

HPFP is mechanically driven off a cam, there isn't really much to go just a little bit wrong. The low pressure pump has more things that can go wrong with it, and is a cheaper and easier fix. It could be as easy as just having a clogged filter honestly. You could also take the cover off the head and see if there is any glitter or debris in there.

Also I'm guessing you voided your warranty?

Apb_pools · 09-06-2023, 07:32 PM

Lower ethanol content et voilá. I havent had a hiccup since going e50-60 exclusively. Hope it works out.

Elbert Bass · 09-07-2023, 09:32 AM

The truth is that the HPFP has a bleed valve controlled by the ECM to modulate high fuel pressure to the injectors. Compare the target fuel pressure to the fuel pressure sensor reading. Any difference could indicate a faulty pump or sensor. A lean condition with lower actual pressure would indicate a HP pump fault.

As far as diagnosing LPFP - install a fuel pressure gauge on the LP fuel line and monitor while driving. If you see the pressure drop below 45-49 PSI (WRX) you have have a LP issue. A flow volume test result of less that 39 gal/hour could also confirm an issue with the LP pump/filter. LP fuel pressure/flow test values at minimum 12 volts.

azul89 · 09-07-2023, 12:19 PM

Quote:

Originally Posted by Elbert Bass

The truth is that the HPFP has a bleed valve controlled by the ECM to modulate high fuel pressure to the injectors. Compare the target fuel pressure to the fuel pressure sensor reading. Any difference could indicate a faulty pump or sensor. A lean condition with lower actual pressure would indicate a HP pump fault.

As far as diagnosing LPFP - install a fuel pressure gauge on the LP fuel line and monitor while driving. If you see the pressure drop below 45-49 PSI (WRX) you have have a LP issue. A flow volume test result of less that 39 gal/hour could also confirm an issue with the LP pump/filter. LP fuel pressure/flow test values at minimum 12 volts.

Thank you. I went ahead and ordered the Fuel-it LPFP because I wanted to upgrade that anyways. If there was a performance HPFP available I would go a head and switch to that as well. Just because, but I am not about to drop $600 on oem unless I have to. Thank you for the tip. It hasn't happened again since I reflashed the car. It might have something to do with the fuel pressure sensor...Thank you I have a better perspective now.

richilg1 · 03-06-2025, 12:09 PM

Quote:

Originally Posted by azul89

Thank you. I went ahead and ordered the Fuel-it LPFP because I wanted to upgrade that anyways. If there was a performance HPFP available I would go a head and switch to that as well. Just because, but I am not about to drop $600 on oem unless I have to. Thank you for the tip. It hasn't happened again since I reflashed the car. It might have something to do with the fuel pressure sensor...Thank you I have a better perspective now.

So you were running high ethanol content?

09-06-2023, 02:38 PM	#1
azul89 Scooby Newbie Member#: 123491 Join Date: Aug 2006 Chapter/Region: South East Location: Hickory, NC Vehicle: 2022 WRX WR BLUE	HPFP or LPFP issue I have 13k miles on my VB. Under WOT i lose fuel pressure, but if I gradually accellerate no issues. If I never floored the car I wouldn't even notice it. I have a log of the fuel pressure drop. How can I figure out if its LPFP or HPFP related? * Registered users of the site do not see these ads.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

09-06-2023, 04:51 PM	#2
uglywrx Scooby Newbie Member#: 534505 Join Date: Jun 2023 Location: PA	HPFP is mechanically driven off a cam, there isn't really much to go just a little bit wrong. The low pressure pump has more things that can go wrong with it, and is a cheaper and easier fix. It could be as easy as just having a clogged filter honestly. You could also take the cover off the head and see if there is any glitter or debris in there. Also I'm guessing you voided your warranty?

09-06-2023, 07:32 PM	#4
Apb_pools * Banned * Member#: 534487 Join Date: Jun 2023 Location: Arizona, USA Vehicle: 22 WRX	Lower ethanol content et voilá. I havent had a hiccup since going e50-60 exclusively. Hope it works out.

09-07-2023, 09:32 AM	#5
Elbert Bass Scooby Specialist Member#: 283429 Join Date: May 2011 Chapter/Region: South East Location: Down yonder. Vehicle: 2016 Crosstrek Silver	The truth is that the HPFP has a bleed valve controlled by the ECM to modulate high fuel pressure to the injectors. Compare the target fuel pressure to the fuel pressure sensor reading. Any difference could indicate a faulty pump or sensor. A lean condition with lower actual pressure would indicate a HP pump fault. As far as diagnosing LPFP - install a fuel pressure gauge on the LP fuel line and monitor while driving. If you see the pressure drop below 45-49 PSI (WRX) you have have a LP issue. A flow volume test result of less that 39 gal/hour could also confirm an issue with the LP pump/filter. LP fuel pressure/flow test values at minimum 12 volts.