[SOLVED] HPFP Issue (in-tank pressure)

Update 3/1/2022: This issue has been resolved. Spill valve was responsible for 60psi drops and PRV was responsible for for fuel pressure never exceeding ~1700psi.

Year/Make/Model: 2008 Mazdaspeed3
Mileage: 160K chassis / <1K motor
Location: AZ
Concern: Fuel pressure drops to in-tank pump pressure
DTC's: None
Modifications: BNR S3v4, catless downpipe, CS internals, 3in intake, FMIC, etc
ECU/Tuning Software: Accessport V3
Tuner: DramaTuned
Is the concern intermittent? Yes
Can you duplicate the concern? I believe so
Recent Repairs: Replaced HPFP internals
Correction: CS HPFP internals

Hey everyone, I've been chasing a HPFP issue for a while now and wanted to start a thread since it seems to keep coming back. I'll give a brief timeline, as this issue may be from before my motor swap and I'm just now aware of it.

• OEM motor popped at 160K
• New OEM motor installed
• Driving great during break in, no boost, etc
• First few WOT pulls after break in were great
• Then WOT pulls break up and show fuel pressure dropping to ~60psi briefly
  
• Swapped out pressure relieve valve with new OEM one ("old" one was only ~18 months old)
• Fuel pressure issue persisted, so I reinstalled my "old" one as it had a CS stainless filter
• Ruling out the PRV, I had my unbranded HPFP internals replaced with new CorkSport ones
• Issue gone for the last 3 days, pulls hard, etc
• Random city driving today and the pressure drops to ~60psi and seems to stick there as long as there's a minor amount of load
• Got a few data logs and am making this post

I've attached a data log that I recorded right after experiencing the issue. At this point the only next troubleshooting step I can think of is checking the wiring to the spill valve.

 

Shot in the dark here. Have you checked the HPFP ground?

 

I checked what looked to be the ground for the HPFP, if it's a little black wire coming from a the harness and going to the metal plate that holds the connectors. It looked alright to me.

 

I'm not a wiring expert, but I did test for continuity and resistance for the spill valve. With the ECU disconnected, I tested the terminals on the spill valve as well as the connector on each end, spill valve to ECU.




Spill valve terminals: 1.8Ω
Green to Yellow: 0.5Ω
Red to Red: 0.5Ω

Everything seems to be okay, so I'm not sure if that would lean more toward the spill valve itself being bad or the ECU.

 

Any way you can load test the wires between the spill valve and ECU? I like that you used the diagnostic sheet I made as it helps to see everything laid out and is easy to read.

You can have one or two strands of wire and see low resistance but if there is excessive corrosion or a bad wire it won't carry the current required.

FWIW my speed did the same thing and it turned out to be corrosion at the ECM connector. I had to remove a pin for the spill valve and solder a new pin with lead in it's place. If that is the cause I still have the old spare connector and can send you a pin with a lead no charge.

 

If it's something I can perform with basic tools and instructions, I'm willing to give it a shot. At this current point, aside from testing for continuity and such, I'm planning to see if cleaning the spill valve has an effect on the issue. If it acts better next time I drive it, I'll buy a new HPFP and swap the spill valve over. If I'm able to test and determine it's a wiring issue, then I'll figure out exactly how to repair the issue and go from there.

Is there anything else I might be missing? The sensor on the fuel rail hasn't been touched, but because it's always reading pressure, never 0, I assume it's working as intended and my problem lies within the HPFP itself and/or pressure relief valve out of the rail.

 

Cleaning spill valve is a good call.

To be clear during wot you are having power cut right,? If not it's probably the sensor dying or poor connection to the girl pressure sensor

 

Yes during WOT the car has hit 60psi and hesitated. I haven't seen it happen under vacuum, but it happens even at small boost levels.

 

https://mazdaspeeds.org/index.php?threads/how-to-diagnose-thread.12295/

Check this out for electrical diagnostic information.

 

Great post! I'm much better with visuals, so could you double check that this is what you advised in the write up?



Also wanted to provide an update in that cleaning the spill valve did not seem to change anything. I saw my fuel pressure drop to in-tank pressure on the drive after cleaning unfortunately.

Next up is electrical connection, potentially load testing, and swapping out the spill valve with another one.

 

Update, I did the diagnostic procedure as @L337TurboZ mentioned and the bulb illuminated just fine, flicking at times because of me touching the wire to the battery I assume. Since this is specifically for load and I've already tested for continuity, I assume the wiring all checks out unless there's an intermittent short somewhere.

I guess my next step will be to replace the spill valve?

 

Another update, I redid the bulb test this time with the positive wire stuck into the socket for more than a moment while I wiggled the harness around. The bulb stayed lit the entire time as I jostled all the connectors and loom around, so I think I can safely rule out the wiring harness being the culprit.

I'm picking up another HPFP assembly today. I'll try swapping over the spill valve first, then will use the housing if that doesn't work.

 

Providing another update. I've been waiting to post until I had fixed the issue or had something concrete, but you'll see that's not the case here.

So I swapped spill valves from the used HPFP assembly I picked up and unfortunately still saw the issue. I then swapped my CorkSport HPFP internals into the used housing that I picked up and the car ran great! There was still some hesitations during WOT, so I decided to swap the secondhand spill valve back over. With a secondhand HPFP housing and spill valve, I was feeling great as the car was running pretty well, but not perfect. Since I didn't spend any time cleaning the "new" HPFP as I was just testing it, I pulled the secondhand spill valve back out and cleaned that up. I threw that back in and drove around seemingly without issues until randomly at 70mph on the freeway my fuel pressure dropped to ~40 and then slowly rose back up as I coasted off the freeway.

I'm kind of lost as to what could be going on here, but I know the spill valve plays the most important role as it's the only thing electrical on the fuel pump.

 

That's very peculiar, 40 psi now? That's less than itfp pressure sounds like it's that pump going out.
Before diving into that @Enki / @JohnnyTightlips please help you're definitely our fuel pump gurus.

 

I wouldn't rule it out, but that was just the minimum value I saw. When this happened on the freeway it was holding the usual 60psi or so and then creeped back up into the hundreds and eventually around the ~400psi idle target.

I also spent $10 on the wiring diagrams for the Mazdaspeed 3 hoping it would contain the PCM, but it did not. My loss is anyone's gain I suppose.

All Wiring Diagrams for Mazda 3 Mazdaspeed 2008 model (1.6Mb)

 

Ooh man for a 10$ donation here you could have gotten access to it (wiring) and the shop manuals, we have them all in the metal member section, thanks for the file though

Edit: seems we didn't actually have the gene wiring diagram listed, that I could see atleast could have missed it I'll add this one to that section.

 

That's good to know. I don't necessarily like the idea of the members section on here, but I'm happy to contribute!

 

Well being a member comes with benefits like being able to enter raffles, get diagrams, buy/sell etc.

I once won a raffle and got some cool stuff! It also helps support this community. Definitely worth it.

 

I'm sure it's absolutely worth it! I also don't mind supporting communities, but I simply don't like the idea of information being hidden by a paywall. Had a really bad first experience with that on these forums when I first posted here.

 

absolutely diagrams, monthly raffles (atleast a $50 MSO vendor gift card of your choice, have seen steering wheels, exhaust manifolds, engine dress up kits (adapted performance donates a lot)). It's also where we have the for sale section.

None of the diagnostic threads or information threads are in the members section that'd all public access.

Gotta keep the lights on somehow and that's through vendor fees and member donations.
Edit:
Keep in mind were not MSF that "donate or we won't help you Brownie" attitude isn't here