Is gas tank supposed to suck or blow when you remove gas cap?

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FJ62Landcruiser

FJ62Landcruiser

10 Year
Joined
Aug 15, 2011
Threads
20
Messages
64
Location
Oriental, NC
1989 FJ62 FEI

When I got my cruiser it came with one of those aftermarket locking gas caps that was loose fitting and annoying to remove.

I recently got an OEM gas cap from the local Toyotal dealer.

I've noticed with the new OEM gas cap that when I remove it to refuel there is a lot of air pressure released that was built up in the tank.

Is this normal?

It really blows out hard for a couple of seconds.

When removing the gas cap after running is air supposed to blow out from being pressurized or suck in from a vaccuum?

Thank You,

Rod
Oriental, NC
 
The charcoal canister and related hoses, valve, etc need looked at. The approx 6" diameter canister is located under the hood on the passenger's side low down and about a foot from the firewall. refer to the fsm on how to check it.
 
Coyote is right; you have a charcoal canister and/or related plumbing issue. When everything works correctly, there should be little pressure disparity between the tank and the atmosphere. If anything, a small amount of positive pressure in the tank is normal.
 
Has it had the fuel tank recall? My original tank was also audibly exchanging pressure with the atmosphere every time I removed the gas cap, but since getting a new tank in 2009 it does not. I believe excessive pressure build up was in fact the reason for the recall.
 
Thanks for the heads up, my gas cap releases pressure every time I remove it.
 
you certainly want the tank to vent...you don't want there to be a negative pressure area in the tank where the fuel system fights the thank to pump fuel and you don't want to be really pressurizing the tank...where you go "boom"....

I think the only place to buy those charcoal canisters is Dealer if they even offer them or used. A lot of emissions stuff is dealer only. I would certainly hunt down at shop manual to test the fuel evap system...

If you have to meet emissions then the charcoal cannister is mandetory I suspect.

My truck when stock use to be bad about the tank pressurizing ...you could hear the hiss when you opened the tank...

Since I've completed my engine swap and I don't have to meet emissions laws here my fuel tank vent line that use to run to the charcoal canister now just vents to atmosphere. I have a long piece of fuel hose that attaches to the hard line at the firewall and runs over to the drivers side fenderwell and is just open on the end. No raw fuel, no gas smell. no more pressurized fuel tank.
 
I've had three 60's and one I bought new from the dealer and they all burped a little when opening the gas cap. However the gusshing he is describing seems excessive and the canister is a good place to start to see if there is a problem. :)
 
Blow. Giggity.

I can't explain exactly how the evap and fuel pressure return systems work (in detail anyhoo), but 62's are supposed to have pressurized fuel tanks.

Someone correct me if I'm wrong, but all EFI systems with a properly functioning fuel/fuel vapor return will have a pressurized tank.
 
maybe a better expression on my part is controlled pressure and or vacuum.
 
Spook50 said:
Blow. Giggity.

I can't explain exactly how the evap and fuel pressure return systems work (in detail anyhoo), but 62's are supposed to have pressurized fuel tanks.

Someone correct me if I'm wrong, but all EFI systems with a properly functioning fuel/fuel vapor return will have a pressurized tank.
Click to expand...

I have no supporting data, except that I have a sticker near the fuel filler that says to remove cap slowly as it is pressurized. Mine does a slight hiss at removal of cap. New tank.
 
89GASHOG said:
Has it had the fuel tank recall? My original tank was also audibly exchanging pressure with the atmosphere every time I removed the gas cap, but since getting a new tank in 2009 it does not. I believe excessive pressure build up was in fact the reason for the recall.
Click to expand...

Yes...it has had the replacement tank from the recall some time ago.

This morning I switched the two hoses coming off of the top of the charcoal cannister prior to running some errands and refueling.

When refueling I closely noted the pressure as I removed the gas cap.

There was no pressure...or if there was it was unnoticeable.

That tells us that the check valve in the charcoal cannister has malfunctioned.

I didn't notice any fuel odors running it like this so I may just leave it like this.

If I begin to notice fuel odors I'll order a VC120 charcoal cannister from AutoZone (pictured below). They're only $38.00 vs. $300.00 for an OEM which may or may not still be available. I found that a lot of the FJ80 guys are running those VC120 CC's with good luck.

Thanks a lot for everyone's help in diagnosing this.

Thanks Again,

Rod
Oriental, NC
cc.webp
 
Spook50 said:
Blow. Giggity.

I can't explain exactly how the evap and fuel pressure return systems work (in detail anyhoo), but 62's are supposed to have pressurized fuel tanks.

Someone correct me if I'm wrong, but all EFI systems with a properly functioning fuel/fuel vapor return will have a pressurized tank.
Click to expand...

I agree. My 89 has burped since I bought it in 93. It always passed emissions until I moved it to a non-emissions county. I think the reason for the fuel tank recall was there were tanks that were not holding the pressure but instead leaking gas or fumes at seams. If pressure in the system was a problem Toyota would have been working on reducing the pressure as well as replacing the tanks. The whole purpose of the sealed system is to keep gas fumes in not keep air out. It would makes sense the charcoal canister has design flow rate to work properly so some pressure would be normal. How many times do we open our gas caps other then to fill the tank. To fill the tank we drive to a gas station shut engine off and open the tank. I guess a good check would be to open the gas cap when the engine hasn't been run for hours. It would seem the pressure would be relieved thru the charcoal canister. If it doesn't then remove the inlet hose from the canister and see what happens. If you hear a pressure release then I would say the canister is plugged and needs to be replaced. As for the pressure getting to high the pump can only do a certain PSI and that is the most any part of the system can see. I would think Toyota designed the whole system to handle that pressure.
 
Every time I see the title of this thread, I can't help thinking of Monica Lewinsky...
 
Every car/truck I've ever owned has released a little pressure when removing the gas cap. Especially if low on fuel. My 62 releases a little pressure when I remove cap but nothing alarming.
 
I switched the lines on my 1983 FJ60 nine years ago, heeding some advice from the LCML. Wow, it's been awhile. No ill effects since.
 
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