Hello, first post. My 91 4runner had a fuel tank leak, found tank bulged and a crack developed, weeping fuel. LONG STORY SHORT>>> found the evap system Charcoal canister TANK fitting internal checkvalve was stuck. Allowed pressure to build high enough to crack the tank! After two failed attempts to do a quick patch with epoxy I pulled the tank to repair/replace and while it was down went through the process of verifying the tank vent line from tank to canister was clear and no restriction. Next I tried to blow into the TANK fitting on charcoal canister and nothing. Hooked up air line to it and got up to 75psi before air started to flow. Read that 43psi is safe pressure to apply, check for your own safety etc before you try this. After that I tested blowing on it and air flowed ok with some vibration as the internal check valve operated. I did a lot of google searching on this, could have saved me a lot of time and trouble so I decided to post my experience. Hope this helps some one.

 

That is generally what happens when people over fill the gas tank. It fills the charcoal canister and problems ensue.

 

Old thread revival

So, of course there are other issues on the car, as I've only driven it about 20 miles since the rebuild of the engine and transmission. Of course I notice excessive pressure buildup in the gas tank.. why wouldn't there be another problem? lol...


I was looking at the FSM diagram for the system and from what I understand, and I need someone to confirm this, if the TVV valve is either broken I will have this situation? Also, the ports in the TVV valve are interchangeable, so it doesn't matter which hose goes to which port???

Right?

Thanks.

 

Excessive? Under common circumstances (warm day, tank only partially filled), the tank is under enough positive pressure to "whoosh" when you remove the cap. This is probably around single-digit psi. So how do you know your pressure is excessive?

According to the FSM, you can blow 43psi air into the tank pipe with the purge pipe closed in order to clean the Evap. In other words, you can't over-pressurize the tank even if your TVV is locked closed; air just releases from the lower vent in the evap.

The TVV is just a valve; the nipple connections can be reversed.

 

Well, from my experience gas tank releasing 2 seconds of pressure from the large filler cap sounds like a lot of pressure buildup.

Thanks for confirming the TVV valve operations... I have a feeling something with the charcoal canister is not operating properly. I also have read on the forum this kind of issue can manifest itself into various and multiple symptoms, atleast two of which I have at the moment (if my cylinder 1 is working)

I'm babbling now, but this all helps me think through everything!