Fuel System:
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to stumbling, especially under acceleration. This is the cheapest and easiest thing to check first. Replace it if it's dirty or old.
* Fuel Pump: A weak or failing fuel pump can't deliver enough fuel under load. Listen for a consistent humming sound from the pump when the key is turned on (but engine off). A weak pump may be quieter or make odd noises. A fuel pressure gauge test is the definitive way to diagnose a fuel pump issue.
* Fuel Injectors: Clogged or faulty injectors can cause a misfire and stumbling. This requires more specialized tools and knowledge to diagnose; a fuel injector cleaner might temporarily help, but a professional inspection might be necessary for a proper diagnosis.
* Fuel Pressure Regulator: A faulty regulator could cause incorrect fuel pressure, leading to poor performance. This typically requires a pressure gauge test.
Ignition System:
* Spark Plugs and Wires: Worn, fouled, or damaged spark plugs and wires can cause misfires, resulting in stumbling. Inspect them for wear, cracks, or fouling. Replace them if necessary.
* Ignition Coil: A failing ignition coil can't deliver sufficient spark to one or more cylinders. A faulty coil can cause a misfire in a specific cylinder.
* Distributor Cap and Rotor (if applicable): In older 350s with distributors, these components can crack or wear, causing poor spark delivery. Inspect for cracks, corrosion, or wear.
Other Potential Causes:
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor provides inaccurate air/fuel mixture information to the engine computer, leading to poor performance. Cleaning the MAF sensor (carefully!) is a good first step.
* Throttle Position Sensor (TPS): A faulty TPS provides incorrect throttle position information, causing erratic fuel delivery.
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's timing and air/fuel mixture. Inspect all vacuum lines for cracks or loose connections.
* Catalytic Converter: A clogged catalytic converter restricts exhaust flow, leading to power loss and stumbling.
* Oxygen Sensor: A faulty oxygen sensor provides inaccurate readings to the engine computer, leading to poor fuel mixture.
Troubleshooting Steps:
1. Start with the basics: Check the fuel filter, spark plugs, and wires. These are the most likely culprits and relatively easy to inspect and replace.
2. Listen for unusual noises: Pay attention to any unusual sounds from the engine, such as ticking, knocking, or a whining fuel pump.
3. Check engine codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the engine's computer. This can provide valuable clues about the problem.
4. Visual inspection: Look for any visible signs of damage or wear, such as loose vacuum lines, broken wires, or leaking fluids.
5. Professional help: If you can't identify the problem yourself, take your truck to a qualified mechanic for diagnosis and repair.
Remember safety first! Work on a well-ventilated area, and disconnect the battery negative terminal before working on any electrical components. Improper repair attempts could lead to further damage.
