Fuel Rail PSI under boost

Discussion in '2005+ Mustang GT 4.6L Tech' started by golkhl, May 20, 2019.

  1. golkhl

    golkhl forum member

    965
    18
    Quick question for you guys with supercharged 4.6 3v, what is your fuel rail psi under boost? At idle and normal driving, my gauge is reading right around 40 psi, under boost it spikes up to at least 67 psi.
    I am trying to trouble shoot a slight hesitation/bogging condition I am getting from time to time. I have cleaned the maf and throttle body, cleaned the air filter, installed new plugs, fuel filter was changed last year.
    Fuel pump is stock with 60k miles, thinking the filter sock might need to be cleaned or replaced.
    Currently running an off-road x, and upstream O2’s have been replaced in the last 5 years, and car is throwing no codes.
     
  2. golkhl

    golkhl forum member

    965
    18
    FPDC is 16psi at idle, and 41psi at 5psi of boost.
     
  3. 05stroker

    05stroker Never enough power guy!

    13,005
    43
    If I'm not mistaken on a returnless system the tuner sets what he wants a fuel pressure to be at wide open throttle under boost. If that's wrong somebody please correct me
     
  4. 01yellerCobra

    01yellerCobra forum member

    1,973
    77
    How are you watching the pressure? It should go up under boost. It has to over come the boost pressure on the bottom of the injector. So if base setting is 40psi it's making 20psi of boost fuel pressure needs to go up to 60psi to make it out of the injector. It's also why pressure drops at idle. There's a vacuum under the injector so it doesn't need as much pressure.

    FPDC works in percentage. Not psi. I would watch FPDC and pressure drop across the injectors.
     
    hammeron likes this.
  5. golkhl

    golkhl forum member

    965
    18
    I am watching the Fuel rail pressure and Fpdc on my aeroforce gauge. My bad on stating psi for the fpdc, from what I understand the gauge reads 1/2 of the actual percentage. Under boost, gauge is reading 41, which should mean that I am using 82% of the fuel systems max output.
    Trying to troubleshoot a slight hestitation/bogging condition that happens at around 3500 rpm.
     
  6. 01yellerCobra

    01yellerCobra forum member

    1,973
    77
    Has it always had the hesitation or is it a recent development? Is it only at part throttle?
     
  7. golkhl

    golkhl forum member

    965
    18
    Would happen from time to time in the past, when it did, I would clean the maf and throttle body, and it would go away. I just cleaned the maf/throttle body/ air filter, installed new NGK 7554’s gapped to .035”, and now the hesitation/bogging is worse than before. Does not happen all the time, but when it does, it seems to be around 3k-3.5k rpm. Car is throwing no codes, going to put a new fuel filter in, and than might have to pull the fuel pump and check the filter sock.
     
  8. JeremyH

    JeremyH 3V Fuel Guru S197 Team Member

    20,658
    94
    What year car there is a hesitation tsb for 05-06.

    Generally pressure will be around 30psi at idle and some number above 40 at wot in boost depending on your boost level.

    Your running a stock pump still?
     
  9. Vallee

    Vallee forum member

    117
    35
    After installing my supercharger with the GT500 fuel system mine had that annoyingly stumble and hesitation, I usally noticed it when cruising and then hammering down... It did this on both of my engine builds, turned out to be tune related... Lito corrected it. My fuel pressure spikes near 70 PSI under high boost...

     
    06monera96 likes this.
  10. golkhl

    golkhl forum member

    965
    18
    Car is an 08, stock fuel pump with 60k miles, running a KB boost a pump, and the S&H wire upgrade. Car was locally dyno tuned a few years back.
     
  11. golkhl

    golkhl forum member

    965
    18
    Jeremy: do you still sell the upgraded drop in fuel pump assembly?
     
  12. Pentalab

    Pentalab forum member

    2,696
    123
    I have a constant 40 psi at idle....and also at 6+ krpm.... fuel pressure does not change. Read on my aeroforce gauges.

    FPDC at idle is 40% (20 on the aeroforce gauges).... and is 80% (40 on aeroforce gauges) at 6+ krpm

    10 gauge wire upgrade has been done, and the above data is after the 10 gauge wire upgrade.

    OEM fuel pump used. NO Bap used.

    M90 blower used on my 2010 Auto. OEM pulley. 5.8 psi boost.
     
  13. 01yellerCobra

    01yellerCobra forum member

    1,973
    77
    You're probably watching Pressure Drop Across the Injectors. Which is supposed to stay around 40psi all the time.
     
  14. 06monera96

    06monera96 LeShawno

    333
    8
    heheheh, Me and Lito actually worked this.

    When I would be in Mexico and i go to shift hard like power shift I would lose pressure bog and then pick up
    With a little data logging and some modding by lito, we got that fixed up.

    Highly impressed by Lito when we found a fix for this issue with my M90,
    Basically, when you let off the fuel pump, spike the fuel to 60-70 psi to get the fuel rail ready for a Power Slam! lol (My own theory of what mods he did to my tune)