Fixed Spark Mode - Checking Timing

To verify proper adjustment of spark timing, ECM will command a fixed 20° of spark advance and disable EGR operation whenever the following conditions are met:

1. Engine must be running and warm.
2. .9.5 must be displayed on ECC control head.
3. Engine speed must be under 900 RPM.
4. Transmission must be in park.

NOTE: The display of .9.5 may be displayed by either of the following methods:

a. Depress the ``instant/average'' button while .7.0 is displayed on the ECC control head. (If the display does not advance to Code .9.5, refer to Code .7.8 of the ``Switch Tests.'').
OR
b. Depress the ``instant/average'' button while parameter .1.3 of the engine data series is being displayed.

As long as above conditions are met and HEI system is working properly (codes 23 and 25 must not be set), a timing light can be used to verify that engine timing is adjusted correctly. If the engine is not at 20° +/- 2° BTDC under the above conditions, the base timing (10° BTDC) should be adjusted.

Refer to Computers and Control Systems / Testing Procedures for information on operating "On-Board Diagnostics".