Fuel gauge not working properly

2003 PONTIAC GRAND AM

198,000 MILES • 3.4L • V6 • 2WD • AUTOMATIC

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When I first start the car of the morning fuel gauge seems fine. But as I drive it slowly drops almost a 1/4 tank. Could this be caused by a bad ground? Or is it more apt to be the sending unit? I have used 4 ounces of seafoam and a full bottle of Berrymans chemtool this evening.

Aug 11, 2021 at 6:46 PM

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SQM

CAR REPAIR CONTRIBUTOR
6,383 POSTS

Hello,

The issue you are describing is more than likely caused by the sending unit in the fuel tank.

The contact in the sending using acts a resistor, when the sending unit float goes up and down it essentially registers different resistance which translates to the fuel gauge. (see picture below)
With the constant up and down movement, over time the contact wears off and can give you incorrect reading at the gauge.

https://www.2carpros.com/articles/how-a-fuel-pump-works

Please let me know of any questions.

Thank you.

Images (Click to enlarge)

Aug 11, 2021 at 7:40 PM