First off you should never fill the tank with the engine running as it is a safety hazard, however your description sounds like a bad purge valve. It is the piece that allows the EVAP system to burn off the fuel vapors it collects in the EVAP charcoal canister to keep it out of the air. It is supposed to stay closed until it runs an EVAP test or it want's to purge the fumes. In your case it is stuck open (common) and when you are filling the tank the fuel/air vapors in the tank are being pushed into the engine which causes it to run very rich as it tries to burn all the extra fuel. It's very easy to test and replace it. Open the hood and find the valve as shown, Remove the two hose clamps, unplug the electrical connector and remove the valve. To test it you can simply blow through it, with it disconnected you shouldn't be able to blow through it in either direction. If you can it's bad. However if it isn't sticking hard, sometimes the motions of removal will cause it to close and test good, but still be faulty. Generally I will test them on the vehicle by disconnecting the line that goes to the canister (right hand hose in image) with the engine running, and unplugging the electrical connector. If it is stuck open the engine idle will rise from the vacuum leak and you will feel vacuum at the hose port. Reverse the process to install it.
Images (Click to enlarge)
Aug 10, 2023 at 4:14 AM
