How do you set the timing on a 1991 Cougar V6 3.8?

You can't "set" the timing on a 1991 Ford Cougar (or most other cars of that era) in the same way you would on older, points-based ignition systems. The 1991 Cougar 3.8L V6 uses a computer-controlled ignition system. The timing is controlled by the engine control module (ECM) and is adjusted automatically based on various sensor inputs (like engine temperature, throttle position, etc.). There's no distributor with a mechanical advance to adjust.

Trying to manually adjust the timing will likely damage the engine or the ECM. What you *can* do if you're experiencing timing-related issues (like poor performance, misfires, or rough running) is:

* Check for diagnostic trouble codes (DTCs): Your Cougar likely has a way to retrieve diagnostic trouble codes. This will help pinpoint the source of the problem. The method for retrieving these codes varies depending on the specific model year and options, but often involves connecting a code reader or bridging certain connectors under the dashboard.

* Inspect the ignition system components: Check the ignition coil, spark plug wires, and spark plugs for wear, damage, or cracks. Replace any faulty components.

* Check the various sensors: Faulty sensors (like the crankshaft position sensor, camshaft position sensor, or MAP sensor) can cause the ECM to miscalculate the timing. Inspect these sensors for damage or corrosion and replace as needed. A professional mechanic will have the tools to test these sensors properly.

* Have a professional diagnose the problem: If you've checked the obvious components and still have issues, taking your Cougar to a qualified mechanic is the best course of action. They have the tools and expertise to diagnose and fix problems with the ECM, sensors, and other sophisticated parts of the engine's control system.

In short, forget about adjusting timing manually. Focus on diagnosing the underlying problem using the methods above.