I have a 94 Dodge Ram Van 250 with a fuel injected 318. The fuel tank is building excessive pressure and blowing fuel out the filler hose connection to the fuel tank. I have taken it to the Dodge Dealer twice now for the same problem over a 3 year period. They have replaced the O ring at the connection site as well as a new fuel cap. They check the system (assuming at idle) and say that the fuel pressure is normal. On a recent trip while driving 250 miles at 75 mph it took over a minute for the excess pressure to vent from the tank after loosening the fuel cap to refuel. The van was leaking fumes until the pressure was released. I noted fuel mileage decrease and a loss of power. After refueling and driving another 150 miles I noted the same issues and upon pulling in the driveway fuel was leaking from the filler hose at the fuel tank. The leak stopped once the pressure leaked from the tank. The Dodge deal can fine no cause and only repairs the leak issue. Something else is going on and wonder if those in this forum can lead me and my Dodge dealer to a proper correction.

 

Either the fuel pump is heating up and there by heating up the fuel and building the pressure, or you have a problem with the evap system. Instead of pulling the fuel vapor from the tank through the vapor cansister into the engine it is sending combustion gasses from the crank case of the engine back through the evap system into the tank.

 

What would the test be to determine if the vapor canister is working correctly?

 

With engine running pull the vacuum lines off of the vapor canister and see if it sucking air in or pushing air out off the side coming from the engine not the fuel tank side. Use your finger so cover the end of the vacuum hose and see if it wants to stay on your finger (good) or push away from it (bad).