MULTI-PORT FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION SERVICE MANUAL NUMBER 23
Page 5B-30 90-861326--1 MARCH 1999
Base Ignition Timing
In order to check or change base timing on a HEI system the ECM has to be entered into
the service mode by using a scan tool or code tool. The IC module will go to base timing.
The ECM will stabilize timing to allow timing adjustment. The ECM incorporates a spark con-
trol override, which allows timing to be lowered if spark knock (detonation) is encountered
during normal operation. At this time, the timing can be adjusted by turning the distributor.
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Distributor Module Mode
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ECM Control Module
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