Table of Contents


  • ECM/ECU (Electronic control module/unit): This is the brain of the motorcycle; it makes calculations based on inputs coming from sensors mounted all over the engine.
  • WOT (Wide open throttle): The maximum opening of the throttle valve.
  • AFR (Air fuel ratio): The relationship of parts of fuel to the parts of air. 13.0(air) to 1(fuel) provides a richer burn and 14.6 - 14.7 is considered to be the 'ideal' air fuel ratio for fuel efficiency. Perfect efficiency calculations would require consistent atmospheric conditions, consistent temperatures, and a perfect atomization within the chamber. Often considered to be a stoichiometric calculations (see chemistry textbook), these values (~14.7 AFR) were determined to be ideal by lab testing in the automotive industry. Some discrepancy appears around the value itself: 14.6 or 14.7.
  • VE (Volumetric efficiency): Volumetric Efficiency is the efficiency at which the engine can move the charge into and out of the cylinders. This is arguably the most important value in calibrating an engines performance. The ECU uses the volumetric efficiency to determine how much fuel to add to the ignition chamber. The addition or subtraction of fuel is one of only two ECU adjustable variables that effects AFR correction. The objective in adjusting the VE is to calibrate the amount of fuel with the AFR Desired for that area or point of cylinder ignition. The O2 sensors will aid in these adjustments by giving measurements of the Actual AFR (Measured AFR). The Delphi Volumetric Efficiency number seen on VE tables is a value corresponding to the ratio of quantity of air that is trapped by the cylinder during induction over the swept volume of the cylinder under static conditions. There are several ways to improve volumetric efficiency, but a system wide approach must be used to fully realize potential.
  • MAP (Manifold absolute pressure): These sensors measure barometric absolute pressure in the intake manifold. By calculating the mass of the air going into the engine, air temperature, and the rotations per minute of the engine, the engine's ECU can determine the density of the air flowing into the fuel mixture. The ECU can then adjust air flow or fuel flow.
  • CKP or CP (Crank position sensor): This sensor tells the ECM when to fire and inject fuel depending on how fast the engine is running in revolutions per minute.
  • IAT (Intake air temperature): The ECM calculates how dense the air is from this input.
  • ET (Engine temperature): The ECM uses the signals from this sensor to determine if the engine is at operating temperature, or warming up.
  • Fuel Pressure Regulator: A mechanical device usually operated by vacuum form intake manifold that controls fuel pressure. It returns excess fuel from the fuel pump back to the fuel tank.
  • Fuel Injectors: The fuel injectors are electric valves that open and close to deliver fuel in spray form to the cylinder. They are controlled by the ECM to precisely deliver the correct amount of fuel at every engine speed, or RPM, and any given load. The time of injection is also known as the injector 'pulse width' and is measured in milliseconds. Injectors are rated by their flow rate such as in gm/sec, l/hr or grams per second.
  • Electric Fuel Pump or Fuel Pump: A 12-volt high-pressure fuel pump, usually located in the fuel tank, but it can be located outside as well. It supplies pressurized fuel to the fuel injectors.
  • IAC (Idle air control): An electric valve that's threaded to open and close as needed. This lets air into the engine for start-up, and idle operation when throttle valve is closed.
  • Closed Loop injection system: This circuit has 2 Oxygen sensors. The information on the difference of how much is coming out of the cylinder is relayed to the ECM and then adjusts the amount of fuel injected by shortening or lengthening the time the injectors are open.
  • O2 Oxygen sensor (sniffer): Tells the ECM how much oxygen is in the exhaust mixture so as to adjust to have the correct mixture.
  • RPM (Revolutions per minute): Used to measure engine speed.
  • TPS (Throttle position sensor): Displayed in percentages (0 to 100).