Fuel pressure dropping to ITFP levels while driving

[SpeedForThee]

Year/Make/Model: 2008 Mazdaspeed3
Mileage: 108k
Location: WI
Concern: Fuel pressure drops to in-tank pump pressure while driving
DTC's: None
Modifications: Autotech HPFP internals
ECU/Tuning Software: Accessport V1 (used only for datalogging when in need)
Tuner: Stock
Is the concern intermittent? Very frequent
Can you duplicate the concern? Simply by driving around
Recent Repairs: HPFP internals, Corksport O-ring kit, CWTurbo injectors with Overspeed seals and GB O-rings
Correction: Double checked injector job, recleaned entire HPFP and internals, swapped spill valve

Long time lurker, first time poster here!
- Two weeks ago I picked up my car from storage and installed Autotech HPFP internals along with Corksport's O-ring kit, everything was cleaned with Naphtha and lubed with Redline as per the forum wizards.
- I then drove the car 500 miles home without a single problem.
- I parked the car for a few days and got around to swapping in some cleaned/flow tested injectors from CWTurbo along with Overspeed seals and GB manufacturing O-rings.
- I replaced all gaskets along the way, however I did not replace the HPFP line to fuel rail O-rings as it seemed to be in good shape
- Now then... the car idles fine with HPFP actual at ~430psi. I can blip the throttle and it'll climb to ~1800psi as it should. Once I get driving the fuel pressure consistently stays above 1000psi as it should... until it doesn't.
- It seems if there's any load on the engine (slightly increased throttle or even going up a small hill) the HFPF actual immediately drops to ~60 psi and remains there until I let off the throttle. KOEO pressure reads at 60psi.
- I've gone back and double checked my work on the injector job and found nothing leaking, no fuel smells, nothing weird. I've re-cleaned the HPFP housing and swapped spill valves with a spare I have, no change.

I really don't think it's a HPFP problem as I drove the car 500 miles home without a hiccup, I didn't have problems until I touched the injectors. I'd love to be told I'm wrong, however. I see similar posts that were solved with a new spill valve but I don't seem to have that much luck. Is there anything past the HFPF that could cause rail pressure issues? I have some logs to attach but I can't seem to find the correct USB cable for this dinosaur of an APv1 so I'll have to go out and buy one.

 

[Easter Bunny]

Need to get the motor hot and test the prv

@Enki help

 

[Enki]

What engine oil and fuel are you running?
Also, there are really only a couple things it could be for the pressure to just insta tank like that:

1. PRV sticking open
2. Spill valve not actuating properly and/or the spring under the button sticking (if you squeeze it and it sticks together, that's a problem)
3. Internals sticking for some reason

I ask about the oil and fuel you use because bad oil or just improper cleaning can result in insane buildup of one or more of the "deaths" (black death and sticky death, both bad, both obvious).

See attached for how bad the sticky situation can be (the entire button assembly was just pressed to the lighter fluid bottle).

 

[SpeedForThee]

I had considered testing the PRV but I don’t really want to drive the car around long enough to get up to 220 and I’m not sure it’d get there idling. To be cautious I did order an OEM one on Monday, still waiting on it to ship out. I also ordered a fuel pressure sensor and the HPFP line O-rings to just to complete the parts cannon.

To answer Enki, I’m running Penzoil Platinum 5w-30 and nine times out of ten I’m filling up with Shell 91 (not much 93 up here, also non ethanol). I did replace the spring and button when I swapped spill valves, here’s the clean ones that aren’t in the car. To my eye they are spotless and the spring is definitely not sticky. I’ve also dicked with how tight the spill valve is since there’s no real way to torque it, no change.

 

[Enki]

If you use your thumbnail to actuate the spill valve needle, is it sticky or does it move without any felt hesitation?

 

[SpeedForThee]

The needle seems to move in and out freely, no hesitation. Again it’s just odd to me that I had no problems until I swapped the injectors. it really makes me think it’s something I did but the fuel pressure dropping to tank pressure points to the hpfp.

 

[Enki]

Could be electrical too. All it would take is a loose connection on the spill valve and bam, ITFP pressure.