Attempting to adjust the timing directly will likely damage the engine or the computer. The timing is adjusted by the computer itself, and any intervention should be done through diagnostics and potentially replacing faulty components.
If you're having problems with the timing (rough running, poor fuel economy, etc.), here's the proper approach:
1. Diagnose the problem: Don't jump to conclusions. Use an OBD1 scanner (for a 1987 truck) to read the trouble codes. These codes will point you to the likely culprit. Common issues that *might* manifest as bad timing include:
* Faulty crankshaft position sensor (CKP): This sensor tells the computer where the crankshaft is, crucial for precise timing.
* Faulty camshaft position sensor (CMP): Similar to the CKP, but for the camshaft.
* Faulty MAP sensor (Manifold Absolute Pressure): This sensor tells the computer about engine load, which affects timing.
* Faulty oxygen sensor(s): Affects fuel mixture, indirectly influencing timing.
* Vacuum leaks: Can disrupt the sensors' readings and lead to erratic timing.
* Ignition coil or wires: Faulty ignition components can cause misfires, which the computer may try to compensate for, leading to seemingly incorrect timing.
2. Repair the identified fault: Once you have the trouble codes, you can address the specific problem. This might involve replacing a sensor, fixing a vacuum leak, or repairing a faulty ignition component.
3. Data Logging (Advanced): If you have advanced diagnostic equipment, you might be able to data log the timing advance to see if it's within the acceptable range. This requires specialized knowledge and tools.
In short: Don't try to adjust the timing yourself. Use diagnostic tools to identify and repair the underlying problem. Taking it to a mechanic familiar with older GM vehicles and OBD1 systems is often the most efficient and reliable solution. They'll have the right equipment and knowledge to properly diagnose and fix the issue.
