External Fuel Regulator

[Schemxr]

So i have a stage 4.5 lpfp from precision raceworks and it comes with an external fuel regulator. this regulator is supposed to be set to 72psi with the secondary pump manually activated which i have done already.

however there is also a 1 to 1 boost reference port on the regulator, the instructions say to leave it to atmospheric pressure or connect to a boost reference but never to keep it blocked off.

when i was in twin turbos, whoever installed my lpfp blocked the boost reference port on the regulator, eventually after 2 years, the secondary pump finally failed and I had to send it out to precision for repairs. once i got it back, i re installed everything and set the secondary pump psi to 72. based on the instructions i left the boost reference pirt open to atmosphere. however now, when i am about to do a pull, my LPFP Act data on my datalogs shows my psi drops to 58-59psi before going past 13psi of boost at which point the fuel pressure goes back up to 72 since my hobbs switch activates my secondary pump.

my question is does anyone know why thag is? am i supposed to connect the boost reference port on the regulator to a boost reference source from somewhere in the engine bay?

my tuner recommended me trying to tap into the tmic which i bought the adapter waiting on delivery but was wondering if anyone else had this experience and what they did to solve it.

[Wanted_M]

IMHO, you're running out of fuel as the engine load/boost pressure starts to build. Are your leaning out on the logs during that transition? What's the AFR, STFT, fuel rail pressure and timing say vs fuel @72psi?
I would lower the Hobbs switch to 10-11psi, that way secondary pump kicks in earlier and allows you to maintain the full 72psi range and it might go a little higher, but it will level off due to boost. You're basically catching a dead spot within the transition as your primary pump is tapped out and secondary making up the loss. IIRC, if you tap into the IC or J pipe the fuel pressure regulator becomes a rising rate fuel pressure regulator 1:1 and that's not what you want hence why you leave it open, so it controls based on set screw @ 72psi. It's been a while since I've messed around with regulators but hopefully my response helps.

Anyone else can chime in and let me know if I'm wrong. Good luck man and keep us posted on how you resolved it.

[Schemxr]

Originally Posted by Wanted_M

IMHO, you're running out of fuel as the engine load/boost pressure starts to build. Are your leaning out on the logs during that transition? What's the AFR, STFT, fuel rail pressure and timing say vs fuel @72psi?
I would lower the Hobbs switch to 10-11psi, that way secondary pump kicks in earlier and allows you to maintain the full 72psi range and it might go a little higher, but it will level off due to boost. You're basically catching a dead spot within the transition as your primary pump is tapped out and secondary making up the loss. IIRC, if you tap into the IC or J pipe the fuel pressure regulator becomes a rising rate fuel pressure regulator 1:1 and that's not what you want hence why you leave it open, so it controls based on set screw @ 72psi. It's been a while since I've messed around with regulators but hopefully my response helps.

Anyone else can chime in and let me know if I'm wrong. Good luck man and keep us posted on how you resolved it.

not leaning out at all, i attached a log below
https://bootmod3.net/log?id=663c6807e9bc091026be9d96

[-Eidos]

Originally Posted by Schemxr

So i have a stage 4.5 lpfp from precision raceworks and it comes with an external fuel regulator. this regulator is supposed to be set to 72psi with the secondary pump manually activated which i have done already.

however there is also a 1 to 1 boost reference port on the regulator, the instructions say to leave it to atmospheric pressure or connect to a boost reference but never to keep it blocked off.

when i was in twin turbos, whoever installed my lpfp blocked the boost reference port on the regulator, eventually after 2 years, the secondary pump finally failed and I had to send it out to precision for repairs. once i got it back, i re installed everything and set the secondary pump psi to 72. based on the instructions i left the boost reference pirt open to atmosphere. however now, when i am about to do a pull, my LPFP Act data on my datalogs shows my psi drops to 58-59psi before going past 13psi of boost at which point the fuel pressure goes back up to 72 since my hobbs switch activates my secondary pump.

my question is does anyone know why thag is? am i supposed to connect the boost reference port on the regulator to a boost reference source from somewhere in the engine bay?

my tuner recommended me trying to tap into the tmic which i bought the adapter waiting on delivery but was wondering if anyone else had this experience and what they did to solve it.

Since the original secondary LPFP died, you've moved from twins to single turbo? Same secondary pump was installed? And now you're seeing LPFP act drop? Are you DI-only or running PI now?

There seems to be a few moving parts here that should be cleared up before we can help answer your question.

[Schemxr]

Originally Posted by -Eidos

Since the original secondary LPFP died, you've moved from twins to single turbo? Same secondary pump was installed? And now you're seeing LPFP act drop? Are you DI-only or running PI now?

There seems to be a few moving parts here that should be cleared up before we can help answer your question.

ok so i had the 4.5 on my twins, then i went to single turbo, secondary failed after a few months and now it’s fixed so i installed it.

port injection running via motiv reflex with the precision racing system. oem eu5 di as well. fuel regulator set to 72psi with secondary pump running manually. 1 to 1 left open to atmosphere.

LPFP Act psi is 70-72psi at idle (primary pump i’m assuming)

same secondary pump as before walboro 525 and oem primary pump


before when i was on twins, whoever installed the pump and the regulator used a bolt to block off the 1 to 1 on the regulator.

now what i’m seeing is before my hobbs switch activates the secondary pump, my lpfp act psi drops to 58-59psi before it spikes up again above 72psi because the secondary gets activated.

however even when the lpfp act drops to 58-59, my hpfp target and hpfp act is stable and not dropping, my STFT’s are relatively fine arounf 1.0 and my AFR’s are not leaning out. so i’m not sure if this was normal this whole time or if it’s because the 1 to 1 is no longer blocked off as it was before when i was on twins. back then i was tuned by f80paul and now on single turbo i have a different tuner

[Schemxr]

updated: diaphragm in fuel regulator seems to be ruptured, fuel slightly leaking from 1 to 1 boost reference port. going to switch out the diaphragm and see if the lpfp act still drops under throttle until secondary pump kicks in.

if it still drops then going to try to connect the reference port to a boost tap on the tmic and if it still drops then i will cap off the boost reference port.