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Fuel tank sucks in/expels air


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Recently reinstalled a charcoal canister from a glanza with working evap solonoid. refiled the car a few times when it was still cold without any noticeable issues. Today I removed to filler cap after driving for a few hours and I noticed it sucked in air. Any one knows if this is to be expected or should the canister be able to provide air to the gas tank. Will check the lines from and to the canister and probably replace them with some good fuel resistant ones of any damage is found.

Edited by RoyalDutchie
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Fuel tanks should be able to breath in and out, or vacuum is created when fuel is used or temperature decreases and as temp. increases pressure builds up in the tank.

Are you sure its vacuum and not pressure?

I know the systems are slightly different but I have attached a diagram detailing the corolla 92-97 4efe setup. Might be of some help to get the brain thinking or following hoses around the engine bay.

The TVV valve on the corolla (and starlet) is a coolant temperature dependant open / close valve situated on the thermostat housing. Is this replaced with a solenoid on the 4efte?

20200804_163845.jpg

Edited by Claymore
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Thx mate, the 4efte has an electric evap valve which connects the charcoal canister to the throttle body. Reinstalled it a about 6 weeks ago. Could have been pressure, but still shouldn't happen. Will check tomorrow when I arrive at work which of both it is. might be a case of a clogged filter😟.

Edited by RoyalDutchie
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Checked the charcoal canister today. when I removed the hose it blew out some air mixed with gas. So it seems like there is pressure inside  the gastank and line to the charcoal canister.

Also checked if the air hole underneath the charcoal canister both was able to release pressure and vacuum and it did both without any problems. so the canister breaths fine and doesn't seem to be clogged(checked if air came out of the connector to the fuel tank to check that one as well).  Connector on the charcoal canister to the fuel tank also didn't build any pressure when blowing through it, did take a bit of effort though(tested with a clean hose attached to it).

Edited by RoyalDutchie
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  • 3 weeks later...
  • 1 year later...
On 8/21/2020 at 8:27 PM, RoyalDutchie said:

Seems like the charcoal canister build a bit of pressure in the tank before the valve opens. This is expelled once the fuel cap is opened.

Sounds correct to me, I've done a bit of research into it and attached some pics from the 4efe UK owners manual for future reference:

20210915_072612.thumb.jpg.9cdb93861a496e9217a726ad4db6aa9d.jpg

The first diagram shows what happens with tank under vacuum / pressure and with engine running and at different engine temps. The starlet 4efe owners manual describes similar scenario. Looks like with the tank under vacuum air is led into the tank through the fuel filler cap check valve and no.3 canister check valve to prevent issues. With the tank under pressure the vapours are forced into the charcoal canister then led to the engine to be burned. (swoosh noise when opening the cap = small amount of pressure in tank).

Edited by Claymore
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