Hard To Fill With Fuel: Notes

Fig 1: EVAP System Component Identification & Location

Courtesy of CHRYSLER GROUP, LLC

We are all familiar with the handle we squeeze to get fuel to exit the nozzle. The shut off is created by an aspirator or sensing port located underneath the end of the nozzle and when fuel covers the sensing port, the nozzle shuts off.

When the fuel pump nozzle is placed in the filler cup and triggered on, fuel flows down the fill pipe. Air from the outside of the filler cup is also drawn into the filler cup due to vacuum created by the fuel flow. The air and fuel flow into the fuel tank through the inlet check valve (ICV), the valve that is welded to the fuel tank and creates the connection between the fill hose and fuel tank shell. Fuel displaces the vapor in the fuel tank, fuel vapor and the entrained air from the outside flow out of the fuel tank through the Fill Limit Vent Valve (FLVV) or a Control Valve (CV) if so equipped. The Control Valve has an internal component (diaphragm) that communicates with atmosphere through the recirculation line when the fuel cap is removed prior to refueling. The recirculation line must be free of debris, liquid or any other type of blockage in order to create the communication link. The confirmation of this link will permit the diaphragm to rise off of the main venting orifice allowing fuel vapor to exit the fuel tank.

That fuel vapor flows from the FLVV / CV through the canister line and into the evaporative canister where the hydrocarbons attach to the charcoal in the evaporative canister and fresh air exits the evaporative canister. The fresh air travels past the Evaporative System Integrity Monitor (ESIM) and through the air line and exiting the fuel system through the fresh air filter. Once the fuel level reaches full, there is a refueling float in the FLVV / CV which closes the main vapor venting orifice. The closure of this orifice prevents fuel vapor from exiting the fuel tank. The pressure in the fuel tank rises rapidly and fuel fills the filler pipe. When the fuel hits the aspirator valve in the fuel fill nozzle the fuel flow is shut off.

Every element that fuel and vapor flow through results in additional back pressure during refueling. When functioning properly, the back pressure is low enough that the fuel in the filler pipe does not rise high enough to cover the sensing port and shut off the refueling nozzle.

When a hard to fill condition is present, something has happened to cause an increase in system back pressure. The back pressure rises to the point where the fuel height in the filler pipe covers the aspirator and shuts off the fuel nozzle, or the customer can only get fuel into the tank at a very slow rate due to the additional back pressure restriction.

The "Hard to Fill" diagnostic procedure focuses on trying to efficiently identify what has created the increase in back pressure creating the hard to fill condition.

There can also be problems with fuel station nozzles and operator procedure, such as not putting the nozzle into the filler pipe properly. This can result in a hard to fill condition where constant fuel flow is not able to be established. As the customer gets used to their vehicle, the owner typically figures out the proper nozzle insertion. An issue with the fuel pump nozzle would be intermittent when they pull up to a pump with a bad nozzle, unless they always refuel at the same station / same pump and it happens to have a bad nozzle.