Can't fill tank, usual fixes didn't work!

I was wondering if anyone with more mechanical/Prius knowledge could help me troubleshoot what’s wrong with my car. It’s a 2006 Prius, with about 66,000 miles on it. In the past 8 years, I’ve never had any problems with it – but for the past two months, I’m been having two separate (but related) problems, described below. I've searched google and this subreddit extensively, and can see that similar questions pop up often - but so far, none of the usual fixes have worked!

1. No matter how much gas the car needs, when I try to refuel, the pump shuts off automatically after about 4 gallons. When I try to add more gas, the auto-shutoff is triggered immediately – so to fill the tank, I have to stand there “pumping” the lever over and over and over for about 10 minutes, as I fill the tank .02 gallons at a time. (To answer a question Toyota asked - this happens at all gas stations, and I’ve had multiple other people try pumping my gas for me, so I know it’s not user error.)
   
   
2. The fuel gauge is no longer accurate. For the past 8 years, the bars on the digital fuel gauge (which each represent about 1.2 gallons) have gone down about every 50 miles or so. Now, the first bar takes forever to go away, and the other bars go down at random intervals. The last time I filled up, the gauge still read “full” even though I had driven for 165 miles. The rest of the bars go down at random intervals – sometimes after 10 miles, sometimes after 30, 40, or 60ish miles. There’s no pattern to this (I’ve been keeping track for the past 4 fill-ups, and it’s been different every time).
   

Both of these problems happened for the first time after I tried to "top off" the tank before a big trip. I had driven less than 100 miles since my last fill up, and still had 8/10 bars on the fuel gauge. I added about 2-3 gallons of gas, and noticed that the fuel gauge didn't go back to "full" when I turned the car back on. However, it went up after about 5 minutes. The above problems occurred the very next time I filled up (at the end of a long drive, when the car needed about 7-8 gallons), and have happened ever since (over the course of 2 months, and about 3,000 miles). I've read about the 2nd problem (with the fuel gauge) happening with other cars after topping-off, but from everything I've read online, it sounds like simply recalibrating the fuel sensor/gauge would have fixed this (it hasn't).

Luckily the car’s computer displays my MPG – and this calculation is based on the miles driven, and the gas actually flowing through the fuel injector, so it’s completely accurate. When I need to get gas, I look at the MPG, and divide it by the number of miles driven, to find out exactly how much gas I’ve used. I then stand at the pump and force the exact amount of gas needed into the tank, as described in #1 above. (Thanks to this method, I've never run out of gas - but this problem is incredibly annoying, and means that every trip to the gas station takes about 15 minutes.)

So far, Toyota is stumped. When I first brought the car in, they ran a diagnostic, and gave me a new fuel neck filler valve (from my own reading, I can see that the 2004 Prius was having the gas-pump-auto-shutoff problem, and this was the official fix from Toyota… so they must have assumed my car was doing the same thing). However, this didn’t fix either problem. They then took the entire fuel system apart, inspected it, put it back together, and gave me a new gas cap (because mine was “breathing a little funny”). This resulted in me successfully filling the tank once and then the problem came back.

Next, they took out the fuel canister, ran it through some tests, and said it was working perfectly normally. Then, they took out my entire gas tank, and replaced it with a gas tank from another Prius. However, this still didn’t fix the problem – so the problem doesn’t seem to be with the tank itself or with the internal bladder. Throughout all of this, I’ve also recalibrated the fuel gauge myself using these instructions, but that doesn’t help either.

In summary, we’ve already ruled out the following:

1. Recalibrating the fuel gauge
   
   
2. Fuel neck filler valve
   
   
3. Gas cap
   
   
4. Gas tank and bladder
   
   
5. Fuel canister (haven’t tried replacing it, but they took it out and examined it, and it "performs normally in testing")
   
   
6. User error
   

Problem #1 temporarily went away for one fill-up, right after the mechanics took everything apart and put it back together - and then the problem started happening again.

Any other ideas? Over the past two months, I’ve wasted an incredible amount of time and energy trying to get this fixed!

 

I haven't done extensive testing on that - I usually keep forcing fuel in so that I know the tank is full, because filling all the way up and monitoring my MPG is currently the only way of keeping track of how much fuel is left. However, the first few times it happened, I left the gas station after only 4 gallons went it, and then drove to a different gas station later in the day, and got about 2 more gallons in. So it seems like whenever I buy gas, I get a short amount of time where fuel goes in normally, and then the auto shut-offs begin (usually after about 4 gallons have gone in).

