Oscilloscope Patterns and Waveforms

Fuel Injector:

Explanation of Wave Pattern

Normally the power voltage is displayed, but when an injector drive "ON" signal is output by the engine control module. voltage drops to around OV for the duration of this "ON" signal only. When the drive signal from the engine control module becomes "OFF". a voltage peak appears due to the coil back electromotive force. and after this, it returns to power voltage.

Injector drive time: The fuel injection time computed by the engine control module from the output values from each sensor such as the volume air flow sensor Injector drive time = effective injection time + ineffective injection time

(Ineffective injection time:compensates for retarded injector operation due to the drop in power source voltage.) Solenoid back electromotive force: When the injector drive signal from the engine control module is turned OFF, a back electromagnetic force is generated in the injector coil (Approx. 65-75V).

Power source voltage: When there is no "ON" signal from the engine control module, power supply voltage is displayed. When this power supply voltage is low, the ineffective injection time is long and injector drive time also is long.