When replaced fuel pump 3 months ago no problems now gas gauge work at all when starting up then next time works but chimes and fluctuates while driving what is the problem?

The problem is unlikely to be directly related to the fuel pump replacement three months ago, unless something went wrong during that installation. The intermittent operation of your gas gauge, along with the chimes and fluctuation while driving, points to a problem in the gauge's circuitry or its connection to the fuel sender unit.

Here are some likely culprits:

* Faulty Fuel Sender Unit: This unit is located in the fuel tank and measures the fuel level. A faulty sender unit can send erratic signals to the gauge, leading to inaccurate readings and fluctuations. This is the most probable cause given your symptoms.

* Wiring Issues: Corrosion, a loose connection, or a damaged wire between the fuel sender unit and the instrument cluster can interrupt the signal. Check the wiring harness for any breaks, chafing, or corrosion, especially near the fuel tank.

* Instrument Cluster Problem: A malfunctioning gauge itself in the instrument cluster is possible, although less likely than a sender unit or wiring problem.

* Grounding Problem: A poor ground connection somewhere in the circuit can cause erratic behavior.

* Fuel Pump (Remote possibility): While the fuel pump replacement is unlikely to be the direct cause, it's possible that a connection near the pump was disturbed during the installation. It is much less likely, however, than the other possibilities mentioned above.

Troubleshooting Steps:

1. Check the Fuel Sender Unit (Most Important): This is often the source of these issues. You'll likely need to drop the fuel tank to access it (depending on your vehicle). Inspect it for damage and consider replacing it.

2. Inspect the Wiring: Carefully examine the wiring harness from the fuel sender unit to the instrument cluster. Look for any damaged, corroded, or loose wires. Repair or replace as needed.

3. Check the Ground Connection: Trace the ground wire from the fuel gauge circuit and ensure it's clean and securely connected.

4. Have the Gauge Tested (Least Important): If the wiring and sender unit are okay, the instrument cluster's gauge itself could be at fault. A mechanic or auto parts store might be able to test it.

Important Note: Working on the fuel system can be dangerous due to the flammability of gasoline. If you're not comfortable working on your car's fuel system, take it to a qualified mechanic. They have the tools and expertise to diagnose and fix the problem safely.