Hey Everyone,
I have had fuel tank issues ever since I bought my 91 E-350 460 a few years ago. The short of it: I suspected heavy rust in both tanks and for starters replaced the midship tank about a year ago. I also replaced the frame rail fuel pump and the selector valve. After doing all of this I just decided to run the van for a while only using the midship tank. It ran fine! I would every now and then switch over to the rear tank just to try to use up some of the gas in it as I knew I was going to soon replace it. I finally got around to replacing the rear tank last weekend and I also replaced the sock filter on the bottom of the in-tank fuel pump cause it was gross. I then put about 5 gallons of gas in it and it drove great however I noticed that the fuel gauge was showing about half tank full and never really dropped as I was driving it. It eventually ran out gas and sputtered out on me even though the gauge never moved (yes the gauge worked perfectly before I replaced this tank). So after the van sputtered out I switched to the front tank and noticed the gauge went to almost E when I knew I had some reserve fuel in that tank - weird but it did start back up and get me to the gas station. I filled both tanks - oddly the rear tank only took like 11 gallons (aint it a 22g?). I've now been driving around on the rear tank - the gauge is pegged beyond Full and never goes down. I've driven it about 50 miles with no gauge movement. The weird thing is - when I switch to the front tank the gauge does drop down to about the half way mark (I filled this tank up completely full when I was at the gas station!). Its as if I'm running on the front tank even though the switch is selected to the rear tank. I have not experienced the weird "overflowing" issue that many others have though (yet). ---> So the only thing I did was replace the rear gas tank and this issue arose. Perhaps the in-tank fuel pump in this tank got screwed up somehow when I was changing the tank? Any ideas? Should I just lower the tank and replace the fuel pump to rule it out?

 

The fuel pump doesn't work the gauge. The sending unit does. In these vans I believe they can come separate from the fuel pump (Not positive since its been years since I bought one for an old '88 E-250). Its odd that the mid tank is giving an issue if you haven't messed with it. And yeah that rear tank is around 20-22 gallons. I did have the selector switch in the cab get corroded so I had to disassemble it and clean it up.