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.

 

[SpeedForThee]

I just went through and chased the hpfp connection as far as I could and didn’t see any breaks or damage to it. I put some dielectric grease on the connector and zip tied it to the spill valve, right after pulling out of the driveway the fuel pressure dipped down to 58 psi. I still have no evidence of an external fuel leak via smell or sight but I’m not ruling it out. Maybe I need to put my phone in the engine bay and drive around… I could verify the hpfp not functioning when the pressure drops by hearing it on a recording… maybe I’m just going crazy from pulling the factory battery box and intake off so many times. Next step will be the relief valve, fuel pressure sensor and fuel line to fuel rail o rings whenever they eventually ship out. In the meantime I’m waiting on Bezos to deliver my mini USB cable so I can upload the logs.

 

[Enki]

No the HPFP will absolutely click when it's working. It seems likely that it's either electric (check with meter), internals sticking, or PRV failure.

 

[SpeedForThee]

So I did indeed just skip around the neighborhood with my phone tucked in between the ECU and the battery… the hpfp makes happy tractor noises the entire time, even when the fuel pressure drops. So the hpfp seems to at least not be completely losing signal according to my redneck math. I guess I wait for the prv to show up.

 

[SpeedForThee]

Bezos delivered my cable today, here's a couple of data logs. These are from simply trotting down the street and back so very light throttle. On my APv1 I can only monitor one thing at a time so it's nice to finally be able to see all of the data together. Nothing really sticks out like a sore thumb to me... apart from fuel pressure. I ordered the PRV, fuel pressure sensor, and high pressure fuel line to fuel rail O rings last Monday and still haven't gotten a shipping notification, I'll try to get an update from them tomorrow.

 

[Enki]

If you had a fuel leak in the bay, I'm pretty sure you'd smell it.

 

[SpeedForThee]

That's my thought as well, I've even thrown a few microfibers around the fuel rail to see if they pick up any fuel scent but nada. I have an entire spare HPFP housing, I guess it wouldn't hurt to throw the OEM internals into that and see what happens. Tornado watch all night tonight and the sideways rain showcases how shoddy this rental garage is, I'll get to that tomorrow most likely. By the end of this I'll have a sick new intake... it's almost inevitable that I break the vacuum nipple off the factory one.

 

[Easter Bunny]

Get a new hose and slice the old one off the nipples

 

[SpeedForThee]

I still maintain that I had no fuel smell in the engine bay but remember this is the Internet and I could be a complete idiot. I decided to go all the way again, this time pulling the fuel rail off for funsies. The o-ring on injector number three has a funky shape to it, I’d say it’s more ovular and potentially pinched or blown out. I’ve handled a few injectors in my day but could someone back me up here? The o-rings on the other three injectors were still circular. Hopefully it comes across in these shitty pictures. I don’t mind spending another $12 on a set or even $50 on all four if the internet thinks so.

 

[Easter Bunny]

looks a little off but if it was pushing out enough fuel to make a difference in how the car was running you would be able to smell it

 

[Enki]

It really doesn't take that much of a gasoline leak for you to be able to tell smell wise. That shit WANTS to be a vapor and to spread out. If it's not windy, a couple of drops would be detectable.
If it's going into the oil, however... Maybe pull the dipstick and give it a good ole sniff (after a hot drive). Should be no fuel smell in it if you're using a good oil.