A 1992 chevy

a relitive has this chevy he clames his tank is empty .when he goes to fill it only takes 3 gallons. whats the prob they had this prob on there show. he says his gas gague does not work

he clames his tank is empty
. How does he know it is empty?

The solution on the show was, fill the tank, and set the trip-odometer to zero. Then intentionally run out of gas. From then on, the trip odometer is your gas gauge. If it ran out of gas at say 200 miles on the trip odometer, then you would need to keep resetting it each time you fill the tank, and re-fill the tank at around 150 miles on the trip od.
Most people just have a routine based on their repetitive trips back and forth to work. I just fill the tank every Monday.

It is possible your relative is right though. There are a few cars out there that for some reason cause a filling pump to shut off during normal pumping, even though the fuel tank is not even close to full. Chrysler Sebring comes to mind. If your relative is certain that the tank is mostly empty but the pump keeps kicking out, there two ways to fill the tank anyway.
First try pumping the gas with the nozzle at a different position than normal (straight in, 90 degrees). If that doesn’t work, pump the gas very slowly, and each time the pump kicks, start again very slowly. Apply a lot of pressure on the nozzle. Eventually you will be able to fill the tank. Don’t fill it all the way, just estimate how much gas you need and go a little less. If you completely fill it, gas will come gushing out of the tank and spill on your car and on the ground before you stop the pump.