How do you set igniton timing on a 93 Buick roadmaster?

Setting the ignition timing on a 1993 Buick Roadmaster (assuming it has the common LT1 engine) is not a simple procedure like on older carbureted vehicles. It's a computer-controlled system, and attempting to adjust the timing manually will likely damage the engine's computer or cause drivability issues. There's no distributor to adjust.

Instead of adjusting the timing directly, any timing-related issues should be addressed through diagnostics. Here's what you should do:

1. Diagnose the Problem: Before even thinking about timing, figure out *why* you think the timing is off. Are you experiencing poor performance, rough running, pinging (detonation), or a diagnostic trouble code (DTC)? This is crucial. Symptoms like these could be caused by many other things besides the ignition timing being off.

2. Check for Diagnostic Trouble Codes (DTCs): Use a scan tool (OBD-I scanner) to read the codes stored in the vehicle's computer. This will point to potential problems with sensors (like the crankshaft position sensor, camshaft position sensor, MAP sensor, etc.) that affect ignition timing.

3. Sensor Inspection and Replacement: If DTCs point to faulty sensors, replace them. Faulty sensors are the much more common cause of timing-related problems than actual timing being off on these systems.

4. Professional Diagnostics: If you can't identify the problem yourself using a scan tool, take the vehicle to a qualified mechanic with experience in OBD-I systems. They have the tools and expertise to diagnose and repair the issue correctly. Attempting to adjust the timing yourself, especially on a computer-controlled system, could result in significant damage.

In short: Don't try to adjust the ignition timing directly. Focus on proper diagnostics and sensor checks. The engine control module (ECM) manages the timing, and messing with it improperly can lead to serious consequences.