I have a 1988 f-150 with the 4.9 EFI engine, maual transmission. When I first bought the truck, the rear gas tank would work fine until it got down to about 3/4 of a tank. Then it would start bouncing from full to empty and about the time it got to 1/2 full, it fell to empty. The front tank worked fine. Now the front tank does the same thing. And I have noticed that if I fill both tanks,. the back tank pumps into the front tank until it is about 1/2 full. Which means the front tank runs over.
Any ideas or experience with a problem like this??