Fuel gauge all over the place, please help

Tank sender unit is hosed, I'd bet. Maybe as simple as a cruddy connector or bad ground, maybe as complex as needing a new sender unit.

My Mazda 626 (an '82) had a "psycho gas gauge" for a while, too - Finally got around to pulling out the sender unit and found that the resistance wire that the float's slider moved on had broken in multiple places, , shifted around a bit, and landed so that things were sorta "crosswise", electrically speaking - In some sections, the reading was reasonable. In others, moving a tiny fraction of an inch would jump between segments of the resistance coil, causing *HUGE* changes in the level that the gauge "saw". Still other segments had no coil at all, so moving from one of the "sane" segments onto the "bare spot" would appear to go from, for instance, half a tank to dead empty in a matter of seconds, or from dead empty to 3/4 tank, etc.

Speaking of fuel gages.Is there an easy way I can tell how much gasoline is in a gas tank and the fuel gage doesn't work at all.I was thinking if I get a small diameter lenght of clear flexible tubing and if I push the tubing down into the tank and then hold my thumb over the end of the tube and then yank the tube out of the tank, that might give me a fair idea of how much fuel is in the tank. cuhulin

If the shot from the filler to the tank is straight or nearly so, you can use a dipstick. For a while when the gauge failed, I used a wooden 1X1 with my '59 F100. If you need a bit more flexibility with your car, maybe ABS sprinkler tubing might have the right balance between stiffness and flexibility. If the dipstick has to be so flexible that it curls up in the tank, this technique fails.

Counting the miles since the last fill-up is also a pretty good way to estimate the fuel.