* Engine speed (RPM): Timing advances at higher RPMs.
* Engine load: Timing changes depending on how hard the engine is working.
* Engine temperature: The ECM adjusts timing based on the engine's operating temperature.
* Sensor inputs: Various sensors (like the oxygen sensor and throttle position sensor) provide data the ECM uses to calculate optimal timing.
To find the *base* timing, you'd need a service manual specific to that year and model truck. Even then, the base timing is just a starting point for the ECM's adjustments. A timing light can be used to check the timing, but it will only show the *current* timing at a specific RPM and load, not the entire timing curve. A scan tool that can read the ECM data would be necessary to see the full timing map.
