1. The Obvious (But Important) Checks:
* Check for leaks: Visually inspect the fuel lines, filler neck, and tank for any signs of leaks. Even a small leak can significantly impact the fuel level and cause a faulty reading.
* Wait: After filling, let the vehicle sit for a while (30 minutes or so). Sometimes, air bubbles in the fuel system can temporarily affect the gauge reading. See if the reading stabilizes.
* Recheck the fill-up: Make absolutely certain the tank was truly filled to the top. A slightly low fill could contribute to the issue, though less likely to drop to "E."
2. Fuel Level Sender Unit:
This is the most common culprit. The sender unit, located inside the fuel tank, is a float attached to a potentiometer. The potentiometer's resistance changes with the float's position, sending a signal to the gauge. Problems include:
* Faulty Float: The float might be damaged, stuck, or not moving freely, giving inaccurate readings.
* Bad Potentiometer: The potentiometer itself could be worn out, corroded, or broken, leading to erratic or incorrect readings.
* Wiring to Sender: Check the wiring harness connecting the sender unit to the instrument cluster for any breaks, shorts, or corrosion. This is often overlooked but is a very common problem on older vehicles. Wiggling the wires while monitoring the gauge can sometimes reveal a bad connection.
To Diagnose the Sender Unit:
* Access the sender unit: This usually involves dropping the fuel tank (a significant undertaking), though in some cases access may be possible through a small access panel. Consult a repair manual for your specific vehicle model.
* Inspect visually: Once accessed, check the float for damage or sticking. Check the potentiometer for corrosion or damage.
* Test the resistance: With a multimeter, you can test the resistance of the potentiometer at different float positions (if you can safely manipulate the float without dropping the tank). Your repair manual will provide the correct resistance values at various fuel levels.
3. Instrument Cluster (Gauge):
While less likely, the fuel gauge itself in the instrument cluster could be faulty.
* Check other gauges: See if other gauges (speedometer, tachometer, etc.) are working correctly. Problems with the instrument cluster may affect multiple gauges.
* Test the gauge (advanced): This involves testing the gauge's circuit directly, often requiring specialized equipment.
4. Wiring Harness:
* Trace the wiring: Carefully follow the wiring harness from the fuel level sender to the instrument cluster, looking for any damage, corrosion, or loose connections.
5. Fuel Pump Relay/Fuse:
While less likely to cause a dropped needle to "E", a faulty fuel pump relay or blown fuse could lead to inaccurate readings as the pump would struggle, affecting the sender unit. Check these before replacing the sender.
Important Considerations:
* Safety: Working with fuel is dangerous. Always disconnect the battery before working near the fuel tank or any fuel system components. Proper ventilation is essential. Consider having a professional deal with the fuel tank if you're not comfortable.
* Repair Manual: A repair manual specific to your 1993 Ford Explorer will provide detailed diagrams and instructions for accessing and testing the fuel level sender unit and other components.
* Professional Help: If you are not comfortable working with automotive electrical systems or fuel systems, it's best to take your Explorer to a qualified mechanic. Replacing the fuel sender unit is a significant job and requires proper safety precautions.
Start with the simple checks, and progressively move to more complex diagnostics. The fuel level sender unit is the most probable cause, but a thorough investigation is necessary for an accurate diagnosis.
