Nissan Frontier 2001 - gas filling problem
Is it possible for a charcoal canister to need replacing, yet it is not clogged,
or at least does not appear to be?
Here is the background:
I have a 2001 Nissan Frontier (3.3L). It's very hard to fill it with gas (and I am
not referring to the effect on my wallet). The gas pump shuts off after every
couple of pints of gas, as if the tank were full, and gas spills onto the floor.
But the tank is nowhere near full.
Looking on the web, Frontiers (and other Nissans) of the early 2000s seem
particularly susceptible to this type of problem.
Suspecting a blockage in the EVAP system, I disconnecting the vent
solenoid before filling the tank. This made no difference. Then I removed the
charcoal canister, blew through all the EVAP pipes (all clear, no
obstructions), and blew through the charcoal canister (again, no problem
blowing through it).
Finally, I returned to the gas station and tried again. First, I tried with all
EVAP components installed -- it was the same as before. Then I removed
the hose between the gas filler pipe and the EVAP canister, and I was able to
put more than a gallon in the tank before the gas pump shut off, and no gas
spilled on the floor. It's not perfect, but I could live with it.
Hence my question. When I removed the charcoal canister and did what I
have read to be the standard test (blow through it, testing for a blockage), it
tested out OK. Now I have to decide whether to buy a new charcoal canister
and see if that fixes the problem. Does my diagnosis (bad canister) seem
correct?
I forgot to add: the truck runs fine and the check engine light is NOT on. It's just that I can't fill the tank.
What happens if you blow back toward the tank? There could be a problem with the filler tube as well.
While the charcoal canister was disconnected, I blew into both pipes that lead to the canister, including the one from the filler tube to the canister. There was no obstruction.
If the vent is left open and you still can't fill the tank there is something strange going on. I can't think of any scenario where an open vented tank would not fill up normally.
The way the tank vents on your vehicle is this: (1) small vent tube in fill neck, if tank cannot be refilled even when nearly empty, look here. (2) there is a vent line from the tank to the charcoal canister. Then you have the charcoal canister with a filter in it (it can become gas soaked if you've overfilled the tank too many times). The canister "breathes" fresh air inlet line, that line has on it an EVAP canister filter and EVAP canister vent control valve. (That canister filter on the air inlet line is not the same as the charcoal filter.) So if the tank cannot relieve pressure caused by refueling, the problem most likely lies in the vent line, the EVAP canister or charcoal filter, or the Air inlet line with its filter and vent control valve. There is a pressure sensor inside the canister that governs the vent control valve on the air inlet. I would not worry about the purge valve or solenoid up by the engine, those wouldn't affect tank refueling problems. See pic below, to see how air needs to escape tank.
Thank you for the answers so far. Following up on KenF's answer: 1. Yes, it is difficult to fill the tank even when it is almost empty. So I will try to find the small vent tube in the fill neck and see whether it is obstructed. 2. I checked the three lines that are connected to the EVAP canister (tank to canister, air inlet to canister, and intake system to canister). All are unobstructed. In the case of the intake system line, I disconnected it at the purge volume control solenoid before testing the line. The car runs well, so I do not suspect a problem with the intake system. I wonder whether I perhaps have more than one problem. Disconnecting the line from the tank to the canister allows the tank to fill better, but the gas pump still shuts off every gallon or so. I think the possible contributors to the problem are: - The EVAP canister. - The small vent tube in the fill neck. - Perhaps the fill neck itself might be partially obstructed? Does that sound correct?
I would suspect the fill neck, but it's not easy to get to the vent built into it. You might also want to post this to a Nissan forum and see how common a problem this is.
I stripped it down to the gas tank and checked the vent tubes on the fill neck (two of them on this vehicle, it turns out), and the fill neck itself. Everything is clear. I've asked a similar question on a Nissan list but have not information so far. So it really all comes back to my original question. Is it possible that a charcoal canister that I can successfully blow through might nevertheless need to be replaced. I'll replace it in the next couple of days and report back here.
I should add that there are many threads in different discussion forums related to gas tank filling difficulties on Nissans of this age (2001) and throughout the 2000s. The problem affects Frontiers, Altimas, and other Nissan models. As far as I can tell, no one has a definitive solution. I wonder whether perhaps a new EVAP canister will improve things (as did disconnecting it) but not completely fix the problem. I'll report back here when I have the new canister.
