* Pump itself failing due to heat: The most obvious reason. The pump's internal components (motor windings, seals) may be deteriorating with age and heat. When the engine warms up, the internal temperature rises causing the pump to fail, while it can still manage to function when cold.
* Internal wiring or connections overheating: Wires within the pump housing, or the connections to the pump itself, might be poorly soldered or corroded. Heat expands the metals, increasing resistance and potentially causing an open circuit. This is more likely if you've noticed any unusual smells (burning insulation) around the pump.
* Fuel pump relay (even with replacement): While you've replaced the relay, it's possible:
* The new relay is faulty: Test it with a multimeter to ensure it's switching correctly under load.
* The relay's wiring is faulty: Check for any loose connections or damaged wires in the circuit leading to and from the relay. Heat can exacerbate these issues.
* Something else is overloading the relay: A short circuit or excessively high current draw from a component in the fuel pump circuit could overheat and cause the relay to fail when hot.
* Fuel pump resistor (if equipped): Some systems use a resistor to reduce current during pump operation. This resistor could be failing due to heat, causing the pump to not receive sufficient power when warm.
* Insufficient fuel cooling: If the pump isn't adequately cooled by the fuel itself, or ambient air, it might overheat and stop working. A clogged fuel filter or restricted fuel lines can raise fuel temperature.
* Grounding issue: A poor ground connection can lead to increased resistance and overheating, particularly when the engine and surrounding components heat up.
Troubleshooting Steps:
1. Check the fuel pump's temperature: This is difficult, but if you can feel the pump after a warm-up cycle, a significant increase in temperature suggests an internal problem.
2. Thoroughly inspect all wiring: Look for chafing, corrosion, loose connections, or any signs of melting on the wires leading to and from the fuel pump, and the relay. Pay close attention to the ground wire.
3. Test the new fuel pump relay: Make sure it is functioning correctly. A multimeter is the best tool for this.
4. Check for voltage at the pump: With the engine warm, measure the voltage at the fuel pump's power connector. Low voltage indicates a problem in the wiring or relay. No voltage is likely a relay problem or bad wiring.
5. Inspect the fuel filter: Make sure it's not clogged, as this can restrict fuel flow and increase its temperature.
6. Consider a thermal cycling test: Run the engine until the pump fails. Let it cool completely, and then try again. This can pinpoint a heat-related failure.
If after these checks you are still having trouble, it is highly recommended to seek the assistance of a qualified mechanic specializing in classic Corvettes. This can save you time and potentially prevent further damage. Fuel pump issues can be frustrating to diagnose, and having an expert's eye is valuable.
