FZJ105 Fuel tank breather for negative pressure location?
Submitted: Thursday, Dec 21, 2023 at 12:35
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Spasticbadger
Hi everyone, first post!
I have a 2002 FZJ105 which I’ve had for a year now, I love it, she’s a bit thirsty but that’s a small price to pay.
Ever since buying the car when I go to refuel air is sucked INTO the tank when I remove the filler cap. It’s got to the point now where if I’m going for more than half a tank without stopping the car will stall when coming off throttle and I have to get out and relieve the pressure by removing the cap.
I replaced the fuel cap in case it was faulty but no difference, as far as I can see the fuel cap allows excessive pressure out but not in as it’s a one way valve. This has led me to assume there is a second breather/valve for replacing the fuel used by the engine with air from outside. The question is where is it?
I’m really struggling to find info on this and any input would be greatly appreciated.
The car has the stock 90L tank and LPG conversion (which I haven’t used).
Thanks.
Reply By: Member - LeighW - Thursday, Dec 21, 2023 at 13:22
Thursday, Dec 21, 2023 at 13:22
Had a look at amanya for you, it would seem the breather is attached by a short tube. As such I would look at the top of the fuel tank as it must be pretty close to the tank if not on it.
AnswerID:
644944
Follow Up By: Spasticbadger - Thursday, Dec 21, 2023 at 15:36
Thursday, Dec 21, 2023 at 15:36
If possible could I please get a link or screenshot of what you are referring to? Thank you
FollowupID:
925156
Reply By: RMD - Thursday, Dec 21, 2023 at 14:55
Thursday, Dec 21, 2023 at 14:55
In what way was the tank cap faulty? Most filler caps allow air to enter to reduce the negative pressure from fuel usage. The replacement is faulty too if still happening and is the cause. My little Corolla also breathes in when removing cap. Entirely normal to have some negative woosh when removing cap.
I would be thinking the fuel pump isn't drawing sufficient flow against the vacuum which builds up. The rotor cell in the pump may be issue OR the pump is running slow and cannot overcome the normal neg pressure of the cap valve. What voltage are you getting AT the pump terminals? They must spin fast to get the job done. Look past the cap is my thought.
In modern fuel systems the tank doesn't allow fumes to atmosphere, Pollution rules!
AnswerID:
644945
Follow Up By: Spasticbadger - Thursday, Dec 21, 2023 at 15:43
Thursday, Dec 21, 2023 at 15:43
I don’t think it was but it was $12 from repco and worth throwing at it before I have to go underneath and go finding pipes/dropping fuel tanks. The cap has a one way valve in it, I can blow through but not suck through it, hence my suspicion there’s another breather somewhere. It’s a massive long, loud whoosh if I leave it tight and remove after a decent drive, definitely not something I would consider normal for any car.
The fuel pump is definitely on the cards as
well but if I leave the cap loose it drives perfectly through a full tank hence me leaning towards a blocked breather at the moment.
FollowupID:
925157
Follow Up By: Bob Y. - Qld - Thursday, Dec 21, 2023 at 18:00
Thursday, Dec 21, 2023 at 18:00
The other breather should be on the passenger side front of the main tank. It is a white nylon thingy, about 25mm in diameter, flat on one end & tapered on the other end. There is a barb on each end. On one end there is a short rubber hose that plugs into a fitting on the chassis. If it’s had a hard life, the rubber hose may no longer be hooked onto the chassis. The opposite end should be hooked onto something on top of the tank.
Get replacements at Toyota, should only be a few bucks?
Bob
FollowupID:
925158
Follow Up By: RMD - Thursday, Dec 21, 2023 at 18:36
Thursday, Dec 21, 2023 at 18:36
SB
Is the massive long woosh, inward, ie vacuum or exhaling.
If you can blow through it, which way are you passing wind?
ie, into the tank or out of the tank? You didn't say which way!
