Update - 10/10/2024

Owned by Austin Vann
Last updated: Oct 10, 2024
3 min read

MHD F/G App Update

MHD F/G App version 4.76 brings a small quality of life improvement for tuners. When NXM Port Injection is being used the Start of Injection tables now represent the Fuel Injection Window instead of Ignition Angle. This makes more sense for tuners as 720° - 0° injection window represents all fuel being injected for a single combustion event.

Tuners should adjust their existing Start of Injection tables to reflect these changes before having customers flash with the MHD F/G App version 4.76. Simply subtract 180* from your existing Start of Injection table values.

For this to make more sense we have created the diagrams below. When using direct injection it is common to support post-ignition injection. This can be used in specific operating conditions such as cat heating where raw fuel is injected into the cylinder at the end of the power stroke. In stock configuration the N54 supports injecting from 540° to -180° of ignition angle (in red below). For this reason our fuel injection window is offset by 180° (in green below). So an injection angle of 0° is actually -180°. This is fine for direct injection but presents problems when the engine is converted to port injection.

DI_Injection_Window.png

Leaving this 180° offset while using port injection presents a problem as 720° to 0° of injection would result in part of the fuel mass being used for one combustion event and the rest for the next combustion event due to the intake valve closing. For this reason we offset the fuel injection window (in green below) by -180° from the ignition angle (in red below). This adjustment means that 0° of fuel injection window represents when the intake valve has closed and fuel can no longer make it into the combustion chamber for that combustion cycle.

PI_Injection_Window.png

When NXM Port Injection is enabled we automatically apply this offset to the Start of Injection tables. So 720° in the Start of Injection table results in injection starting at 720° of engine position relative to the fuel injection window (in green above). This is much more intuitive for users and tuners.

XDF Update

The below tables have been added to XDF’s to provide more adjustability for tuners.

  • Enable LTFT - This will disable long term fuel trims temporarily while fueling is tuned.

  • Fuel Reactivation Adder - This table provides additional fuel mass on initial reactivation of fuel after fuel-cut off. Increasing these values will resolve situations where the engine wants to stumble or die when RPM decreases quickly such as a neutral rev.

  • Fuel Target Adder (Warmup) - This table is added to the AFR Target table Fuel (Main). This table allows negative values so it provides a nice method for allowing a richer AFR target during engine startup and warmup which is needed for port injection vehicles.

  • Fuel Target Adder (Cat Heating) - This table is identical to the one above but is used when cat heating is active. Modifying this table is important as in stock form this table will cause the AFR target to be too lean for port injection