Quote:
Originally Posted by some_other_dave
Probably because the ECU does not actually know when the ignition timing is. It simply advances or retards it from the current static timing.
-soD
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Inside the distributor, there are a few extra wires that detect and regulate the spark. It's traditionally connected to the spark pack or ignition source with a feedback wire to the ECU. The "timing" can be interrupted electronically from the ECU vs. the physical point of electrification as the distrib spins and connects with the points. This produces the "timing range".
Which is why you should tune ECU-independent. After that, the range of advance/retard is limited electronically.
RH77