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Home > SUPPORT > Viper GEMS Controller

Viper GEMS Controller

Specific Setting and “Modes” are unique to MPI Viper Turbocharger Kits produced after June 2014. You can easily identify the current GEMS controller (which this document applies to) by the ABSENCE of a Boost Hose (typically blue) connecting to the GEMS module itself. The Current GEMS has an ELECTRONIC SENSOR install directly into the air box.  



Air/Fuel Gauges are not required for the MPI / Yamaha base turbo kit. This assumes that no adjustments are made to the Default SETTING that MPI ships in your GEMS Controller.

HOWEVER: If you are going to make adjustments to you MPI GEMS Controller it is strongly advised that you install a Wide Band higher quality gauge; MPI does make the Prologger® system, but any reputable gauge is fine. MPI supplies a M18-1.5mm weldment on the exhaust system to aid in sensor installation (the pipe will required drilling, but the weldment is already welded on).


Air/Fuel Ratios: The higher the number, the LEANER the sled is!

  • Idle: 12.0 to 14.5
    (Idle can be as lean as 14.7 on the gauge, although the Yamaha controller coupled with the MPI controller usually yields a richer reading (generally in the 12.5 range).

  • Engagement: 12.5 to 13.5
    (The engagement Air/Fuel ratio isn’t real critical, if it is in this area, it will just allow for nice easy cruising at engagement speed, making the sled easy to move around at slow speeds.

  • Midrange (0 to 1 lbs boost): 12.8 to 13.5
    (This is running at medium speeds, but the boost gauge still reading vacuum (assuming your boost gauge is properly connected the 5 way Blow-off valve manifold plumbing)  not boost pressure (it will show a negative number in the gauge or less than 1 pound of boost pressure).

  • Under boost: 11.3 to 11.8
    (This is anytime you are showing 1 or more pounds of boost or at wide open throttle or heavy load on the engine. Yamaha/MPI has this setting currently slightly richer than this, around 11.0 on the gauge, which is slightly safer, as that is the Yamaha/MPI recommendation. After some break-in miles we can alter this setting slightly if needed. We do not want to see any more than 12.0 on the gauge under boost!


Fuel Controller Settings & Modes (only applies to GEMS with external boost sensor mounted in AirBox):

It is clearly recommend that you do not initially change/adjust these modes, as it is easy to get confused on adjustments and adjust incorrectly.


*** You have to really pay attention when touching any of these buttons. Pushing the MODE button allows you to make changes. The modes are always Green, Yellow, Red, Green/Blue, Red/Blue in that exact order. Sometimes when you push the MODE button it will jump more than one color, so any adjustments require great attention to make sure you are adjusting in the correct MODE.***

  • A number blinking solid, means that is the number it is on. If two numbers are blinking (say both 2 & 3 are blinking) that means it is set on 2.5.

  • Mode 1: Idle (Green in color) The lower the number the leaner the idle mode.

  • Mode 2: Transition from Green to Green/Blue (Yellow in color). Generally needs no adjustment, has very little change.

  • Mode 3: Main Jet (Red in color) This is your wide open throttle setting. Lower number is leaner.

  • Mode 4: Boost/Fuel Adder (Green/Blue in color) This is how much fuel is added under boost pressure, use this first to adjust BOTH your wide open and your boost above 1 PSI air/fuel ratio.

  • Mode 5: Transition from Yellow (Mode 2) to Red (Mode 3) (Red/Blue in color). This is NOT a mixture setting (Mode 1,2,3 & 4 are all Mixture Settings). This is the adjustment that sets where your GEMS switches from cruising Mode to main jet Mode. The effect of this is a lower number is Richer when cruising! (this is backwards from the other 4 modes; Modes 1,2,3 & 4 a lower number is a Leaner setting).



