I have a 2014 Fiat 500 Sport that I bought new and it now has about 36,000 miles on it. Last week, I was trying to fill it up with gas at my usual gas station and the pump handle kept clicking off immediately--time after time. I thought it was a defective pump, so I moved my car to a different pump. Same thing happened. So, I squeezed the handle slightly (over and over again) and was finally able to get the tank full--but after about 10+ minutes of frustrating effort.
I have had considerable experience repairing our cars over the years (including engine rebulids when I was younger) and I was a R&D Engineer and Telecommunications Engineer during my working life (now retired) so I already knew where the problem with my Fiat 500 was probably hiding--the Evaporative Control System.
But it was still difficult to finally find the problem. In the Fiat Abarth Forum I found other postings complaining of the same tank filling problem. There are all sorts of horror stories of Fiat Dealer Techs "fixing" this problem and charging $700-$1500 to the customer--AND NOT ACTUALLY FIXING those cars. It appears that official those techs were stumbling around replacing the wrong parts, doing all sorts of things without fully understanding the operation of the -Evap System. Also, much of those posts by car owners were not specific enough, so I want here to carefully document the precise fix. Read on below.
Underneath the rear of the car is a large cavity, rearward of the read axle. The charcoal canister of the Evaporative Control System is mounted to the top of the underbody there. It is a somewhat large black plastic cylinder. It also has a white rectangular box mounted to it (called Dectector, Evaporative System Integrity Module). There are a total of 3 hoses (two hard plastic and one regular soft hose connected to that assembly. This is how the system works: the larger hard black plastic hose comes to the charcoal canister from the top of the fuel pump assembly, so does the smaller hard black plastic hose. The larger "regular" soft hose connects from the white box of the charcoal canister and routes around up to the inside of the right rear fender where the fuel filler is located. There is a black plastic vent at that end of the hose which is mounted inside of the fender for support.
Fuel vapor (not liquid fuel) from the top of the fuel pump assembly (which is located immediately under the bottom of the rear seat cushion) is routed down to the charcoal canister, then the fuel vapor is absorbed by the charcoal and the resulting "cleaned" air is sent via the soft black hose to the plastic vent (mounted inside of the right rear fender) for release to the atmosphere. When you fill your gas tank, the air in the gas tank has to be pushed out through this Evap System to make room for the liquid gasoline.
It is possible to have a clogged charcoal canister which would prevent the air in the gas tank from being expelled as you fill your gas tank. But that is rarely the problem (except on very old cars sometimes). Other posts described Dealer Techs replacing the fuel tank, the fuel pump assembly, hoses, charcoal canister---all very expensive for the customer and usually wrong.
On my car (and on many others with this problem) the failure was much more difficult to find--but fortunately, was not costly and was relatively easy to fix. Complicating the discovery of the problem was that there were no ODB II fault codes set by the car's computer system--therefore electrical parts, monitored by the ODB II System were likely not to be blamed.
The PROBLEM:
A mechanical "check valve" which is integrated into the fuel pump assembly was STUCK. Yep, just stuck in the CLOSED position, which prevented fuel vapors in the fuel tank from being expelled as gasoline was trying to enter as you attempt to fill your tank. This "check valve" is not electrically operated, therefore does not report to the car ODB II System and therefore no ODB II fault codes were or could be set.
The FIX:
Well, two ways I know of. Remove the bottom of the rear seat (only two bolts in the rear footwells) and slip the seat belt buckles through the back portion of the seat bottom. The rear seat back of the rear seat can stay where it is. Now, underneath the black metal plate (in the middle) is where the fuel pump is located. Take out the 4 screws and pry up the black plate (it has a seal). Now you are looking at the top of the fuel pump assembly. You will see 3 hoses. The larger hard black plastic hose goes down to the charcoal canister. The other two hard black plastic hoses--one goes down to the charcoal canister and the other is the liquid gasoline supply line that goes up front to the engine.
Take a handle end of a large screwdriver or a small rubber hammer and tap/knock on the top of the white colored fuel pump assembly. Don't be stupid and whack it so hard that you crack or break the white plastic on the top (fuel pump assembly cost is $300+). You just want to knock it hard enough to free that stuck "check valve". Give it a bunch of taps (if necessary). If you hear a rushing sound, the valve is now free and the fuel vapor fumes are now racing out of the gas tank and into the charcoal canister....now you can put the car all back together and go to the gas station.
BUT, tapping and knocking DID NOT WORK for me--the valve must have been "too" stuck. I had to take off the larger hard black plastic hose from the top of the fuel pump assembly (there is a 2 piece interlocking plastic clip assembly holding that hose to the fuel pump connector port). Then I attached a piece of regular rubber heater hose (1/2 inch?) to the fuel pump assembly connector port and blew into it somewhat hard. As soon as I took my mouth away, fuel vapor rushed out of the heater hose. SUCCESS! that meant that the stuck valve was now unstuck and regular venting of the gas tank could now take place. I put everything back together and went to the gas station....I no longer fear the gas station.
What about the FUTURE?
Well, it is certainly possible that the integrated valve will re-stick. Time will tell. What caused it to stick in the first place? Lousy design and /or manufacturing is my guess. If it sticks again, I will spend the $300 (RockAuto MOPAR OEM part) and install a new entire fuel pump assembly--just to get that blasted plastic "check valve", which is a tiny part of the assembly and is not independently replaceable.
GOOD LUCK. Other things may be causing this "can't fill my gas tank" problem. But this "check valve" has been definitely known as the cause. It was the problem on my car.
Legal Disclaimer: Use at you own risk. I am not responsible for anybody's inept attempt to repair their own car....if you do not have experience in car repair, don't do this.
Over and Out.
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