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Whats everyone running fuel pressure wise?

Posted by Re4peR26, Feb 3, 2008

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  1. Re4peR26

    Re4peR26 Proven Member

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    Ravenna, Ohio
    Well in my car i have been running 42.5 psi at idle and about 70psi at 18lbs of boost. Werid thing is thats the only way my car likes to run.... so i just want to see what some of you guys are running as far as Fuel/Boost
     
  2. snowborder714

    snowborder714 Moderator

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    Mechanicsburg, Pennsylvania
    How are you seeing more than a 1:1 ratio between fuel and boost? What AFPR are you using?
     

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    1995 Mitsubishi Eclipse GST
    12.529 @ 110.820 · 2G DSM
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  3. GVR4592

    GVR4592 Proven Member

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    I believe 1g fuel pressure is supposed to be 36.3 with the vacuum line disconnected. Having high fuel pressure without compensating for it with some sort of tuning device, is going to cause problems.
     
    GVR4592

    611  0

    1992 Mitsubishi Galant VR-4
    manual · Galant VR-4
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  4. Re4peR26

    Re4peR26 Proven Member

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    Im using the aero one. And as far as problems go this is the best my car has ever ran. thats being completly honest. She doesnt want to run when the fuel pressure is that low.. stumbles on her face and if i blip the throttle it wont rev it will bog when its that low, Now all she does it want to go without any hesitation.
     
  5. snowborder714

    snowborder714 Moderator

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    Mechanicsburg, Pennsylvania
    Your fuel pressure should be:

    Have you checked for boost leaks lately? Did you put teflon tape on your AFPR fittings (the NPT ones, not the AN ones)?
     

    3K  0

    1995 Mitsubishi Eclipse GST
    12.529 @ 110.820 · 2G DSM
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  6. Re4peR26

    Re4peR26 Proven Member

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    Ravenna, Ohio
    Yes, I had 3 boost leaks fixed them all. And yes i used teflon tape on the fittings. Casue i have the liquid filled gauge under the hood and the electric on in the car.
     
  7. Spades

    Spades Proven Member

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    Beaumont, California


    Looks like you are testing it with the vacuum hose still connected @ idle which would explain your ratio being greater than 1:1 with boost. Proper way to test is with the hose disconnected as stated above. Judging from your #s, it looks like your base fuel pressure is at 52psi @ idle with the vac hose disconnected.... thats too high.
     

    596  0

    1997 Eagle Talon TSi
    · 2G DSM
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  8. Re4peR26

    Re4peR26 Proven Member

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    Negative. My base psi at idle is 42 with it connected.
     
  9. steve

    steve DSM Wiseman

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    It would look that way. Calculating from provided boost and from a guess at vacuum.
    Assuming the gauges are accurate.

    Fuel Pressure (psi) = Base Pressure (psi) + Reference Pressure (psi)

    70 = x + 17
    70 - 17 = x
    53 = x

    42.5 = x + (-19 in hg)
    42.5 = x + (-9.3 psi)
    42.5 + 9.3 = x
    51.8 = x

    Now is this bad?

    It's different than the factory base pressure but as long as the car is retuned for the change in effective flow rate of the injectors it's not "bad". On a stock ECU without tuning, it would be seriously rich and imply something else is wrong if it ran well.

    70 psi at the rail may be a problem. As you move back to the fuel pump there are restrictions (losses) that add to the actual pressure seen at the pump. The pump its self has a pressure relief valve that will begin to vent fuel once exceeded reducing the pump flow. These are typically around 70-80 psi except for the "HP" pumps.
     

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    1991 Mitsubishi Eclipse GSX
    manual · 1G DSM
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  10. 90laserRSfwd

    90laserRSfwd Proven Member

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    what is the base fuel pressure at with the vac. line DISCONNECTED ?
     

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    1992 Plymouth Laser RS Turbo
    manual · 1G DSM
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  11. Re4peR26

    Re4peR26 Proven Member

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    Very true.... Your a real smart guy i give you props on that.. here would be a good question if i was running to rich i would have some black smoke or black plugs.. Well this is not the case for me. No smoke and plugs look good. and a correction to what i stated above.. At 16-18psi its running 63 psi
     
  12. Re4peR26

    Re4peR26 Proven Member

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    well im going out to work on it now.. So ill let you guys no here inna tid bit
     
  13. Spades

    Spades Proven Member

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    Yes, but base pressure is measured when it is DISCONNECTED. Thats why I said that you will be right around 52 psi when you disconnect it.
     

    596  0

    1997 Eagle Talon TSi
    · 2G DSM
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  14. Re4peR26

    Re4peR26 Proven Member

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    Update: i set the base psi to right around 38 closest i could get it, Then connected it took it for a drive... Well under boost or hard accelation it was decent... but light throttle no way boggs all to hell.. So went back home upped it to 40psi base then it was a little better still bogs a little bit more. So im just going to put it back to 43 base psi.. seems as if thats all it gets along with.
     
  15. kenamond

    kenamond DSM Wiseman

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    Los Alamos, New Mexico
    Is your car an automatic? I don't know enough about 1g awd options (like maybe awd/gsx didn't have an auto option on 1gs). If yours is an auto and from what was mentioned already in the thread, 43psi base fuel pressure might be correct.
     

