This vehicle utilizes a computer compensating system to adjust ignition timing. Ignition timing is completely adjusted by the computer. Meaning, as you rotate the distributor... the computer is adjusting the ignition timing to what it thinks it should be. Setting timing on this vehicle with a timing light is not an option. You must use a scantool to set the timing, or what GM calls Camshaft Retard.
Camshaft Retard is set as follows using a scantool.
TEST PROCEDURE You cannot adjust the ignition timing as I just explained. You may need to adjust the distributor in order to prevent crossfire. To insure proper alignment of the distributor, perform the following:With the ignition OFF, connect the scan tool. Start the engine. Allow the engine to idle until the engine reaches the normal operating temperature.IMPORTANT: The Cam Retard Offset reading will not be accurate below 1,000 RPM .Increase the engine speed to 1,000 RPM while performing the following steps. Use the scan tool in order to monitor the Cam Retard Offset in the Datastream option. If the Cam Retard indicates a value of 0 degrees , the distributor is properly adjusted. If the Cam Retard does not indicate 0 degrees , the distributor must be adjusted.ADJUSTMENT PROCEDURE
With the engine OFF, slightly loosen the distributor hold down bolt.IMPORTANT: The Cam Retard Offset reading will not be accurate below 1,000 RPM .Start the engine and raise the engine speed to 1,000 RPM . Use the scan tool in order to monitor the Cam Retard Offset.
Rotate the distributor as follows:
To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
To compensate for a positive reading, rotate the distributor in the clockwise direction.Repeat step 4 until 0 degrees is obtained.
Turn OFF the ignition.Tighten the distributor hold-down bolt.Tighten Tighten the bolt to 3 N.m (25 lb ft) .Start the engine. Raise the engine speed to 1,000 RPM and view the Camshaft Retard Offset.
It's the ONLY way. Good luck.
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