Yamaha F150B Service Manual

Also see for F150B: Owner's manual Service manual Owner's manual

2-16Electronic control system012345678910AIdle speed controlEngine ECM controls the amount of intake air into the engine at idle by driving the ISC steppermotor based on the signals from each sensor to regulate the area of the passage bypassing themain pipe where the throttle valve is installed.Determination of the ISC valve openingBased on the signals from each sensor, engine ECM determines the extent to which the ISC valvemust be opened, and controls the ISC stepper motor operation to obtain the target ISC valve open-ing.ISC valveEngine ECM controls the amount of intake air at idle by driving the stepper motor, and changing thearea of the passage bypassing the main pipe where the throttle valve is installed. The stepper motormoves the ISC valve in 120 steps from fully open position to fully closed position. The ISC valveopens when the stepper motor is driven in reverse direction, and closes when the stepper motor isdriven in forward direction.A Intake air flowB Movement of ISC valvea ISC valveb Intake manifoldISC valve opening Engine conditionISC valve opening at engine start At engine start, ISC valve is opened relatively wider depending on theengine temperature. This increases the amount intake air andimproves the engine startability.ISC valve opening immediatelyafter engine startAfter engine start, the initial ISC valve opening determined by theengine temperature is reduced in steps and at constant interval untilthe idle speed is obtained.Dashpot ISC valve opening When the throttle lever is pulled back, ISC valve opening is controlledto prevent the engine speed from dropping off sharply.ISC valve opening with enginespeed compensationThe difference between the actual engine idle speed and the targetengine speed is calculated, and ISC valve opening is altered so thatthe target engine speed is obtained.#1#2#3#4ABab