Power Probe IV
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ECM V
= ECM Ground Voltage - The engine computer activates each fuel injector by com-
pleting the ground circuit with an internal transistor switch. When the fuel injector is energized, the
ECM ground voltage should be close to zero volts. Actual measured ECM ground voltage can vary,
and may be closer to 0.5 volts because of the internal resistance of the switching transistor.
Advanced Testing Operations
Fuel Injector Mode
ON- ms
= Injector Pulse On-Time (milliseconds) - This is the total amount of time that the fuel
injector is energized and supplying fuel to the cylinder. This can be compared to scan tool PID data
to see if commanded on-time equals actual on-time
IND-K V
= Inductive Kick Voltage - Normal inductive kicks range between 55 and 90 volts.
You should see a similar voltage number from each of injectors on the engine. Note: The height of
the inductive kick is sometimes cut-off by an internal ECM diode to about 35 to 45 volts. Note: This
test does not apply to hi-pressure injectors used on diesel engines and gasoline direct-injection en-
gines.
INJ V
= Injector Supply Voltage - This is the battery power being supplied through the fuel
injector itself. Measured voltage should be close to full battery voltage. There may be small volt-
age drops in the circuit, however, anything more than 0.5 volt loss from the source battery voltage
should be investigated.
• Select FUEL INJ from the Power Probe IV’s test
menu.
1
2
3
4
4
3
2
1
• The main screen will display complete injector circuit
data for quick comprehensive injector circuit diag-
noses.
• These four data points represent the corresponding
waveform points. (see pg. 15)
• When the engine is running (or cranking) the Power
Probe IV’s red and green indicator LEDs will blink to
indicate a good signal from the ECM/PCM.
Page 17
• Back-probe on the negative side of the injector,
either at the injector or at the PCM.
