Should I replace my PRV?

Doing tuning for my down pipe and Tuner noticed my fuel rail pressures are low. I have been watching them for the last week and they are low and kind of all over the place. Idle is about 450-600. Cruising on the highway is about 1500. If am idling (about 450-600psi) and I blip the throttle, pressure goes to 1500-1750. WOT is MAYBE 1600 but it kinda jumps around.

Background: Once tuner noticed pressure was low, he recommended I pull/clean HPFP... so I did. I found a nice clean and spotless HPFP (including the internals). I saw no abnormal wear. I just cleaned my HPFP and installed all new O-Rings. I pulled my dump valve and it was spotless. Car runs OK. It does miss/surge some at WOT. No CEL at all. LTFT is kind of all over the place between 4 and 12

Should I suspect my PRV? My fuel pressure sensor? Could it be the little filter on the rail?

 

What if the spring on the HPFP has gone bad? Could that be possibly reducing the stroke of the HPFP and therefore the volume? I found a stock HPFP for $90 and am going to pick it up. If that does not cure my ails, I guess I will do a PRV and pressure sensor. Any thoughts?

 

Couple things.

1. Did you break the spill valve down and clean/lube it when you replaced the o-rings?
2. Have you done the PRV test where you get the motor nice and warmed up and then shut the car off but leave the key on to see if the pressure climbs up to ~1850 and then drops?
3. How many miles on the car?

I had an issue with pressure at WOT dropping a bit too much for my liking with brand new CS internals (so a new spring) and freshly rebuilt pump with new o-rings. I replaced the PRV, partly just for preventative maintenance (my car has about 200k miles on it) and that didn't fix it. But then I realized that the CS instructions for their o-ring kit don't have you disassemble the spill valve all the way. After doing that and cleaning/lubing it (it didn't even seem too gunked up) and reassembling it, my pressure drop at WOT went away.

 

I did open up the spill valve and clean it. No change.
I did try the PRV test where I run it, shut it down but leave the key on. I never got over 1600 psi on the test.
I have 140k miles.

 

Does it fail the test? Yes? Replace with new OEM one

 

Well this sucks. I ran the test and it failed at 1550 psi. So I ordered a new PRV from Japan (factory part), waited 3 weeks for it to get here, installed it, it passed the test this time cracking open at 1805psi (although it did take a long time to get there). Started my car and pressure dropped to 380psi. Took it for a spin and never saw over 1500 psi during the drive. WOT starts at 1100'ish and as RPMs rise, pressure drops. I get scared when I less than 1000psi so I back off.

Just to recap, I have tried two spill valves (both nice and clean) and replaced the PRV. I replaced the tiny filter that is on the low pressure side (the little tiny one in y block on the side of the HPFP) but is there another one I should check? I also tried two different check valves.

Looking at this:
https://corksport.com/blog/hpfp-troubleshooting/
I guess I will call Corksport tomorrow and ask them for advice, too, since I am running their O-Ring kit in my HPFP.

 

That's irritating sorry it's not working out sounds like you've got multiple things. There is the little fuel filter in the PRV (which would have been fresh with a new valve) and one on the hpfp, those are the two you see in the kit.

You rebuilt the hpfp with the CS kit? So I presume the spill valve is fully cleaned I wonder if the internals are sticking? I know @Raider had his fail and replaced them but I don't remember what the symptoms were.

 

I did use the CS Kit. Both spill valves I have used have been cleaned IAW the fantastic instructions that came with the CS kit and this thread
https://mazdaspeeds.org/index.php?t...nd-spill-valve-michael-rey-facebook-kit.8069/

Wait..... looking at that thread... Looking at the disassembled spill valve pic... (hopefully my pirated pic comes through)...
The ridge pointed at by the red arrow and the C-Clip that holds it in marked by blue... Does the C-Clip go into the green side of the ridge (where I put it both times) or the yellow side? It didn't seem to want to fit on the yellow side.


Also, when I torque, actually just tighten down, the spill valve retaining nut, how tight should it be? I can turn the spill valve with big crescent wrench but not by hand. Could I have it overtightened?

 

Should be snug in there I don't exactly recall how the little valve fits in, I remember having some issues too.

@JohnnyTightlips any advice for this man?

 

OK, so last night after the last post, I backed off the spill valve retaining nut about 1/8 of a turn. Today on my way to work my pressure seems better. I can’t say it is good yet, but it is better. I saw 1700 and 1800 psi register on my access port a few times. Hopefully on my way home from work today I can get some data logs and really look at it.

 

YASSSS!!! Log looks good! Put about 50 miles on it over the last couple days; at WOT pressure maintains over 1650 the whole time!!
So, I think, my PRV was bad and I over-torqued my spill valve. Pulled some logs and sent them to Justin/Freaktune so I can finish up a DP tube for 91 octane, then tune for corn!!

 

Hey man,

I'm glad to see you got your issue sorted. Have your fuel trims stabilized now that you've replaced your PRV?

Mine fails the test, but is not completely broken and my fuel trims are completely wonky. I've spent a lot of my own time troubleshooting and paid a shop to troubleshoot (they found a few boost leaks), but I still have the issue.

I've ordered a new PRV...fingers crossed this solves my issue too.

Next spring I plan to pull the HPFP to clean it, the spill valve and replace the o-rings as well.