Need help on fuel gauge

Can any one tell whats wrong with my fuel gauge on my 98 rodeo, fuel gauge already empty, and the light start blinking after driving for only 160miles regular driving and i dont use A/C. and every time I fill it up it only goes to 13gl. I think the tank should hold 19 or 21? Does any one have same problem, or what parts need to replace.

Thanks

This is a common defect on 2nd Gen Rodeos. Usually, it requires replacing the entire fuel pump module but you can get just the sending unit from St. Charles Isuzu. Google the name. still requires dropping the tank to fix but the sending unit is only about $30 as opposed to several hundred for the fuel pump module.