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I just bought a 1999 Honda Civic and had to fix the gas gauge. My mechanic replaced the fuel sender unit. However, although it does seem to work, it only works about 20% of the time. Whenever I go over a hill it will float to the top and stay there. It seems to work in the morning when I first drive it but will soon float to the top. Is this normal on these cars or is the gauge still broke? Thanx