Distributor Operation

Water Pump Removal:

Ignition Coil And Distributor Location:

Distributor:

DESCRIPTION
The distributor is mounted behind the water pump and is driven directly by the camshaft. In addition to directing the sparking voltage to the correct spark plug wire, the distributor provides the ECM with two reference signals that the ECM uses for calculating ignition timing. A high resolution signal and a low resolution signal.

OPERATION
Other than thte rotor, inside the distributor is a signal disc and two optical sensors. One optical sensor (the high resolution sensor) "reads" a row of 360 equally spaced slots in the signal disc. The other sensor (low resolution sensor) "reads" a row of 8 slots of different widths. The signals from the optical sensors are amplified and used to operate two transistor drivers that alternately ground and open the 5 volt reference circuits from the ECM, producing the timing control signals that the ECM "reads". Timing signals toggle between 0 and 5 volts as the camshaft turns. From these signals, the ECM calculates ignition timing and can determine which cylinder is about to be fired, for cylinder selective electronic spark timing control.

Both of thes signals must be present for the engine to start, however, if the high relosution signal is lost while the engine is running, the engine will continue running, but performance will be reduced.

Once the ECM calculates the ignition timing, a timing signal is sent to the ignition module, on the EST circuit, triggering the ignition coil. The EST signal alternates between a "low" state (approx. 0.5 volt), and a "high" state (approx. 4.5 volts.) When the EST signal is "High", the ignition module completes the ignition coil primary circuit to ground and current flows. When the EST signal goes "Low", the module opens the coil primary circuit, primary current flow through the coil is interrupted and the coil "fires".