* Disconnection of the Fuel Level Sender: The fuel level sender is a component located within the fuel tank that measures the fuel level and sends a signal to the gauge. It's often very close to the fuel pump. During the fuel pump replacement, the sender could have been accidentally disconnected, damaged, or its wiring harness disturbed. This is the most likely culprit.
* Damaged Wiring: While working around the fuel tank and pump, you may have inadvertently pinched, cut, or damaged the wiring to the fuel level sender. Check all the wiring carefully for any breaks, fraying, or loose connections.
* Bad Fuel Level Sender (Coincidence): It's possible the fuel level sender failed around the same time as the old fuel pump, and the pump replacement was just coincidental. This is less likely, but still a possibility.
* Grounding Issue: A poor ground connection somewhere in the fuel gauge circuit could also cause the gauge to malfunction.
* Instrument Cluster Problem (Less Likely): Although less probable, a faulty gauge cluster itself could cause the gauge to fail. This is less likely since the problem arose after the fuel pump replacement.
Troubleshooting Steps:
1. Check the Fuel Level Sender Connection: Access the fuel tank again (safely!) and carefully examine the connection to the fuel level sender. Ensure it's securely plugged in. Look for any signs of damage to the connector or wiring.
2. Inspect Wiring Harness: Follow the wiring harness from the fuel level sender to the instrument cluster. Look for any damage, cuts, or loose connections along its route.
3. Test the Fuel Level Sender (Advanced): This requires a multimeter. You can test the sender's resistance to verify it's working correctly. The resistance should change as you move the float arm (if you can access it without removing the tank). Consult a repair manual for your specific vehicle for the correct resistance values.
4. Check Ground Connections: Locate the ground wires related to the fuel gauge circuit and ensure they are clean and securely connected.
5. Check the Fuel Gauge Fuse (If Applicable): Check your owner's manual or fuse box diagram to see if there's a dedicated fuel gauge fuse and make sure it hasn't blown.
If you're not comfortable working with the fuel system or electrical components, take your vehicle to a qualified mechanic. Working with gasoline is dangerous, and improper repairs can lead to fire hazards.
