5 terminal HEI module

[john spears]

dzorde asks about the function of the 5 terminal HEI module. This was an
early control system for knock control only. The distributor (dizzy?) still
had centrifugal weights and a vacuum advance.  The positive line of the two
wire pickup coil is sent to an ESC controller, instead of going right to the
HEI module as in the 4 terminal variety. If the ESC controller is not
detecting any knock input it simply allows the pickup coil signal to return
to the module and fire the coil. If it does detect knock, it DELAYS the
return of the pickup coil signal for a time equal to the numbers of degrees
of retard it commands, based on a lookup table in the ESC controller. The
5th terminal is simply used as the line to return the pickup coil signal on.
It was an early, rather crude method of knock retard, but was perceived as a
great accomplishment at the time. I make this assumption based on the size
of the "ESC" emblem they used to put on the tailgate of trucks equipped with
this system. When I am doing a repair on these systems, most customers allow
me to just loop the positive pickup coil wire back into the module and throw
the ESC controller away!

                John Spears 
Speartech Fuel Injection Systems