i have an 88 4.9 L6 that i just bought for $750 last week. all i had to replace was the water pump and valve cover gasket and we did a tune up. well anyways, after i filled up the front tank, i switched to the back which had about 3/4 of a tank in it and drove around for a while and for a good bit of the next day and it didnt move so i switched back to the front tank and it was down to half a tank. does anyone know why it would display the rear tank level when i switch to it but keep pulling from the front?

 

There are some other posts here on this issue. It seems that your switch might not be working, so you were probably actually drawing gas from the front tank and not the rear. Look around, with the search feature, and see if you can find some more complete answers to your problem.

 

My 2 cents worth, if you're seeing the level change at the guage when you switch tanks, the switch is working. There is a sender in each tank that tells your guage how much fuel is in it. If it didn't switch tanks (fuel pumps), it wouldn't switch senders.

So just to get this straight - you drove on the rear tank, and the level didn't change. Switched to the full front tank, and the guage says it's at 1/2...

Sounds like the senders could be going south on you. Sometimes they'll show a full tank until it's almost empty, then all of a sudden you're on E... I'd suggest filling both tanks, and running one down to empty. Keep an eye on the guage as it goes, and see how it acts. You can set the trip meter to watch how many miles you've driven - should get 200 or so miles on a tank before it's empty.

 

well the front tank works fine cuz the gauge goes down as i drive just like it should. but the rear tank has been at 3/4 since i got it. pretty much, it draws from the front tank no matter which one i have it set to, but it DOES change which tank the gauge is displaying

 

The switch is probably switching the gauge sending unit but not the pump. The rear tank could have quit and the previous owner messed with the wiring to make it seem like both tanks were working. Pull the switch and test the pumps. Power into the switch is the red wire with a yellow stripe. The tank wires aren't marked as to which is front or rear on my diagram, but one is the red wire and one is the brown wire with a white stripe. Hook the red/yellow wire to the red wire to bypass the switch and test one pump, and then hook the red/yellow wire to the brown/white wire to test the other. Do this with the switch unplugged.