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Once the engine warms up and goes into open loop, the duty cycle should fluctuate.
NOTE:
Refer to the car’s service manual to verify slope for each component.
Pulse Width Measurements
Pulse width is the length of time an actuator is energized. For example, fuel injectors are activated by an
electronic pulse from the Engine Control Module (ECM). This pulse generates a magnetic field that pulls the
injector nozzle valve open. The pulse ends and the injector nozzle closes. This Open-to-Close time is the pulse
width and is measured in milliseconds (mS).
Automotive applications for measuring pulse width include fuel, fuel mixture control solenoids and the idle air
control motor. The following example shows how to measure pulse width on port fuel injectors.
RPM IG
Black
Good
ground
Red
Jumper leads
from feedback
solenoid
Meter setup to measure pulse width:
•
Set the rotary switch to the RPM IG
(
RPM IG
) setting.
•
Press the “
%DUTY
” button until “
mS
” appears on the display.
•
Press and hold down the “
±TRIG
” button for 1 sec until the negative (-) trigger slope is displayed.
NOTE:
The On time for most fuel injectors is displayed on the negative (-) slope.
•
Insert the black lead in the “
COM
” jack.
•
Insert the red lead in the “
” jack.
