So I just finished my front tank off and got a whopping 60 miles out of a full front tank!

the last two tanks I have gotten 180-190 miles out of them, about in line with where I expected.

There are no visible leaks, and no difference in how the truck is running
but the front tank is bone dry( very hollow when tapped with a hammer) gauge does not really function on the front tank

I expected bad millage when I bought the truck 8 to 10 but there has to be something going on to get 3 mpg

The truck has had a recent tune up, all fluids changed including the diffs, plugs, cap, rotor, and o2 sensor. all to pass a smog check and I got reasonable millage out of the tank before this one ~ 180.

any ideas? I suppose I could have one tank filling the other but there is no dumping fuel like I have heard is common with that failure... does that only happen when both tanks are full?

 

Gotcha beat 40 miles rear tank 1/8

 

Start with the simple things first. Check the Fuel Pressure Regulator. Pull off the vacuum line then inspect the port for signs of fuel (smell and sight). It's very common for the regulator to develop a leak through the diaphragm which allows raw fuel to be sucked into the intake.

If you have the very common crossflow problem then the fuel from the front is filling the rear tank. Eventually the rear tank will overflow.

 

My money is on the fuel transfer problem. If the gauge on the rear tank works at all run it down to about 1/4 tank and then switch to the front and run it for a while. Then go back and check the level in the rear, if you magically have more than 1/4 tank that confirms you have the transfer problem. The fix is to replace the FDM in the rear tank.