 

The "4 gallons" thing is just an estimate, though - sometimes it *does* just stop after one gallon!

I've read a lot about the bladder problem, which seems to be common. However, we've already ruled out the bladder, since the mechanic replaced the entire tank/bladder assembly for me about 2 weeks ago - which didn't help at all. Luckily I wasn't charged for it - he just swapped it out from one of the dealership's cars so we could test it (and he'll put the old tank back in the next time I bring it in).

 

1. Between 1/4 - 1/2 tank left (around 3 or 4 bars remaining)

2. 300ish

3. Maybe 10? I'm living out of state for work at the moment, so I drive about 500 miles each weekend so I can spend time with my family. I've tried a LOT of gas stations, in different states!

4. Before this problem started, I used to let it go automatically (assuming I was at a gas station that had the little tab on the trigger to let me do this). Now, if I'm at a gas station like that, I can let it go automatically for the first 1-4 gallons, and then it shuts off. Then I I have to stand there and hold the trigger down myself (pulling it over and over and over) in order to get any gas in.

5. I've always put the nozzle in as far as it needs to go for the rubber part to get a good seal. However, since this has been happening, I've tried readjusting it -pulling it further out, pushing it further in, jiggling it around. Nothing makes a difference.

Thanks! Before trying this myself, I'll have to ask the mechanic if he's done it yet. (Since he already took the entire fuel assembly apart, and swapped my tank for another one, I'm wondering if they had to use a fuel canister to transfer the gas.)

I'm not sure, but I'll find out. Thank you for the suggestion!

 

Thank you everyone, for the advice! I now have an official "engineering ticket" open at Toyota, so it's not just the one individual mechanic working on it anymore - and after reviewing all of the information, the engineers have agreed that there's something very wrong, and this is far beyond the usual problems with the bladder or with overfilling. Toyota is now working with the dealership mechanic, to tell him which parts to test next.

I'm going to bring it in on Tuesday, and they're going to try giving me a new "fuel neck filler assembly" (before, they had only replaced the fuel neck filler valve). I think this should include many of the valves that exstudent suggested. In addition, I mentioned to the mechanic that I had posted here, and he asked me to bring in a list of everyone's suggestions.

To address a few of the suggestions directly:

I'm not overfilling it. I've owned the car for 8 years, always fill the tank completely, and have actually kept a record of every fuel purchase I've ever made over at fueleconomy.gov (I'm a huge nerd) - so from the very first time this happened, I knew exactly how far I had driven since my last fill, and exactly how much gas was needed to fill the tank. From looking back on this data, I have concrete evidence that the car has been behaving very differently in the past 2 months, as compared to the previous 8 years.

For the life of the car, I've always driven about 300-400 miles before buying gas. At that point, there are typically 2 or 3 bars left on the fuel gauge, and the pump automatically shuts off after I add 7 or 8 gallons. I've *never* try to "top it off" to get the fuel to come to an even price or anything like that - I've only put in exactly what was required to get the pump to shut off. When I said that I "topped it off" before all of this started happening, I meant that I had only driven about 100-150 miles since my last fill-up, and added an additional 2 gallons of gas before making a long drive. (That was the one and only time I've ever done that, and if there's even the slightest chance that that broke something, I really regret it!)

I currently live 260 miles away from my fiance, and drive home to see him almost every weekend. The problem that I'm having is that I'm routinely driving over 400 miles at a time without filling up, and when I go to buy gas, the pump shuts off after only 4 gallons. If I stop filling then, and look at the fuel gauge, it says that the tank is only half full.

Surely, my 2006 Prius is not suddenly getting over 100 miles per gallon! (especially when the computer, which gets its information from the fuel injector, is telling me that I'm getting 45mpg!) Based on the distance I had driven, it should take at least another 4 gallons at that point, no matter what!

Finally, the mechanic has now completely disassembled and reassembled the fuel tank assembly several times. He's swapped out the fuel tank. He's drained the fuel tank, and re-filled it, and then re-calibrated the fuel sensor. I've left the dealership with a full tank of gas, knowing it's a full tank of gas, and with strict instructions not to fill up until I have only 2 bars of gas remaining. Under those conditions, after I've driven close to 500 miles, the car should be accepting more than 4 gallons of gas at a time!