I currently have p0175 and have had p0172 in the past as well. I wanted to start troubleshooting to fix this. I was gonna start by checking fuel injector balance, but immediately noticed that when I turned key on the pressure was over 100 psi! While running it's 95 psi. This seems wrong. Where should I look? I replaced the fuel filter/ regulator recently. My car is a stock 6spd 2001 with 91k miles.

 

My first thought would be to check the gage. Mind, I'm not really certain how I would check the gage. Preferably against a known good source -- though I'm not sure what that would be. I have the HF test set, haven't used it yet. If it read 30 psi high on the corvette, I'd see if I could check the Subaru and see if it, too, read questionably high.
I wonder if the gage would read compressed air pressure. That might increase chances of getting additional sources and verification methods.

 

Where did you buy your filter/pressure regulator ??…if Amazon or EBay may be a good idea to buy from a reputable source…high fuel pressure can set those 2 rich DTC’s.

 

most common would be gauge is bad/wrong or clogged return line / failed regulator

 

 

Not sure about your car but most LS Corvettes has a "fuel bypass system " that re directs over pressure back into the fuel tank If your car has a bypass Check it out It may have a clogged line

 

Gauge is brand new. I ordered another filter/regulator even the the current one is basically new. I’ll report back once it’s installed

 

Confirm with mechanical pressure gauge on fuel rail.

Replace filter/regulator with OEM Delco one.

 

I assume you mean "fuel return" .......

 

spring regulation, 'bypass' regulators
All over-valve injection cars have return fuel regulators aka bypass regulation, and a return pathway "line" even the ones labelled 'returnless'. The returnless part only refers to the engine rail, and usually the part of the vehicle where the engine is. This is done to reduce complexity/expense at the cost of performance and fuel system longevity. I always recommend when tuning any over-valve injected engine, relocating the regulator to near the engine so you can use a referenced regulator and reduced fuel pressure to reduce fuel/wiring heating, reduce fuel pump current draw, increase fuel pump flow rate and life span. That is a bunch of benefits that should not be overlooked in any performance application for daily drivers which sit in traffic and could use that relief.

non-spring regulation
Direct injected engines are the only ones I am aware of that can be truly returnless. There is a fuel computer dedicated to the frequency response of the fuel pump, monitoring state space vector of engine demand from the main computer and for fuel flow using an particular in-line sensor often positioned at a specific angle in the fuel flow. The fuel computer is able to produce a PWM signal for the fuel pump which provides the exactly correct amount of fuel pump angular velocity & acceleration / time to maintain a set fuel pressure. A traditional spring regulator like the ones we use in over-valve injection is said to respond too slowly to meet the sudden demands of high pressure direct injection secondary pumping, as it has a second high pressure pump making thousands of psi

 

I replaced the wix filter that was new 11/24 with a delco. My pressure is about 62 now so assume that’s more normal and I got unlucky with a defective wix filter. Interestingly, both are marked made in Taiwan. Hopefully p0175 goes away now.

 

Good news !!

 

Yes fuel return some call it a by pass

 

Same thing happened to me installed Wix 33737 filter. Driving a day later got codes 172/175 rich condition. Replace the garbage Wix with another brand all good.