General Motors factory model, 4-Pin, HEI Module Notes by Lou Dudzik 6/10/15 update 6/10/15

These notes are specifically for old stock GM factory made 4-pin HEI module.  These are generally no longer available except as old stock or used parts. It is found on the 1977 Chevrolet Nova 5.7L V-8.

It behaves similarly to the Wells DR100 modules.  See the notes on the DR100 module for general operating notes.

These notes are only for the differences from the DR100 module.  Where information is still unknown, the values will be "x".  Assume the value from the DR100 notes.

The GM HEI module is not grounded through the heat sink, but is grounded through the mounting bolt which is electrically connected to the tab on the side.

With no input signal, and no current in the spark coil, the module uses x mA at x v. That's x watts.

C can stop an inductive spike of about x volts.  When the coil is "on", the voltage drop on C is about x volt.  

Terminal C will sink up to a maximum of about x amps.


Supply voltage: ~ 12v
Coil "on" when G > 1.30v
Coil "off" when G < 0.86v
At high RPM, W maxes out at about 6.5v

Supply voltage: ~ 14.5v
Coil "on" when G > 1.36v
Coil "off" when G < 0.86v
At high RPM, W maxes out at about 7.3v

W initial value is about 0.77 volts DC.

W is isolated from G with more than 100K ohms so signal mirroring is almost non-existant in this module.