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Ignition Timing

NOTE: The ECM cannot read base timing. If base timing is incorrect, spark advance curve will be incorrect.
  1. Ensure engine is at normal operating temperature. With A/C off, operate engine at idle speed. Ensure SERVICE ENGINE SOON light is off. Ground Data Link Connector (DLC) diagnostic terminal. See Fig 1 .
  2. SERVICE ENGINE SOON light will flash while DLC is grounded. Connect inductive timing light to No. 1 spark plug wire. Notch in crankshaft pulley should align with stationary pointer on front of engine. See Fig 2 .
  3. Timing mark may fluctuate to each side of pointer, but should be centered on the pointer. Loosen distributor hold-down bolt and rotate distributor base to adjust (if necessary).
Fig 1: DLC Terminal ID
G121769Courtesy of GENERAL MOTORS CORP.
Fig 2: Locating Timing Marks-Up
G93C78081Courtesy of GENERAL MOTORS CORP.
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