1. Fuel Delivery Issues (Most Likely):
* Fuel Pump: A weakening fuel pump might struggle to keep up with demand under load when the fuel is hotter and less dense. This is especially true if the pump is already aging. Check fuel pressure at the rail (with a gauge) when hot and under load. Low pressure confirms this as a suspect.
* Fuel Injectors: Worn or dirty injectors can lead to inconsistent fuel delivery, particularly under stress. Heat can exacerbate this problem. Consider a fuel injector cleaning or replacement.
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to hesitation, especially under load. Replacing it is cheap and easy.
2. Ignition System Issues:
* Ignition Coil(s): Heat can degrade the performance of ignition coils, causing misfires under load when the engine is hot. Inspect the coils for cracks or damage. A coil test is recommended.
* Worn Distributor Cap and Rotor (if applicable): These components can arc poorly when hot, causing misfires. Replace them if they show signs of wear or corrosion. (Less likely on a '93 5.0, as many had electronic ignition).
* Ignition Module: This controls the ignition system and can fail due to heat.
3. Mass Airflow Sensor (MAF) Sensor:
* A faulty MAF sensor provides inaccurate readings to the computer, leading to a lean or rich condition under load which worsens with heat. Cleaning the sensor (carefully!) is worth a try, but replacement might be necessary.
4. Engine Cooling System:
* Overheating: While you say it *only* hesitates, a slightly overheating engine could be causing problems with the aforementioned components. Check your coolant level, hoses, thermostat, and radiator for leaks or blockages. Ensure the cooling fan is working correctly. This indirectly affects the problem.
5. Vacuum Leaks:
* Heat can cause vacuum leaks to worsen. Inspect all vacuum lines for cracks, splits, or loose connections.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-I scanner to check for any stored trouble codes. This will provide clues to the problem.
2. Test Fuel Pressure: As mentioned above, this is a crucial step.
3. Inspect and Clean: Visually inspect all components mentioned above. Cleaning the MAF sensor and replacing the fuel filter are good starting points.
4. Test for Vacuum Leaks: Use a vacuum gauge or smoke test to identify any leaks in the intake system.
Important Note: Working on a fuel system involves working with flammable materials. Always take proper safety precautions. If you're not comfortable working on your car yourself, take it to a qualified mechanic. They have the tools and experience to diagnose the issue accurately and efficiently.
