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Thread: need help adjusting jr fmu

  1. #1
    Inactive Member DC2NR's Avatar
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    ok when the car is at idle its suppose to sit 20-35 psi?

    so if i adjust the knob to add more fuel per pound of boost, how does it add it?

    whats the mathmatical ratio of it

    like

    chart
    Pounds-Fuel Pressure
    0-30
    1-40
    2-50
    3-60
    4-70
    5-80
    6-90

    something like that
    how do u dial the turn other then just hit and miss.

  2. #2
    Senior Hostboard Member JRCivic's Avatar
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    If you have stock sized injectors, then your idle pressure should be around 48 psi. If you remove the vaccuum line from the JR FMU while the engine is running, the pressure (static) should be 60 psi. If it is not, then you need to loosen the jam nut on the top of the JR FMU and adjust the static pressure.

    If you leave the vaccuum line connected to the JR FMU while you are adjusting the screw on top, you will NOT see any significant change in pressure because you are NOT adjusting the point in which you are viewing.

  3. #3
    Senior Hostboard Member JRCivic's Avatar
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    One more thing:

    You cannot adjust the rise rate of the JR FMU. You can only raise/lower the point in which it begins to rise from.

    Static pressure means NO vaccuum, NO boost... the internal diaphragm rests. When you connect the vaccuum line to the FMU, and the car is idling, the vaccuum suction lifts the diaphragm slightly inside the FMU and opens the orifice to the fuel return line more... thus, allowing more fuel to exit the fuel rail and flow toward the tank... and REDUCES pressure. This means that at wide open throttle under boost, the vaccuum line connected to the FMU sends boost pressure to the diaphragm and pushes it closer to the orifice to the fuel return... this reduces the amount of fuel that travels down the fuel return line toward the tank, and backs up fuel in the fuel rail. This INCREASES fuel pressure in the rail.

    Focus on the STATIC fuel pressure value... the rest falls into place automatically.

    <font color="#a62a2a" size="1">[ November 30, 2004 12:42 PM: Message edited by: JRCivic ]</font>

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    Inactive Member Tad3d's Avatar
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    hey interesting writeup,
    that was very informative, I feel like I understand better how the fmu works.

    oh and from what I've read/been told,
    the JR FMU is rated at 5:1, in that it raises the fuel pressure 5 parts(i assume psi?) per every pound of boost it sees.

    (correct me if i'm wrong).

  5. #5
    Inactive Member DC2NR's Avatar
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    thanks!

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    Senior Hostboard Member JRCivic's Avatar
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    Yes, the JR FMU is factory preset at approximately 5:1. This rise rate is NOT adjustable... it is controlled by the spring tension inside the unit.

  7. #7
    Inactive Member spidermancivic's Avatar
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    im glad someone ask this question, because, now, im back on the FMU. Two kids broke into my car 8 nights ago. stole my alpine stereo, broke my gauge pillar trying to rip out my gauges, and ran off with my conversion harness with me and my big brother chasing them. They obviously knew there was more in the car than just a stereo. I cant figure how they got in without breaking the window or lock.

    Anyways


    If you have stock sized injectors, then your idle pressure should be around 48 psi. If you remove the vaccuum line from the JR FMU while the engine is running, the pressure (static) should be 60 psi.
    <font size="2" face="Verdana, Helvetica, sans-serif">This is the same for a 99 b16 civic si@9 psi? When my engine is running at idle, the fuel pressure reads 70psi. When I remove the nipple from the FMU, the fuel pressure still reads 70 psi. When I rev the car with the nipple back on, the fuel pressure just twitches.

    Also, I am experiencing bogging issues. There is a CEL for the primary O2 sensor, which I can relate to the bogging. My useless autometer AF gauge is also in the red and just stays there. it also has no readings during the bog (so there is a relation, i figured closely to the o2 sensor).

    My question is, why would it just stay at 70 psi?

    <font color="#a62a2a"><font size="1">[ December 04, 2004 12:56 AM: Message edited by: spidermancivic ]</font></font>

    <font color="#a62a2a"><font size="1">[ December 04, 2004 01:02 AM: Message edited by: spidermancivic ]</font></font>


    PS: Just removed the spark plugs. They are dark brown with carbon deposits around them. The gap moved to .045. regapped them at .038

    <font color="#a62a2a" size="1">[ December 04, 2004 01:18 PM: Message edited by: spidermancivic ]</font>

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    Inactive Member spidermancivic's Avatar
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    there is also burnt dark brown residue around the spark plug electrodes. looks like fuel or oil.

  9. #9
    Inactive Member spidermancivic's Avatar
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    UPDATE

    swapped out the primary o2 sensor with a denso. car runs smoother now, no more studdering at lower rpms. still bogs at WOT.

  10. #10
    Inactive Member Y2KSI's Avatar
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    Isn't 70psi at static way to high? I run 8psi and my static is 43psi. I will have to check pulling off the line to the FMU to see what happens.

    Running that rich will definately kill your o2 sensor and cause CEL's like 41 or 61

    <font color="#a62a2a" size="1">[ December 10, 2004 03:53 PM: Message edited by: Y2KSI ]</font>

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