Q: My Buick LeSabre 1998 model misfires on cylinder #3.

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Buick lesabre 1998 modle misfire on #3 but when I fill the tank .the check engine light disappears and the car runs smooth .Already changed the upper intake manifold because of coolant leak and changed the fuel pump ,wires spark plugs .I don't know what else to do. But what is weird is with a full tank the car runs smoother .

My car has 186000 miles.
My car has an automatic transmission.

Hi there. The fuel is warm when the level is low and when the fuel tank is filled up the fuel tends to get cooler than it was before. In general, the fuel is low dense when it is warm and then it becomes more dense as the fuel is cooler. Your vehicle may have a fuel injector that is not working or a spark plug that is not firing when the fuel is warm, but when the fuel is cooler they tend to work. Try unplugging the fuel injector when the engine is running good and see if the engine hesitates. If the engine begins to hesitate, then I suspect that the fuel injector is clogged with tiny particles. I recommend putting in fuel injection cleaner and running the vehicle until the fuel needs filled up again. If the misfire comes back, then I recommend replacing the fuel injector on cylinder number 3. If you need further assistance with your engine misfiring, then seek out a professional, such as one from Your Mechanic, to help you.

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