Here's a breakdown of troubleshooting steps:
1. Heat Soak Issues:
* Ignition Module/Coil: The most likely suspect is the ignition module or coil overheating after the engine warms up slightly. These components are prone to failure, especially in older vehicles. After running for a minute, they get hot enough to malfunction. Check for any obvious signs of damage (cracks, burns). Consider replacing the ignition module and coil as a set, as they often fail together.
* Distributor: While less common, the distributor cap, rotor, or pickup coil within the distributor could also be causing intermittent issues exacerbated by heat. Inspect for cracks, arcing, or wear on the cap and rotor. The pickup coil is harder to diagnose without specialized tools.
* Worn-out wires: Heat can make already-frayed or poorly-connected wires more problematic. Inspect all high-voltage ignition wires (from the coil to the distributor cap and from the cap to the spark plugs) for damage or cracks. Replace if necessary.
2. Other Possibilities:
* Coolant Temperature Sensor (CTS): A faulty CTS can provide incorrect readings to the engine control unit (ECU), leading to poor fuel mixture and rough running, especially as the engine warms up.
3. Troubleshooting Steps:
1. Visual Inspection: Thoroughly inspect all ignition components (wires, coil, module, distributor cap, rotor) for any signs of damage.
2. Check for Spark: Use a spark tester to verify that you have a strong, consistent spark at the spark plugs after the engine stalls.
3. Check for Fuel Delivery: While fuel pressure is okay at 40 psi, temporarily disconnect the fuel line at the fuel rail (with the engine OFF, of course) and crank the engine to check if fuel is flowing. It should be a steady, strong stream.
4. Monitor Engine Temperature: Pay close attention to the engine temperature gauge. If it rises quickly, there could be a cooling system problem that is indirectly causing the issue.
5. Test the Coolant Temperature Sensor (CTS): You can test this sensor with a multimeter, but you'll need a service manual for the specific engine to determine the correct resistance readings at various temperatures.
Important Notes:
* Safety First: Always disconnect the negative battery terminal before working on any electrical components.
* Service Manual: Obtaining a service manual for the 1986 V6 engine will be extremely helpful. It provides wiring diagrams, specifications, and troubleshooting guides.
* Professional Help: If you are not comfortable working on the vehicle's electrical system, take it to a qualified mechanic.
Start with the ignition system inspection and testing, as that's the most likely cause given the symptoms. If that doesn't solve the problem, move on to the other possibilities. Remember to check for any obvious vacuum leaks as well since those are common problems.
