I have a 96 Chevy k1500 with the vortec 350, no spark condition. I chased it down to the crank sensor, with the key off its getting a good ground from the vcm but when the ignition is on the voltage drop test shows it loosed it's ground and is actually energized to 8 volts! This is the purple wire pin b on the connector. I read somewhere that if you accidentally jump 12 v to that wire you will fry the computer so if it's putting out almost that it probably isn't a good sign. Any one familiar with 96-99 vortec vcm and crank sensor knowledge please chime in.

 

Disconnect the crank sensor and the VCM (I think it’s the blue connector but can’t recall exactly so unplug them all), then turn on the key and check again.

If the 8 volts is still present, it’s a harness short. If it’s gone, the VCM is to blame.

 

When I unplug the white plug the voltage drops and when I unplug the blue connector the voltage disappears. My theory was a bad system ground (12v+ short) but I checked and the system ground was good. My only thoughts are that it's either the vcm is energizing the wire do to it being faulty or the vcm is getting a 12 volts feed from a short somewhere in the wiring harness that is back feeding into the vcm causing me to get voltage when key is on.

 

Let’s try a different approach - this should be an easier way.

With the crank sensor and VCM disconnected, jumper the crank sensor ground circuit to battery positive.

Then, ground a test light at the battery, and work through each cavity of the VCM connectors - the test light should only illuminate on the sensor return circuit at the VCM connector.

If it lights at all on any other pins, there’s a short in the harness.

For additional assurance, since test lights won’t always light depending on the nature of the short, you can connect a meter in series to measure amperage draw or in parallel to measure voltage drop - a reading on any circuits other than the sensor return circuit indicates a harness short.

If the VCM is shorted internally and causing the 8 volts, repair services are available.