I have a 1999 F-150 and I recently noticed that my fuel guage is fluxuating. So far its just a very slight movement. It will move only about a quarter of an inch or less but I have noticed it. Earlier this week I put on a BBK Cold Air Induction and I am not sure if that had something to do with it. The instructions were very basic and I don't think that there was anything that could have gone wrong there. I am hoping that someone can point me in the right direction.

 

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Sounds like the float in your tank is starting to go. When it does that, it starts to "sink" a little more in the gas than normal instead of sitting right on top so it moves more. BUT....First check the gauge to make sure it isn't going bad. Swing by a salvage yard and get one for cheap and swap it out to see how it performs. If it does the same, then it is more than likely the float. It not, then you have just fixed it.