2001 Buick Century. Fuel gauge didn't work. I bought a new fuel pump with fuel level sensor on it, installed, car will not start. I replaced the fuel pump relay, put the OLD fuel pump back in with the new fuel level sensor on it, care won't start. I took offf intake to throttle body, squirted starting fluid in it, car will start. I never hear the fuel pump running. Any advice?

Most fuel pumps today are sold as module assemblies which includes the hanger, pump and level sensor. The level sensor is the device used to report the fuel level to the fuel gauge. Fuel level sensors work by attaching a float to the fuel level sensor arm; when the fuel level lowers so does the float which in turn moves the sensor arm and changes the signal. Level sensor floats can be rather bulky when attached to the level sensor arm so often times they are not pre-installed at the time of the part sale. Once the new part is removed from the box, the float (whether a new one is provided or simply removed from the original unit) must be installed onto the new level sensor arm prior to fuel pump module assembly installation. If a float is not installed, the metal level sensor arm will not be suspended at the fuel level which results in an "empty" fuel gauge reading. You can read more here: https://www.yourmechanic.com/article/why-fuel-pump-replacements-can-be-tricky-by-marvin-sunderland

The level sensor is in the fuel tank. If you replaced the pump, make sure the sensor wire is connected at the tank.

The sending unit for the gauge would have been attached to the fuel pump in the tank.

Most likely a defective fuel level sending unit, located inside the tank connected to fuel pump assembly. Theres a possibility that you have a ground issue. So check that first as its easier. If the grounds check out then you have a few options. 1. Pull the fuel pump assembly and clean off the fuel level sender(tons of tutorials online for this). This fixed my problem for 10 months until my pump went out. 2. Replace just the fuel level sender. 3. Replace the entire fuel pump assembly (which should include sender and fuel pressure sensor). And a couple notes. If you have around 100K or more miles then DEFINITELY change the entire assembly. It beats having to do all the work again in the near future. No matter what route you go be sure to replace the fuel pump tank gasket.

It sounds like your Fuel Level Sending Unit, usually located with the Fuel Pump inside the gas tank, has gone out. The Fuel Level Sending Unit sends the signal to your ECU, and then it goes to the Fuel Level gauge. Replace the Fuel Level Sending Unit and your gauge should be back to normal.

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fuel lvel sensor is bad replace the fuel pump assembly,i work for GM

If you mean the fuel level sender for the gauge it is part of the fuel pump module inside of the fuel tank. If you mean the fuel tank pressure sensor for the EVAP emission system it is located on top of the fuel pump module on the outside/top of the tank. If you have an erratic fuel gauge then the sender is most likely at fault. Some are serviced seperately but some are sold only as part of the pump. If you have to remove the tank and pump to replace the sender and have close to 100k on the odometer then I would STRONGLY suggest replacing the fuel pump at that time.

Gm cars are common for having defective fuel tank sending units in the tank. Yours likely needs replaced.

fuel sending unit is faulty needs replaced unfortunatly you will be forced to buy the entire fuel pump (module). they are not cheap.