Fuel Pressure drops, car stalls. Could it be the Fuel Pressure Valve ?

Hi all, I am new to this forum.

I recently bought a used Mazdaspeed 3, after about 600 miles of driving it around to work and during the week-ends, it stalled after about an hour of driving and I couldn't start it again. I had it towed to a safe parking spot and got back home where I have a second car.
2 days later, went back to the Mazdaspeed, started it, and it worked like a charm. Replaced the Fuel Pressure Sensor, but no dice (used this reference Bosch 0 261 545 053, it works fine).
Hooked up a generic OBD II adapter and read several PIDs (don't have an AccessPort), and it appears that the rail fuel pressure drops before stalling after driving it around for half an hour and idling for a while.
At WOT, fuel pressure goes up to 1800 psi, at idling, it's at about 400 psi, everything seems fine, but after letting it idle for a while and stopping it, I saw that the KOEO fuel pressure would climb very slowly from 400 psi and that it never got up to more than 900 psi.
If I let it idle and then stall for even longer, KOEO fuel pressure stays at about 40 psi (ITFP).
Of course, no DTCs whatsoever.

I suspect the Fuel Pressure Valve is shot, but could it be the reason the fuel pressure drops "randomly" causing the car to stall ?
Car is still under warranty, so I won't change parts myself but I will keep you updated so people that have the same issue as me can look it up.

Year/Make/Model: 2008 Mazdaspeed 3 (Mazda 3 MPS)
Mileage: ~100k miles
Location: France
Concern: Fuel pressure drops then car stalls
DTC's: None
Modifications: Unknown
Is the concern intermittent? Yes
Can you duplicate the concern? Yes, after about 30 min of driving
Recent Repairs: Turbo CHRA and o-rings
Correction: Fuel pressure sensor

 

As far as the PRV being bad you should conduct this test with a hot motor ideally. @Sho did us a favor and made this video!



Since you don't have an Accessport for data logging I would suggest you look into Forscan. It will allow you to capture real time data and then go back and look at what's happening with your fuel pressure or any other PIDs you select.

Forscan has a mobile app for Android and Apple and can be used via Bluetooth OBD adapter.
https://forscan.org/faq.html#licensing

If your PRV is failing it should become evident via data logs with fuel pressure behavior or the results of the test in the video. Also a failing PRV can make a lot of noise that will sound like it's coming from your HPFP because of the location of the PRV being directly below it.

 

Hi, thanks for the headsup about forscan, will definetely install it next time I get to the Mazda.

The PRV is definetely failing, since the KOEO fuel pressure doesn't go up to the expected 1850 psi before opening.
When the car is hot, the KOEO fuel pressure sometimes decreases instead of increasing.
I don't hear any specific noise, but I'm still new to the car so I guess I could be missing something.

Do you think a failing PRV could cause the car to stall this way ?

 

When you say "stall" do you mean that the car shuts off entirely or that it stays running and stumbles?

I dealt with a few issues last summer one being a failing PRV.

My PRV was making noise, fuel pressure at idle was in the mid 200s psi, at WOT fuel pressure would tank into the 800s psi around 4k RPM.

So yes it can and will most likely cause poor drivability issues from my experience.

 

Lack of fuel will certainly cause the car to stall, whether or not it's the only issue at hand is a different matter but with the failed PRV test it's time to change the PRV valve. Start there