Fuel System:
* Fuel Pump: A weak or failing fuel pump can't deliver enough fuel pressure, leading to sputtering and poor starting. Listen carefully near the tank for a whirring sound when the ignition is turned on. A weak hum or no sound at all suggests a failing pump.
* Fuel Filter: A clogged fuel filter restricts fuel flow, causing similar symptoms. This is a cheap and easy component to replace first.
* Fuel Injectors (if equipped): If your S10 has fuel injection (less common in '86 but possible), clogged or faulty injectors can cause sputtering. This requires more specialized testing.
* Carburetor (if equipped): If your truck has a carburetor, many issues can cause these symptoms. This includes a dirty carburetor, clogged jets, a faulty accelerator pump, or a vacuum leak. A carburetor rebuild or replacement might be needed.
* Fuel Pressure Regulator: This component regulates the fuel pressure in the system. A faulty regulator can lead to inconsistent fuel delivery.
Ignition System:
* Distributor Cap and Rotor: Worn or corroded components in the distributor can cause misfires, leading to sputtering and poor running.
* Ignition Coil: A weak or failing ignition coil won't produce enough spark to ignite the fuel-air mixture consistently.
* Spark Plugs and Wires: Worn, fouled, or damaged spark plugs and wires can prevent proper ignition. Inspect for cracks, corrosion, or excessive wear.
* Pick-up Coil (in the distributor): This component sends the signal to the ignition coil. If it's failing, you'll have weak or inconsistent sparks.
Other Potential Causes:
* Catalytic Converter: A severely clogged catalytic converter can restrict exhaust flow, leading to poor engine performance.
* Air Filter: A severely restricted air filter will starve the engine of oxygen, causing poor running.
* Vacuum Leaks: Leaks in the vacuum system can disrupt fuel-air mixture and timing, causing all sorts of problems.
* Throttle Position Sensor (TPS) (if equipped): This sensor tells the computer the throttle position, and if faulty, can lead to rough running.
* Mass Airflow Sensor (MAF) (if equipped): Similar to the TPS, a faulty MAF sensor provides inaccurate readings, impacting fuel delivery.
Troubleshooting Steps:
1. Start with the easy and cheap stuff: Check the air filter, fuel filter, and visually inspect spark plugs and wires. Replace as needed.
2. Listen for the fuel pump: See if you hear it whirring when the key is turned to the "on" position.
3. Check fuel pressure: This requires a fuel pressure gauge and is best left to a mechanic unless you have experience.
4. Inspect the distributor cap and rotor: Look for cracks, corrosion, or excessive wear.
5. Check for vacuum leaks: Listen carefully for hissing sounds near vacuum lines. Visually inspect lines for cracks or loose connections.
Recommendation:
Given the multiple symptoms, it's unlikely a single, simple fix will solve the problem. A mechanic with experience working on older vehicles can properly diagnose the issue using tools and testing equipment. Trying to guess and replace parts randomly can be expensive and time-consuming. It's best to get a professional diagnosis to avoid unnecessary expenses.
