Fuel tank breather , how does it work ? sj410 1986

[SteveR]

hi all

My fuel tank is always under vacuum with engine running and holds a vacuum when stopped.
Guess this is wrong and breather blocked somewhere, but where and how does the breather work, is it in the locking fuel cap ? If so how does it work and best way to clean it .
Is there a tube somewhere under the body but I can't see one.

Thanks
Steve

[Jordi]

There is a steel pipe approx 10mm thick on the top of the tank. This has a rubber / plastic pipe that runs up through the floor and connect to the filler neck just inside the wing.

Inside the back of the SJ there is an access panel that unscrews, literally the inside of where the filler cap is.

[Rhinoman]

You should be able to see a breather hole on the underside of the cap, usually they vent through the keyhole.

[SteveR]

thanks jordi and rhinoman

Yes can see tube in filler neck so to vent to outside must be through filler cap, please see photos and explain how.
blowing through key hole air does come out of two larger holes on underside but as can see in photos when cap is on car with rubber seal those holes are effectivley on the outside of filler not inside. The two small holes on " body " of cap do not seem connect to outside, I have tried cleaning by boiling in water for 5 mins so should all be cleear inside.
The cap is the original with SJ stamped on it.
any ideas or could someone please photo inside of their filler cap with seal on and off for comparison.

thanks
steve

[SteveR]

Too answer my own question, may helpful to others.
Found a diagram on internet, there is a second tube connected in filler neck on top side , this tube is the breather and goes back down under bodywork behind rear bumper, by torch light tonight have found tube, hopefully tomorrow will find it blocked under bumper and prob solved , will let you know.

so on a sj 410 does not breath through filler cap but out under rear bumper, for those that go deep wading maybe a one way valve would be a good idea.

Steve

[Rhinoman]

I have a vague recollection of a small orange valve on that pipe. My cap may well be an aftermarket item.

[Darrell]

I can often hear a vacuum when removing the filler cap, it's never been a problem as it runs fine.
I assume this is caused by the one way valve as it may have a spring to close the valve.
This being the case it will require a low vacuum before the valve would open to allow air in.
Well that my take on it ..

[Tramp]

Your correct Darrell mine was exactly the same, it always used to 'suck' when removing the filler, I thought my orange one way valve was buggered so changed it for a little inline fuel filter, did it make a difference? Well it stopped the sucking noise but didn't effect the running at all, I've been meaning to refit my valve for a while now!

[SteveR]

Quick update.

Checked this morning, found breather tube behind rear number plate, blowing through tube with bit of force all is clear, there is a valve in there somewhere as needs a little force, sucking on tube closes valve. So outcome is that it is normal for there to be a little vacuum in the tank, a spring valve regulates the amount of vacuum and stops the possibility of water entering.

So changes nothing but I'm happy now knowing it's normal.

Thanks for the info and diagrams guys.

Steve