99 sonoma fuel gauge problem

[99SonomaSLS]

ok so i think the problem here is my fuel sending unit but im not sure.

when i fill my truck up from empty (the gas light on) atleast this is just going by the gauge i only was able to put 11.89 gallons in the tank..everywhere online im reading say these trucks have a 18 or 19 gallon tank..


sometimes my needle to my gas gauge flutters (moves up and down)
but it never goes say from full than back to empty than back to full. i have a video if it registering as 3/4 and than going to full and past full and than back to 3/4. right when i started the truck.
can my problem be a bad fuel sending unit/fuel pump?
i think what im going to do is once the gas light comes back on im going to continue driving and see how many more miles i can drive for. and obv keep a gas tank in the back and try to run the truck fully out of gas



i managed to get 185.6 miles out of the full tank. and i felt that was kind of low i mean it does equal out to around 15.5 mpg which seems kinda in the same ballpark as what these trucks are about to get.. but the fact that i could only put 11.89 gallons in the tank really gets me confused. as if there was 6 more gallons of gas in the tank

its a 99 4.3 with 134k miles . what do you guys think my problem can be?

 

[deckley]

Had the same problen last winter. It progressed to a dead fuel pump. I'd suggest getting a new one, whole unit. Can't remember how much napa charged me, but wasn't am arm & a leg.
Changing it sort of a pain; should drop tank, but with older truck, things are probably rotted & rusted.
I mapped out where the pump is then cut a hole in the bed. Used some sheet metal to cover the hole after. A couple pop rivets & some silicone & voila!