Engine and Sequential Settings

This section contains the most basic settings required to run an engine with the MegaSquirt III.

Settings

• Required Fuel -
  

  Basic settings follow:

  • Engine Displacement - This should be the engine's displacement in Cubic Inches or Cubic Centimeters (depending on the CID vs. CC setting in the Units section).
  • Number of Cylinders - Enter the engine's number of cylinders. For the rotary engine, enter 4 cylinders for a 2-rotor engine, 6 cylinders for a 3-rotor engine, etc.
  • Injector Flow - Enter the amount of fuel that a single one of the engine's fuel injectors can flow in Pounds per Hour (lb/hr), or Cubic Centimeters per Minute (CC/min) (depending on the lb/hr or cc/min setting in the Units section).
  • Air-Fuel Ratio - Enter the air fuel ratio that should be targeted. Usually stoichiometric for the particular fuel in use should be used.

• Control Algorithm - This setting controls the method with which engine load is calculated. Engine load represents how hard the engine has to work and can be based on many factors such as manifold pressure, throttle position, air mass, or combinations of these. Note that this setting only sets the control algorithm for fuel injection and related settings; it does not set the control algorithm for ignition and related settings.

  The following settings may be selected:

  • Speed Density - Use the MAP (Manifold Absolute Pressure) sensor to determine load. In this case, the vertical axis of any fuel table lookups is in kilopascals (kPa). The maximum value reported by the MAP sensor (in non-turbo applications) will be the same as the barometric pressure.
  • Percent Baro - This setting is similar to the Speed Density setting in that the MAP sensor is used to determine load. However, instead of directly using the manifold pressure, the manifold pressure is divided by barometric pressure to give a percentage of barometric pressure. This setting can be useful for those who regularly drive at high altitudes. It ensures that regardless of barometric pressure, all table lookups operate over 0-100%.

    For example, if barometric pressure is 80 kPa, and the engine is operating at 50 kPa, the actual value used for table lookups is 50kPa/80kPa or 62.5%.

  • Alpha-N - Use the throttle position to determine load on the engine. Be sure to calibrate the throttle range using Tools->Calibrate TPS before using this setting.
  • MAFMAP - This setting is for users who are using a Mass Airflow sensor, but want to tune using the standard VE table. It calculates MAP based on the engine size, RPM, and other parameters. This calculated MAP is then used for fuel-based table lookups.
  • MAF - Use the MAF sensor and related calculations to directly determine the amount of fuel to inject. In this mode, the VE table is not used to determine the amount of fuel to inject. More information on this load mode is in another dialog's description.
  • ITB - This mode was created specifically for naturally aspirated engines running with independent throttle bodies. It combines alpha-n (at high engine loads) with speed density (at low engine loads), using the load calculation that makes the most sense at each RPM. For example, most ITB setups do not have good vacuum at idle or low RPM, and slightly touching the throttle makes them lose all vacuum, but at higher RPM start to respond more like a traditional single throttle body engine. This mode allows the use of speed density at low engine loads and switches to alpha-n at high loads, with an adjustable switchpoint curve over RPM (detailed in another section).
• Squirts Per Engine Cycle - Determines the number of times per engine cycle (two revolutions on a four-stroke engine) injectors are squirted when in a batch injection mode. This setting has no effect when injecting sequentially.
• Injector Staging - This setting is used only in batch injection modes. It determines whether the two injection channels are squirted at the same time, or in an alternating fashion.
• Engine Stroke - Sets the firmware for either a four-stroke engine or a two-stroke engine.
• Number of Cylinders - Sets the number of cylinders for the engine. Note that fully sequential injection is only possible with up to 8 cylinders.
• Injector Port Type - This setting is not used by the firmware and is included for historical purposes.
• Number of Injectors - Determine the number of injectors installed on the engine. Fully sequential injection is only possible with up to 8 cylinders and 8 injectors. When used with the staged injection feature, this should be set to the number of primary injectors.
• Engine Type - Determines whether the engine is an even-fire engine or odd-fire engine. An even fire engine is an engine where the crankshaft moves an equal number of degrees between each cylinder's top dead center (TDC). An odd fire engine may have a different number of degrees between TDC on some cylinders when compared with others.

Sequential Fuel Injection settings follow:

• Main fuel outputs -
  • Std fuel - Use the standard v3/3.57 board batch injector outputs.
  • MS3X fuel - Use the MS3X expansion board's outputs to drive the fuel injectors. Only one injector should be used per output.
• Sequential On -
  • Off - Use batch injection. On MS3x outputs, the channels are divided into two groups, and all injectors in a group are squirted simultaneously.
  • Semi-Sequential - Use batch injection, but allow the angle of injection to be specified. When used with the MS3X injector outputs, injectors should be wired in the same manner they would be wired for fully sequential injection.
  • Fully Sequential - Use fully sequential injection. In this mode, outputs A-H are squirted in sequence, so care must be taken to use the correct wiring for the engine's fireing order. For example, for a four cylinder engine with firing order 1-3-4-2, the following wiring should be used:
    • Output A - Cylinder 1
    • Output B - Cylinder 3
    • Output C - Cylinder 4
    • Output D - Cylinder 2
• Angle Specifies -
  • End of Squirt - The angle specified in the injector timing table specifies the angle of the end of each squirt. This should be used by most people for most engines.
  • Middle of Squirt - The angle specified in the injector timing table specifies the angle of the middle of each squirt.
  • Beginning of Squirt - The angle specified in the injector timing table specifies the angle of the beginning of each squirt.
• Injector Trim -
  • Off - Per-injector fuel trim is disabled. All injectors will have the same pulse-width.
  • On - Per-injector fuel trim is enabled. Each injector's pulse-width can be trimmed lower or higher than the value calculated using the fuel equation.

Firing order:

The firing order should be set to the firing order that your engine uses. It does not affect the order in which the outputs are triggered. Instead it is used to associate an injector trim table with a particular physical output so that when injector trim is applied, it is applied to the correct cylinder. It is also used if closed-loop EGO is being done per-cylinder.