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Thread: Difficulty Filling Gas Tank

  1. #1
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    Difficulty Filling Gas Tank

    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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  3. #2
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    I had my evaporators canister replaced, under warranty. Took care of the issue. One of my other cars had the same issue. It happen only at one gas station, I use always. Took it to another station. It filled fine.

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  5. #3
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    Even though the canister is rarely the cause of this type of problem (especially on newer cars), I did first check my Evap Canister by separately disconnecting those 3 hoses and blowing air through it. There was no resistance to air circulating through it at all, so the problem was elsewhere. It is also rare for gas station pumps to fail to properly dispense gasoline, but it can happen.

    But it looks like the most likely cause is failure of that integrated plastic "check valve" inside the fuel pump assembly. There are several other posts from other owners where that valve stuck.

  6. #4
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    Thanks for the post. Any photos?

    Part of the problem is in definition. There several parts that can be called rollover valves. Rollover valves simply seal the tank, should the car, well, roll over. I'd love to hear more because, though there's lots of anecdotal evidence, I can't find photos or a full description of the system. (There is one excellent description on this site, but not specific.) BTW, these problems pop up across all brands of cars, time to time, but it seems the 500 is a bit more prone. (We had a new Ford van that had this problem from day one and Ford's response was it was "normal" to have to twist the nozzle upside down, halfway out, and spend 15 minutes filling the tank.)

    Possibly the most common problem, on the Fiat, is the valve at the bottom of the filler neck. If this sticks fully closed no fuel gets in. This is the part that's freed by rapping at the base of the filler neck, or pressed free with a screwdriver inserted thru the top of the tank. I know a mechanic that presses them free with a flexible shaft inserted thru the filler neck when a customer comes in. The first time is free and had a Toyota that came in every few months until they had the neck replaced. I think this may be caused by fuel deposits on the valve.

    There is at least one other valve (one person said 3) that are part of the fuel tank. This is part of the Evap system. It blocks that exit... and is supposed to block fuel from entering the Evap tubing (and into the canister) if fuel sloshes. Good call on blowing down the line to the canister. This seems to be the "go to" for dealerships... replace the fuel tank. While yanking it, they probably bump the filler neck enough to pop that valve loose.

    There is also vent tube from the tank to the top of the filler neck. This exit is guarded by an electro-mechanical valve mounted an inch below the filler tube neck. It allows air to vent to the top of the filler neck while adding gas. I'm unsure if the electro connection is for a sensor, or if it is cut off when the ignition is on.

    I have pix of common tank mounted valves, but none specific to the Fiat tank. You are correct. These tank mounted ones are plastic parts and should be replaceable, but they usually require replacing the fuel tank on any car... a stupid idea. GM makes some of theirs replaceable but doesn't sell the parts. (Aftermarket provides a nice metal replacement for those.) Chrysler (and later FCA) seems to have decided to fuse the parts to the tank.

    I found photos of the fuel pump and I didn't see the pump containing the Evap check valve??? Do you have diagrams you could share? Is it possible the air pressure "popped" the tank check valve? BTW, you might try applying low pressure compressed air, instead of blowing on tubes.

  7. #5
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    map:

    I took off the right side rear wheel and then partially removed the plastic inner fender and did not see any other hose going to the top of the fuel filler neck area on the inside of the fender. Nothing I saw came directly from the fuel tank to that area. There is that black plastic Evap Vent (officially called FILTER, Fuel Filler Vent) mounted for support to the top of the fuel filler neck assembly. That soft black hose starts there and runs down to the white plastic box (called Dectector, Evaporative System Integrity Module) which is mounted to the black plastic charcoal canister. Originally, before I removed that Detector from the charcoal canister and tested it, I thought that was a solenoid valve of some sort blocking fuel vapor from being cleaned and then expelled from the charcoal canister to the Fuel Filler Vent. But I found 4.5vdc at the electrical connector and realized that it was a sensor. Remember--I had no ODB II codes set, so that sensor was judged OK by the car. By the way, that sensor "rattles" because it has a left/right sliding plug that must be moved by air pressure. The car's ODB II System wants to know the position of that sliding plug as the Evap System operates. But again, I had no ODB II codes set.

    As far as the fuel tank itself, I went to the Alpha Romero Dealer (which has been renamed since they no longer sell Fiats) and got the official Fiat exploded diagram of the fuel tank, fuel pump and other parts in the system. That fuel tank diagram does not show any internal valves or any hoses directly connecting to it (or hose ports for connecting hoses--other than the fuel filler inlet hose of course). I thought about removing the fuel inlet hose when I was under the car just to see what the port into the fuel tank was all about--but I did not. The fuel tank diagram does have a line running across the middle of the fuel tank filler opening--that may imply that there is a plastic butterfly valve at the input to the fuel tank that pivots around a central axis. So, it is possible that the "valve" that I unstuck by blowing into the hose connection port at the top of the fuel pump (the hose connection that is there to connect that black hard black plastic hose that ultimately goes down to the charcoal canister) is not in the fuel pump assembly. But that would mean that if it exists, a large 2+ inch butterfly valve located at that position would have to stick so rigidly closed that fuel pressure from the gas station fuel pump would not swing or force it open to allow fuel to enter the car's gas tank.

    It seems to me that the problem is not getting liquid gasoline into the fuel tank per se at the inlet opening of the fuel tank, but expelling the air in the gas tank to allow fuel to occupy that space and therefore enter normally.

