2008 prostar

This truck should have the fuel transfer pump between tanks. The way it works, the engine only draws and returns to the drivers side tank. The passenger side is only a storage tank. There are is a level sensor for each tank that the body controller monitors. Once it sees the drivers side tank is down 10% lower than the passenger side, it will turn on the transfer pump to even them out again. So the fuel level should never go up on it's own in the passenger side unless the driver is fueling it. If the passenger side is staying full, this means the fuel transfer pump or level sensors aren't working right. This is body controller computer controlled and you need Diamond Logic Builder software to read and see what is going on.

 

Give me the last 8 of the vin and I will see how it was built. If it goes back to the passenger tank the fuel pump might have been eliminated or bypassed.

 

Sorry for the delay. Parts break down shows both set ups. It could have been built with or without the pump and depends on how it was ordered. Basically, if you have the pump, there is only a draw line on the right side tank. If both tanks have draw and return lines, then you DO NOT have the pump system and just regular "T" fittings for both at the back of the engine. So you are now looking for an equalizing problem. Fuel lines are oring VOSS fitting style. Check each oring at each tank fitting. Then the actual tank fitting also spins out of the tank with another oring sealing it. Check those too. You could also have a cracked pick up tube but usually when they have a problem it won't act up unit you reach a certain level in the tank. If the truck starts and runs fine, generally the suction side is ok, if not it would be sucking air and hard to start. Pick up or return tubes are welded inside the tanks and not serviceable, you would have replace the whole tank if one is cracked.