    943  0

    1997 Eagle Talon TSi AWD
    manual · 2G DSM
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  16. goldenTSI

    goldenTSI Probationary Member

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    Colorado Springs, Colorado
    What kind of FPR's are other people using? Has anybody used an MSD2222 fpr on there car? I have one that I used on my starion and I am going to make a fuel return fitting for the rail so that I can use this regulator and not have to worry about all tha AN fittings. I am eager to see if this makes as much of a difference as it did on my Starion.

    And I should shoot for about 36psi on a 1g manual by the info above right!
     
  17. kenamond

    kenamond DSM Wiseman

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    You could do this, but the stock FPR will do just fine until you start pushing the stock fuel system. I'd recommend spending your money on parts in the order you need them. But I have no idea if that FPR would work or not. As long as it rises at 1:1, is adjustable, can flow more than the stock FPR without overrun, and can be installed, why not? Most folks around here use an Aeromotive AFPR.
     

    943  0

    1997 Eagle Talon TSi AWD
    manual · 2G DSM
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  18. goldenTSI

    goldenTSI Probationary Member

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    Well when I plan I using this I hope to be running a walbro 255 soon, but I never really hear about anybody using the MSD2222 on thier DSM it does have all the features you mentioned. Thanks for the feedback.
     
  19. Re4peR26

    Re4peR26 Proven Member

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    my car is 5 spd.. is it really neccasry the run at the stock psi i have fuel system upgrades 16g turbo all of the supporting mods. I did another boost leak test found another one.. fixed it. didnt help any.
     
  20. goldenTSI

    goldenTSI Probationary Member

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    Sorry I wasnt trying to hijack your thread....have you checked your plugs and wire to make sure that they are gapped good and the wires suppling good spark. The raised fuel preasure may fix your hesitation but I dont think its the cause for it.
     
  21. kenamond

    kenamond DSM Wiseman

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    Los Alamos, New Mexico
    Base fuel pressure *should* be independent of the turbo and FP you have as long as you're within the capabilities of your injectors.

    Think about it like this: The injector is just an on/off valve. The ECU says "open" then quickly says "close". The ECU knows that you have 450cc/min injectors and knows that you have 38psi-ish fuel pressure. Therefore, it knows that a specific amount of fuel will be delivered when it opens the injector for a specific duration (called the pulse width).

    The fuel pump just has to provide *enough* fuel to keep the fuel pressure high enough. The FPR is the part of the system that is responsible for keeping the pressure "just right". As long as the fuel pump is cranking out vast quantities of fuel and as long as the AFPR is capable of letting enough of this recycle back to the gas tank, the fuel pump doesn't matter.

    It's all about keeping the pressure difference on each end of the injector right at 38psi. Keep in mind that the two ends of the injector are the fuel rail and the intake ports. The intake ports, however are boosted (connect right to the intake manifold). So when you're running 10psi boost, the FPR has to keep the fuel rail pressure at 38+10=48psi pressure. Every increase of 1psi boost requires a corresponding 1psi increase in fuel rail pressure by the AFPR. That's all the 1:1 stuff folks talk about with an FPR. Also, when idling, you might have -10psi in the intake manifold. The FPR then has to keep the fuel rail pressure at 38-10psi=28psi pressure. That's why there's a vaccuum line on the AFPR from the intake manifold (lets it know the IM pressure). But wherever your IM pressure is at (vaccuum or boost), the FPR is keeping the *difference* in pressure across the injectors right at 38psi, and this 38psi is the "base fuel pressure".

    With a fixed pressure differential across the injectors, and with a specific injector, the ECU knows how long it has to open the injectors to deliver the correct mass of fuel to each cylinder. The ECU has been hard-wired based on a factory tune that works for those injectors and base fuel pressure.

    So I don't know why you need to set your fuel pressure higher. If the injectors are flowing normally, then you'd think that a higher base fuel pressure would cause you to run rich (higher pressure difference will force more fuel in a given pulse width than a lower base fuel pressure).

    Maybe your injectors are clogged or sticking. I really don't know why this works for you.
     

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    1997 Eagle Talon TSi AWD
    manual · 2G DSM
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  22. Re4peR26

    Re4peR26 Proven Member

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    Ravenna, Ohio
    I have no idea either its really werid.. It only likes the 43psi base i would love to find out why.. Im going to invest in injectors soon. somewhere between 6-800-cc include the odd numbers but you know what i mean. Im getting DSM link soon. and next fall complete rebuild BR stage 1 bottom end on BR stage 3 head So im just getting my bolt ons ready for the motor.
     
  23. Kyromoto

    Kyromoto Proven Member

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    Fontana, California
    I hear everyone talking about a DSMlink. I have no idea what this is and im about to do some reading on it but what is its purpose and is it somthing important I should get? thanks and sorry for the noob question
     
  24. Kyromoto

    Kyromoto Proven Member

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    ok now i know what it is... now the question is do i need 1? And if i got 1 how hard is it to figure out how to "tune" your car. What can the DSMlink adjust? sorry again for the questions
     
  25. thekellbeast

    thekellbeast Proven Member

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    Portland, Maine
    Stock base pressure plus 1:1 rising rate with boost.
     

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