General Motors EST signal's
Here are some images that show the relationship between DistREF and EST.
Scope is triggered on the DREF Signal (A), timing is shown as the time between the falling edge of DREF and the rising edge of EST, this is the amount of timing commanded by the PCM. Coil turns on at the rising edge of EST sooner or later as timing advances or retards. Dwell time increases or decreases along with it. This image shows EST at 2000 RPM.
This image shows EST at idle speed with less advance and dwell.
This image shows EST and coil negative signal along the same time base, and is triggered off the EST signal. Coil on is the rising edge of the EST signal, coil off is the falling edge of the EST signal. Here you can see the on-off times of the EST signal in relation to the coil charging and firing in the primary signal. In the primary signal, coil on is the falling edge of the primary signal that lines up with the rising edge of the EST signal. Current limiting is the next event in the trace, then the coil turns off, (inductive kick) this lining up with the falling edge of EST signal.
This image shows the same relationship with the secondary signal.
More on EST coming soon...