If you can pass air with mouth pressure from outside to inside, then there isn't much pressure difference with mouth pressure, nothing significant.
If there is a "breather" and it breathes the tank pressure/vacuum, there won't be ANY vacuum or pressure in the tank.
FollowupID:
925159
Follow Up By: Spasticbadger - Thursday, Dec 21, 2023 at 21:22
Thursday, Dec 21, 2023 at 21:22
RMD: It’s sucking air into the fuel tank (vacuum), if I try and suck through the underside of the fuel cap I can’t. The valve is a one way valve you can see it work when I blow through it (with minimal pressure). The one I replaced works exactly the same. I’m worried it will end up collapsing the fuel tank.
Bob: I’ve had a look under the car, there are two locations that things come out, firstly the fuel pump so send/return lines etc and the other is an electrical connection on the P/S top that I presume is the fuel level sensor. I’ve had a look at identical tanks for sale on eBay etc and cannot see any other connections, I also can’t see anything that you’re referring to on the technical parts diagrams… Maybe I’m being stupid :(
FollowupID:
925161
Reply By: Member - Rob S (NSW) - Tuesday, Dec 26, 2023 at 10:10
Tuesday, Dec 26, 2023 at 10:10
Hi
At guess your 105 fz will be much the same set up as my 95 fz 80 series?
The usual cause for excess vacume in the fuel tank is your charcoal canister under the bonnet is cactus.
Very common with fz 80 series with the age of them, the ball valves in side eventually rust up and they don't breath how they are supposed to,
the canister is a black steel container (could be plastic in a 105?) under the bonnet it collects fuel vapor from the fuel tank, when then engine is started , a valve opens on the inlet manifold for 3 seconds and draws the stored fuel vapor into the inlet manifold.
easy to
test once you find the charcoal canister, should have 2 hoses on it ,one to the manifold and one to tank usually marked on the canister, slip of the tank line and let it breath to atmosphere , try this and it should solve your problem.
if that fixes it? you need a new charcoal canister ,but they aren't cheap.
Or you can just delete it, block the hose to the inlet manifold, put a cheap plastic inline fuel filter on the tank breather hose to stop crap going back ,and extend the hose down into the chassis , or you will get fuel vapor smell in the cab , and you may notice a fuel vapor smell on hot days with a full tank of fuel, i haven't really found any issues with letting the tank breath to atmosphere. though as RMD said they are not meant to breath to atmosphere , pollution rules etc, easy enough to plumb it to look standard .
Cheers Rob
AnswerID:
644971
Follow Up By: RMD - Tuesday, Dec 26, 2023 at 17:13
Tuesday, Dec 26, 2023 at 17:13
It seems to be a vacuum problem, ie runs ok with cap off. However, a vapour canister if the valves are rusted would have to be stopping air from traveling down the vapour breathe out line during normal use. If not there would be vapour pressure in the tank when warmed. That means the air has to be drawn from somewhere. So, the valve which allows fumes to be drawn into the manifold on startup MUST be a two way valve and have a breather on it to allow air in and to the tank when running. The valve mentioned IF faulty would possibly also be stopping fumes from tank to canister. Might be two problems there.
FollowupID:
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Follow Up By: Spasticbadger - Sunday, Dec 31, 2023 at 22:51
Sunday, Dec 31, 2023 at 22:51
RMD, I’ve checked out the charcoal canister and I can blow/suck down the feed/returns lines so no blockages/stuck valves. I’m starting to think it’s the fuel caps Repco sell, they’re only $12, a proper Toyota one is 80. There’s a valve in the cap, there’s no way that’s to let anything out of the tank as it would be petrol fumes, so by deduction it must be to let air into the tank, there’s no reason for that to be run through the CC as long as it’s through some sort of mesh filter like most fuel caps, it just needs to be air. I’m going to get my hands on a proper Toyota cap and see if that works.
FollowupID:
925232
Reply By: Member - Northern Wanderer - Sunday, Dec 31, 2023 at 21:06