Fuel Injected Engines
The ECM will set timing at a specified value when the ALDL "test" terminal is grounded. See Fig 1. Note timing when terminal is not grounded. Increase engine speed to 2000 RPM. Ground "test" terminal and check for timing change. If timing changes, the EST is operating properly.
NOTE:
For information on specific ALDL connector locations, see appropriate component location chart in GM CCC article in the appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section. See list at end of article.