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Fuel tank breather

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13 Mar 2025 18:15 #259788 by dpbenney@btinternet.com
Hello, 2002 Jimny, does the fuel tank have a breather or is it in the cap ?

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13 Mar 2025 18:45 #259789 by fordem
Replied by fordem on topic Fuel tank breather
The Jimny fuel tank like most is a "sealed system", as required by emission regulations.
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13 Mar 2025 19:56 #259790 by dpbenney@btinternet.com
Ok, we have what seems like fuel starvation on my lads Jimny, When I took her out the other day she took forever to get above 40mph getting close to 50mph she starts feeling really lean and then starts slowing down, been looking for an air leak but none found, she was plugged in for fault codes today nothing shown, thought I would loosen the fuel cap which made a difference, took the cap off altogether and she seems normal. The last test run fuel cap off we reached a mind bending 70mph. At a loss now, any suggestions gratefully received

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13 Mar 2025 22:11 - 13 Mar 2025 22:12 #259791 by DrRobin
Replied by DrRobin on topic Fuel tank breather
A petrol tank has to be able to breath or balance pressure, otherwise you couldn’t draw fuel from the tank.

My understanding is that positive pressure (caused by fuel expansion on a hot day or sloshing about) is vented through the EVAP canister.

What I am less clear on is how negative pressure (caused by drawing fuel) is dealt with. The standard way used to be to have a one way valve in the filler cap which lets air in as fuel is drawn, but won’t let fuel fumes out.

It could be that the Jimny uses the EVAP canister to balance the negative pressure caused by drawing fuel or has another mechanism, but it must have something.

2020 blue SZ5 (one of the last to be registered in the UK)
Ex 2011 Blue Jimny SZ4
Northumberland Jimny Blog

Last edit: 13 Mar 2025 22:12 by DrRobin.
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14 Mar 2025 07:11 - 14 Mar 2025 07:16 #259794 by yakuza
Replied by yakuza on topic Fuel tank breather
When going low on fuel the filler lets air in when I finally get to fill it.
When i unscrew the cap and there is a very distinct sucking sound from the filler.

Car never studders or anything though.

There is a small vent pipe coming up from the tank for letting air out when you fill petrol into it. 
it leads up to the cap I think and when your car goes fine without it, you might try to change the cap? or clean it and rinse out any valves if ther is any?

Well except when it actually runs out coming from the swedish forests where every station is closed or broken and when you get to Norway there is only Diesel :)

Norway 2005 Jimny M16A VVT, 235 BFG MT, 2" Trailmaster, ARB rear lck, 17%/87% high/low gears.
Last edit: 14 Mar 2025 07:16 by yakuza.
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14 Mar 2025 07:42 #259795 by yakuza
Replied by yakuza on topic Fuel tank breather
Just rembered there is a valve in line on the breather pipe /hose on my SJ. There might be one on the jimny too?

Norway 2005 Jimny M16A VVT, 235 BFG MT, 2" Trailmaster, ARB rear lck, 17%/87% high/low gears.
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