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Adjustable FPR - should FP drop to zero once vehicle is turned off?

Discussion in 'Technical Chat' started by redneck_adjacent, Oct 22, 2023.

  1. Oct 22, 2023 at 11:22 PM
    #1
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    I recently installed the TS-0401-1102 in my 1997 Toyota Tacoma DLX 4x4 with 2.7L. I adjusted the regulator to 45 PSI without vacuum reference per the instructions. The gauge connected to my fuel pressure regulator (TS-0402-2023) reads about 35 PSI once vacuum reference was applied, which matches what I normally see on this engine. The truck runs great. However, I have noticed two things which puzzle me: the engine takes a long time to turn over with this fuel pressure regulator, and fuel pressure drops to zero immediately after the engine is turned off. Are these symptoms normal? To clarify, my fuel system has no leaks. The only thing I can think of is possible vapor lock; however; this issue seems persistent no matter what.
     
  2. Oct 22, 2023 at 11:27 PM
    #2
    Speedytech7

    Speedytech7 Toyota Cult Ombudsman

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    Fuel pressure should not drop to zero immediately after the engine is turned off. Could be a bad check valve in the fuel pump or perhaps you have an injector that stuck open. Sounds like the regulators working fine. Earlier model tacomas use a vacuum switching valve to change whether the fuel pressure regulator sees manifold vacuum or atmosphere. I have a feeling this could affect cranking times on a stock computer if it's expecting full pressure during startup but it's getting vacuum referenced pressure instead. Just food for thought... You'll have a longer crank anyway if it has to rebuild fuel pressure every time so I'd start chasing that first
     
  3. Oct 22, 2023 at 11:32 PM
    #3
    Speedytech7

    Speedytech7 Toyota Cult Ombudsman

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  4. Oct 23, 2023 at 12:00 AM
    #4
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    Thanks, Zane.

    For what it’s worth, the OEM FPR did not cause this long-start symptom so I don’t think it’s the injector(s). Also, both FPR’s - the OEM and adjustable - are referencing vacuum from my supercharger. Maybe I am missing something but I am not seeing how the VSV would be responsible.

    I did some research online and it sounds like adjustable FPR’s are not designed to hold pressure. People say they are built
    to bias free flow without regard for holding pressure after engine (fuel pump) is off.

    I guess my question is: is that actually so?

    If anyone else with an adjustable FPR, especially a Turbosmart, could let me know then that would be great.

    Also, I ran a small test with a hand pump where I tested the regulator’s ability to hold pressure. Basically, I attached the hand pump to the vacuum reference line. I did not add crimps or anything. I kept things simple. The regulator could withstand about five pounds of pressure but anything above that and the regulator lost pressure. Even when I pinched the line ends to ensure no air escaped from pressure, the pressure still dropped. Ergo, I think the FPR might be faulty.
     
  5. Oct 23, 2023 at 12:16 AM
    #5
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    As a second data point, I asked someone online who also uses a Turbosmart FPR if they lose pressure immediately after turning the ignition off. They said yes.
     
  6. Oct 23, 2023 at 12:38 AM
    #6
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    I uploaded a video of what is going on.

    I let the ignition sit at “run” for about thirty seconds before turning the engine over.
     
  7. Oct 23, 2023 at 9:01 AM
    #7
    Empty_Lord

    Empty_Lord Toyotaholic

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    Based off what I’ve seen with the mr2s, the FPR isn’t holding pressure

    my radium loses pressure. It’s just how it is
     
    Speedytech7[QUOTED] likes this.
  8. Oct 23, 2023 at 9:06 AM
    #8
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    Do our fuel pumps lack a check valve? If so, that might explain this. I think the adjustable FPR’s might not hold pressure by design, so without the OEM FPR to hold pressure - it relieves almost immediately.
     
  9. Oct 23, 2023 at 9:09 AM
    #9
    Empty_Lord

    Empty_Lord Toyotaholic

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    They have one. But it’s a return system. The factory FPR likely blocks bleed down from the return line

    the return line just dumps back into the tank
     
  10. Oct 23, 2023 at 9:10 AM
    #10
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    Interesting. I wonder if there’s anything I can do to avoid these long starts.
     
  11. Oct 23, 2023 at 9:11 AM
    #11
    Speedytech7

    Speedytech7 Toyota Cult Ombudsman

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    I know it is kind of down the road for you, but when you install a Haltech they prime on key on rather than cranking so it'll prime for you beforehand.
     
  12. Oct 23, 2023 at 9:15 AM
    #12
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    Hahaha, OK cool.

    I am sure someone has designed a switch with a diode to trick the fuel pump into turning on in the absence of aftermarket engine management system like Haltech. Tbh, I’m not sure how I feel about long starts every single time; probably hard on the starter.
     
  13. Oct 23, 2023 at 9:27 AM
    #13
    Empty_Lord

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    It won’t hurt it. How long of a start are we talking?
     
  14. Oct 23, 2023 at 9:35 AM
    #14
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    It depends. Sometimes, quite long. I haven't measured but maybe between 5 and 15 seconds. I can measure this morning.
     
  15. Oct 23, 2023 at 9:50 AM
    #15
    redneck_adjacent

    redneck_adjacent [OP] Well-Known Member

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    5 PSI supercharger 3" lift Bilstein 5100 shocks Old Man Emu springs General Spring leaf springs with 2" blocks and extended shackles 31" Firestone Destination XT tires LCE header and catback exhaust HPS CAI Tundra S13WE front brakes KC HiLites flood, ditch, fog, and backup lights Eaton Bussmann relay/fuse panel with custom power tray All Pro bumpers, sliders, and skid plates
    By the way, fellas, after giving this some thought, I realize that it should actually be quite easy to add a fuel pump switch, or switch the fuel pump from the ignition.

    I already have a fancy Eaton Bussmann installed in the engine bay with a ton of real estate for relays.
     

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