Fuel gauge not working properly

Tiny
SBMISRY
  • MEMBER
  • 2003 PONTIAC GRAND AM
  • 3.4L
  • V6
  • 2WD
  • AUTOMATIC
  • 198,000 MILES
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.
Wednesday, August 11th, 2021 AT 6:46 PM

1 Reply

Tiny
SQM
  • MECHANIC
  • 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.
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Wednesday, August 11th, 2021 AT 7:40 PM

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