Diagnosis And Testing - Hard To Fill With Fuel

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.

DIAGNOSTIC PROCEDURE 

1. Verbally confirm customer complaint.
   • Has the vehicle always had this issue, or is it recent?
   • Does it occur on all fill ups or is it intermittent?
   • Is the issue only on high flow and is it okay on low flow of the fuel pump?
2. Scan and record any fuel related P Codes.
3. Line Check  - Put vehicle up on hoist and examine visually, by feel or mirror to look for a kink, bend, or twist condition in the Fill Hose, Air Line, Recirc Line, or Canister Line. Check that the Air Line is connected to both the ESIM and the Air Filter.
   • Were any problems found?
   • No  - Continue to Step 4
   • Yes  - For a disconnected Air Line, replace the ESIM and Canister and proceed to Step 10. For a kink, bend or twist, straighten or replace as necessary, document on the repair order, and proceed to Step 10 - Fuel Fill Verification
4. Air Filter Check  - Disconnect the air filter and tap it on a table to determine if the air filter is dirty or plugged.
   • Were any problems found?
   • No  - Continue to Step 5
   • Yes  - Replace Air Filter. Remove the gas cap and tap it on the table to see if it is dirty and replace it if it is. Proceed to Step 10 - Fuel Fill Verification
5. Recirculation Line Check  - Remove the recirc line from the fill neck and remove the large fill hose at the fuel tank. The gas cap should still be on. Blow air into the recirc line and air with no contamination should flow freely out of the fill large fill hose.
   • Were any problems found?
   • No  - Continue to Step 6
   • Yes  - Replace fuel filler neck and proceed to Step 10 - Fuel Fill Verification
6. Fuel Tank Inlet Check Valve (ICV) Check  - The fill hose should already be removed from the ICV. Visually look inside the ICV for an obstruction. If obstructed, remove the object if possible. Using a long thin object (not a screwdriver) that will not damage the seal on the check valve or the antisiphon features inside the ICV, push the object into the ICV to verify that it is free of obstruction. There is a spring behind it, so there will be a little resistance, but it should move freely and not be sticky.
   • Were any problems found?
   • No  - Continue to Step 7
   • Yes  - If an obstruction was found, but the ICV moves freely proceed to Step 10 Fuel Fill Verification. If the ICV does not move freely, replace the fuel tank and proceed to Step 10 - Fuel Fill Verification
7. Reassemble the components removed in earlier steps.
8. Canister Weight Check  - Remove the heat shield and take the lines off the canister, disconnect the electrical and take the canister and ESIM assembly off the tank. Use a weight scale such as one for shipping parts or mail to weigh the assembly. A canister on a 26 gallon tank assembly should weigh less than 2700 grams (5.9 pounds). A canister on a 32 gallon assembly should weigh less than 2500 grams (5.5 pounds).
   • Were any problems found?
   • No  - Continue to Step 9
   • Yes  - Look into the ESIM ports to see if the ESIM floats have any appearance of rust or dirt. If the ESIM float is clean, replace the canister. If the ESIM appears to have rust or dirt, replace both Canister and ESIM. Proceed to Step 10 - Fuel Fill Verification
9. Nothing found in Step 1 through 8, reassemble and components removed in earlier steps and proceed to step 11.
10. Fuel Tank Refuel Check with Problem Identified and Repaired - Take the vehicle to the gas station and determine if it fills cleanly.
    • Fuel tank fills clean - Problem found and complete
    • Still Hard to Fill - Return above to the step below where you found an issue and continue diagnostic.
11. EVAP System Check  - Disconnect the vapor line on the fuel tank control valve (CV) Take the vehicle to the gas station and determine if it fills cleanly.
    • Fuel tank fills clean - Replace the canister and ESIM assembly and refuel to verify problem solved.
    • Still Hard to Fill - Move to Step 12
12. Recirculation Check  - Reconnect canister at the control valve and disconnect the recirc line at the control valve. Take the vehicle to the gas station and determine if it fills cleanly.
    • Fuel tank fills clean - Replace the recirc line and the fuel filler pipe and refuel to verify problem is solved
    • Still Hard to Fill - Replace the fuel tank and refuel to verify the problem is solved.