Thanks. Another update. Not content to leave well enough alone (or to wait for several successful re-fills), I found a thread mentioning a TSB for a different model/year Explorer. It mentioned a problem with water gettng into to vent hose because of a failed connection between the hose and the fuel filler housing. I know that this was not my problem, but bear with me a bit here . . . .
Evidently water is bad karma for vapor canisters and other evap system parts. The TSB mentions checking the fuel for water. I don't remember exactly why, but I do recall a few months ago dumping two cans of alcohol/water absorber into the gas tank. I've run lots of tankfuls of gas since then, and even ran the tank down to 0 (in line for the pump at Costco; another guy helped me push the truck up to the pump!)--so I know I don't have water in my gas. (If it matters, I have the Flex fuel engine K.)
Another part of the TSB caught my eye. It said if that there is any water in the tank, replace the evap purge solenoid. Then I thought about it. When that solenoid duty cycles on, it pulls a strong vacuum through the evap line--into the intake manifold. If there is any water in a canister or line (or water vapor)--it would get sucked right through the purge solenoid.
On the test drive I mentioned above (before the successful fill), I monitored the fuel tank pressure sensor (volts) and tank pressure (inches of mercury). The tank was about 3/4 full. I wondered if I might have a bad sensor (not sure why). Anyway, it was jumping pretty wildly, every second or so. Tank pressure was between 0.70 down to -(negative) 10.0 inches. Seemed wild to me, but maybe PCM was doing a evap test. I don't know what normal readings are, though the tank's normal pressure range is supposed to be, but the sensor's normal (KOEO) control volts are supposed to be around 2.69 volts.
Anyway, I had a spare purge solenoid from a donor, lower-mileage truck with no mouse chewing history, so I pulled it and went to swap it last night. I had a heck of a time pulling the upper hose (which runs to the intake, when the valve cycles open) off the old purge valve. Once I did, I saw it was crusted with white powder around the inside where it connected to the old valve. And when I tipped the valve down, white powder/crud sprinkled out of the corresponding port!
Monitoring the fuel tank sensor/tank pressure this afternoon (with full tank) shows a lot less jumping around. Not sure whether that's b/c of the full tank or the new(er) valve, or both. My working theory, however, is that during the time (couple thousand miles) that the evap hose connecting the rear and front charcoal canisters was chewed open by mice, the purge valve, when duty cycled on by PCM, would suck air through that large hole. If it was raining or even damp out, that introduced water into the purge valve, and likely crudded it up, compromising performance.
Anyway, I thought I'd report this in case this had something to do with my gas tank filling problem. If the old purge valve was working only partially, it might not have fully evacuated the canisters of gas vapor or removing pressure from the tank. This might have left canisters more likely to block air flow out of the top of the tank --causing gas fill problems.
