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In the "good ol' days," before electronics, ignition timing was controlled by the relative rotation of the distributor to the camshaft. To advance the ignition timing you'd turn the distributor body slightly, and this would cause the points or electrical sensor to generate the spark slightly earlier. Likewise to retard the ignition timing.
Newer systems, such as your car, use electronics to determine when the spark occurs. Thus, rotating the distributor does nothing to alter ignition timing. A signal is taken from the engine rotation sensor, which is mounted on the rear of the block near the bellhousing. This sensor measures a TDC signal plus a series of pulses that tell the electronics how many degrees the engine has rotated. The electronics calculates exactly when the spark must occur and triggers the coil at the correct instant.
The picture below shows the flywheel of a basic '91 B230F engine. You can see the flywheel sensor at the top and the vaned ring around the circumference of the flywheel, near the ring gear.
In this case, the distributor does just (and only) what its name implies -- it distributes the spark pulse to the proper plug.
--
Don Foster (near Cape Cod, MA)
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