7.2 Fuel Settings 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
Here are what the settings do.
• Fuel Pump Mode - Specifies the following ways of controlling the fuel pump.
– On/Off: The fuel pump is switched on and off. Pressure is regulated mechanically. The MS3Pro can
monitor pressure and correct for it, but is not able to control the pressure directly.
– Open-Loop PWM: Used for pump speed control in combination with a regulator. The table on the right
hand side controls fuel pump duty as a function of RPM and fuel load.
– Closed loop PWM: The MS3Pro uses a fuel pressure sensor to target a specific pressure. Can be used
in an unregulated, returnless setup.
• Control interval - How often, in milliseconds, the MS3Pro updates its fuel pressure and temperature related
calculations.
• Fuel pump output - Allows changing the fuel pump output pin in PWM mode. If using another output pin
than the regular fuel pump output, the main fuel pump output pin will still operate in an on/off mode.
• Output frequency - The frequency used for PWM output.
• Output polarity - Normal polarity grounds the output to turn the fuel pump on and releases the output for
the off signal. Inverted reverses this.
• Fuel pressure regulation / correction - By preference, fuel systems use a vacuum/boost referenced reg-
ulator that maintains line pressure a fixed pressure above manifold pressure. Some GM fuel systems use a
fixed fuel pressure referenced to ambient air pressure instead. The vac referenced systems give even injec-
tor flow across all inlet pressure conditions and requires no compensation. The un-referenced systems give
a varying flow and require a calculation within the ECU to compensate. Enabling ’Fixed’ here turns on that
automatic compensation. Setting this to a custom curve allows you to use a user-adjustable compensation
curve based on a fuel pressure sensor.
• Static / Target Rail Differential Pressure - Allows you to specify the target fuel pressure in gauge pressure.
You can specify the pressure in both psi and kPa. Adjusting one will automatically adjust the other.
• Priming duty - When using PWM fuel pump control, specifies the duty cycle to use during the initial priming
pulse.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 164
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