    Anyway, I still do not completely understand the design of the entire Fiat Evap System, but I do know that blowing into the fuel pump Evap Port on the top of the fuel pump assembly (using a spare length of heater hose that I have) definitely freed up some Evap System valve and immediately allowed me to fill the gas tank normally. It took no parts and only cost the time to figure this out and do the work.

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  9. #6
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    Thanks... excellent description. I'd love to see that schematic some time. I wonder if it'll be in Mopar's $200 DVDs, or if they'll gloss over that section like they did for the early 2000's Dodge PU.

    The vapor hose connects to the smaller metal tube, right? Thanks for verifying the check ball and sensor.
    Attachment 35133
    Last edited by map; 09-24-2019 at 01:24 PM.

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    map:

    After freeing the sticking the "check valve" as I call it, I was only able to fill my gas tank normally 7 times--and then--the blasted thing stuck again. So my friend and I went much further in investigating the whole Evap System. We took apart much more and I have many photos with captions (attached). This time I took off the fuel filler hose at the gas tank input and got a good look. At that input, the gas tank has what I will call a "butterfly valve" that is lightly spring loaded. As fuel comes down the fuel filler neck from the gas station pump, it pushes that valve open to allow fuel to enter (that assumes air can vent from the tank as the fuel flow from the gas pump tries to push it open). I have attached a photo of that gas tank "butterfly valve".

    It turns out that a couple of things I previously posted were not correct and so I will correct those here. On the fuel pump, the larger of the two hard black plastic hoses does not go to the charcoal canister as I originally posted--instead that hose goes forward to the engine compartment. So, the three hose connections to the top of the fuel pump are: (1) large soft rubber hose is a fuel vapor hose and it goes directly to the charcoal canister assembly. (2) the larger hard black plastic hose goes forward to the engine compartment (3) smaller hard black plastic hose goes forward to the engine compartment and carries gasoline to the engine.

    Another correction: There is a smaller hose/metal tube connection on the backside of the fuel filler vent tube/hose. It was hiding behind the larger fuel filler tube/hose and I did not see it the first time. A hard black plastic hose comes from the engine compartment all the way back to the fuel filler neck area. As it gets near the fuel filler neck assembly, that hose connects to an electrical solenoid. Then out of that solenoid, a hard metal tube merges into the metal fuel filler neck. But as I posted earlier, neither that hard plastic hose or the metal tube connects to the gas tank. The gas tank has only 1 direct hose connection--the fuel filler hose. The other 3 hose connections are made to the top of the fuel pump assembly, which then mounts into the top of the gas tank.

    We spent considerable time in looking at it all.

    Here are the first batch of photos. The site is not allowing me to post more than 3 photos per post, so I will make several separate post to get all 10 photos posted.

    20191012_120925.jpg
    Top of fuel pump showing all three hose connections, with a bit of heater hose connected to the large port to allow me to blow into it and un-stick the fuel pump check valve.



    Close up of top of fuel pump showing Fiat part number (68070715AB) and manufacturing date stamp.



    Close up of the backside of fuel filler neck, far end of the charcoal canister vapor hose (going up) and its cylindrical black plastic fuel vapor vent. Large black pipe (going down) is the metal fuel filler pipe to the gas tank.
    Attached Images Attached Images
    Last edited by jwp2014Fiat500Sport; 10-13-2019 at 11:26 AM.

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    Here are some more photos. I am having problems getting these photos posted to this thread. I had to rotate my original photos to get the images to post correctly without the site cutting off some of the photo. Tilt your head to get oriented. These are photos of my 2014 Fiat 500 Sport of the Fuel Tank and Evap System -- inside the right rear fender area.


    Another view of the inside of right rear fender (inner fender removed) showing electrical fuel vapor solenoid and associated connections. "Into" is a hard black plastic hose, "Out Of" is a metal pipe which merges with the metal of the fuel filler neck.


    Another view showing the electrical fuel vapor solenoid and associated connections.
    The "Into" is a hard black plastic hose which comes all the way back from the engine compartment,
    "Out Of" is a metal pipe which merges with the metal of the fuel filler neck.


    Close up of the backside of fuel filler neck, far end of the charcoal canister vapor hose (going up to the right) and its cylindrical fuel vapor vent. Large black pipe (going down and to the left) is the metal fuel filler pipe to the gas tank.
    Attached Images Attached Images
    Last edited by jwp2014Fiat500Sport; 10-13-2019 at 11:54 AM.

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    Thank you. These are the best I've seen.

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    Here are some more photos. I am having problems getting these photos posted to this thread. I had to rotate my original photos to get the images to post correctly without the site cutting off some of the photo. Tilt your head to get oriented. These are photos of my 2014 Fiat 500 Sport of the Fuel Tank and Evap System -- inside the right rear fender area.


    Close up of the rubber hose portion of the fuel filler neck where it connects to the input port of the gas tank.
    This is the only direct connection to the gas tank. No other hoses connect to the gas tank. All other hoses connect to the fuel pump assembly.


    Close up of the inlet to the gas tank,. The red ring is the rim of the spring loaded "butterfly valve", which depresses inward easily as gasoline flows down the filler neck into the gas tank. This is the only "valve" in the gas tank assembly.
    Attached Images Attached Images
    Last edited by jwp2014Fiat500Sport; 10-13-2019 at 11:57 AM.

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