After a GEMS unit has completed its startup procedure (scrolling lights for 7 seconds) it immediately enters the operational mode. In this mode the unit takes readings from all input wires to determine the current state of the vehicle. The inputs are used to determine which zone or zones should currently be active. If a zone is determined to be active then its output conditions are applied. Most output conditions are related to how much fuel should be added to the current injector signal resulting in more fuel. Remember it is possible to have more than one output condition being applied simultaneously. In the case where multiple fuel addition zones are active together (Boost Fuel and Load Based Fuel), the actual added fuel is found by combining the fuel amounts for each zone. If the combined fuel amount exceeds the set max additional fuel then the added fuel is lowered to the max additional fuel. Modes 1,2 & 3 (Green, Yellow & Red) are Load Fuel Modes. Blue Mode (LED #8) is Boost Fuel Mode and adds onto Mode 1,2 or 3.


The operational mode also involves updating the LED display to the current status. The LED display is engine duty cycle. The duty cycle is calculated and then the appropriate numbers of LEDs are turned on. The standard zone that is active determines the color of the LEDs.


Adjusting Modes

The Gen3 unit comes with three interactive buttons that are used to enter the adjusting mode and change the on-board tuning features’ light settings. When power is applied to the unit, the adjusting mode may be accessed at any time by pressing the Mode button. The adjusting mode is distinguishable by at least one or more LEDs flashing. The current adjust mode is determined by the color of the flashing LED(s) and whether or not the 8th LED is blinking blue. The adjusting mode is exited by waiting 7 seconds without pressing any buttons. Upon exiting, the light setting is automatically saved for each individual mode. If the vehicle dies or power is removed before the 7 seconds the settings are not saved.


After pressing the Mode button the 1st time the GEMS will enter the green mode adjustment. Either one or two connecting LEDs will begin blinking green. The positions are used to determine the current light setting for the corresponding adjust mode. There are 16 different light settings. The settings range from 0 to 8 in 0.5 increments. Holding the unit such that the LEDs are above the adjust buttons, settings 1 through 8 are recognized by the furthest left LED position as the whole number and if the LED to its immediate right is also blinking, add 0.5. Example: LEDs number 4 and 5 are both blinking together. Light setting is 4.5. A light setting of 0.5 and 1 are distinguishable by the rate at which the 1st LED is blinking. A faster blinking rate represents a light setting of 0.5. A light setting of 0 essentially means the adjust mode is not in use. Pressing the Mode button repeatedly enters each mode in order. When the last enabled mode is reached, pressing the Mode button again will bring the user back to the green mode, which is the first mode.


The adjusting display becomes visible when the user presses the mode button on the unit. The adjusting display consists of flashing LEDs. The adjusting display is not being viewed if an LED stays constant. The adjusting display serves as a visual reference as to what the current settings is for any on-board tuning adjustments. For each adjust mode the current light setting can be determined by the flashing LED position. Light settings of 1 and 0.5 are distinguishable by the rate at which the 1st LED is flashing. A light setting of 0.5 results in a faster blink rate.


The 8th LED Can will be turned on Blue for Boost above 1 psi. LEDs 1 through 7 are only available to display information about Modes 1,2 or 3 during unit operation. The 8th LED is setup to display when Boost above 1 psi is active. When Boost is present the 8th LED displays a constant blue. Take note that in some instances the LED may appear purple if the optional zone is active and the red zone is also active.


Thanks to Allan at Ulmer racing for hints and data.




Viper MTX Default Settings (Off-trail, typically above 6000ft):

Mode 1 - Green = 4.0

Mode 2 - Yellow = 4.5

Mode 3 - Red = 3.5

Mode 4 – Green/Blue = 6.5

Mode 5 – Red/Blue = 5.5


Viper Low-Elevation Default Settings (Trail, typically below 3000ft):

Mode 1 - Green = 4.0

Mode 2 - Yellow = 4.0

Mode 3 - Red = 3.0

Mode 4 – Green/Blue = 5.0

Mode 5 – Red/Blue = 3.5

Early Viper Trail Settings (recommend updating to Low-Elevation Settings above):

Mode 1 - Green = 4.0

Mode 2 - Yellow = 4.5

Mode 3 - Red = 3.5

Mode 4 – Green/Blue = 6.5

Mode 5 – Red/Blue = 2.5

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