1997 Pontiac Bonneville Owner's Manual - Page 129

Here are some things that some owners ask about. None of these show a problem with your fuel gage: At the service station, the gas pump shuts off before the gage reads FULL (F). It takes a little more or less fuel to fill up than the gage indicated. For example, the gage may have indicated the tank was half full, but it actually took a little more or less than half the tank's capacity to fill the tank. Boost Gage (Option) The gage moves a little when you turn a corner, speed up, or make a hard stop. The gage doesn't go back to EMPTY (E) when you turn off the ignition. 0 ms -10 If you have the large span (220") gage, the needle moves more for a given amount of fuel. This does not indicate excessive fuel consumption, and is normal. Vehicles equipped with the supercharged engine have this boost gage that indicates vacuum during light to moderate throttle an'd boost under heavier throttle. The gage displays the air pressure level in psi going into the engine's combustion chamber. The gage is automatically centered at zero psi every time the engine is started. Actual vacuum or boost is displayed from this zero point. Changes in ambient pressure, such as driving in mountains and changing weather, will slightly change the zero reading. 2-76