injectors maxing out

Discussion in 'Fox 5.0 Mustang Tech' started by Beasly B, Sep 17, 2006.


  1. Beasly B

    Beasly B New Member

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    I'm having trouble with my 42lb injectors maxing out at high rpm and under boost, I have a 255 in the tank and a propump inline and a boost sensitive regulator, I have raised the fuel pressure to 58 with vac off and the injectors are still maxing out. It is a 302 shortblock and the rest is in my sig, Are my rails and lines too small or what's going on? I thought the stock rails could handle this type of setup?
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  2. joeyd0730

    joeyd0730 New Member

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    try adding a fmu it will bring your press up under boost and allow more fuel in during the cycle.
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  3. VG30DE

    VG30DE Founding Member

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    How much power are you making, you shouldnt be even close to max... I run stock lines, stock filter, one pump in tank, and stock rails and I'm just maxing out now...

    A FMU is a tuning band-aid that comes with the kit. Its not a permanent, nor a good solution.
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  4. Beasly B

    Beasly B New Member

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    Took a while to get a reply on this so I didn't check until now. I am supposed to be making around 500ish, hp, on my PMS screen at about 58k I max out to 100% but I don't go lean. I talked to Rick Anderson about this and he said it was okay as long as I didn't go lean. I am running about 58psi fuel pressure at max boost. I have all stock fuel rails and lines, a 255 intank and a propump inline. No fmu, don't want one.
    #4
  5. enyawix

    enyawix Member

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    Strange the chart on the MSD web site says you can make 500hp on 36lb injectors. What size are the injectors on the GT500?
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  6. LEE93COBRA

    LEE93COBRA New Member

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    42# injectors max out around 480-500 on blower cars. Upgrade to some 55-60 pounders and turn your fuel press back down to around 40 psi. You will be good to go after that
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  7. LordMustangGT

    LordMustangGT Member

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    I would say get begger injectors and bigger fuel rails!
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  8. VG30DE

    VG30DE Founding Member

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    ding ding ding we have a winner!

    The stock fuel lines cant support 42's never mind bigger. If you had a gauge you could watch during the pull, I bet you're losing at least 20 psi fuel pressure by the time you hit 5 grand. This is what happens when you have stock fuel lines/rails. They just get sucked dry:
    [​IMG]

    The injectors dont run out of flow, the flow to the injectors runs out. I started at 80 psi at idle, had 40 psi at 4 grand and only 25 psi by 5.5 grand (fuel pressure) with stock lines and rails.
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  9. LEE93COBRA

    LEE93COBRA New Member

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    I have to disagree. I have run both 42's and 60's with stock fuel rails with no problems whatsoever. If you lose 20 psi during a pull than there is something else wrong in the fuel system. If you lost a lot of fuel psi on your combo with 42's, it was due to a faulty pump.

    I could possibly see a fuel rail upgrade around 700rwhp and up but not any power level below that.

    Which brings me to another question. Why in the world would you have your psi at 80? That kills injectors having that much pressure on the back side of them.
    #9
  10. LEE93COBRA

    LEE93COBRA New Member

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    another thing..

    When I was blown and at the power level you reflect in your graph, I had 60# injectors, stock rails, stock lines, 255 intank and a KB BAP. At WOT my car would hit 50 psi of fuel and hold while maintaining low injector duty cycle.

    I actually had started out with 42's but they were not enough injector for 525-530rwhp
    #10
  11. aleborjas

    aleborjas New Member

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    check fuel pump, filter or put a in-line extra pump at least 67GPH!
    #11
  12. speedytang

    speedytang Founding Member

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    I make 535 rwhp with stock rails it sounds to me you have a weak FP or a voltage drop. Have you went with a 130a alternator yet to support the voltage drain.
    #12
  13. joeyd0730

    joeyd0730 New Member

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    by any chance are you running a c&l mass air meter?
    #13
  14. lvboost

    lvboost New Member

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    iImake 538 rearwheel with 36 pound injecters and i'm safe on the dyno also dont run the fmu
    #14
  15. millhouse

    millhouse Founding Member

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    You may be safe on the dyno but by no means is it recommended. Your likely pushing those injectors past 100% duty cycle and your fuel pressure has to be way high to compensate for your improper sized injectors.
    #15
  16. lvboost

    lvboost New Member

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    your right and i'm going to do a fuel system asap but this is going on mt 4th season with this set up "and i do kill my car"and it takes it like a champ
    #16

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