What you *should* do:
1. Check for codes: Use a scan tool (even a cheap OBD1 code reader will work) to read any trouble codes stored in the ECM. These codes will pinpoint potential problems that could be affecting the engine's performance and prevent you from accurately determining the timing.
2. Ensure proper operation: Verify that the following are functioning correctly:
* Throttle Position Sensor (TPS): A faulty TPS will throw off the engine's timing and fuel delivery.
* Crankshaft Position Sensor (CKP): Essential for the computer to know the engine's rotational position and control ignition timing.
* MAP sensor (Manifold Absolute Pressure): Affects fuel mixture and indirectly the timing.
* Coolant Temperature Sensor: Affects fuel mixture and ignition timing.
3. Data Logging (Ideal): If you have access to a more advanced scan tool that can data log, you could observe the actual ignition timing the ECM is commanding under various conditions. This provides the most accurate information.
4. Professional Diagnosis (Recommended): If you're not comfortable troubleshooting the electronic systems, take your truck to a qualified mechanic. They have the tools and knowledge to properly diagnose any issues and ensure the engine is running correctly. Trying to force a timing adjustment on a TBI system without understanding what the ECM is doing can lead to significant damage.
In short, there's no specific timing degree number you can set. The computer dynamically adjusts the ignition timing based on many factors. Focusing on the health of the sensors and the overall operation of the engine control system is paramount.
