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bwarner

Gas Tank Pressure

6 posts in this topic

Hi Folks...

This can't be good! If my '93 Lexus LS400 is almost out of gas, I get a big long gush of air coming out of the tank as I open the gas cap. I mean a lot of pressure is in there! As I open the cap slowly, it releases pressure slowly over 20 to 30 seconds. God forbid I open it fast and something sparks or there's a static electricity discharge! It would be a John Madden... boom! What could be the problem? Is there some vent or valve designed to prevent excess pressure in the tank that might be clogged? Somebody help me out before I become an ex-lexusownerclub memeber!

Brian

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The pressure build up is not due to faulty gasket but a faulty pressure control valve, as it does for controlling vapor pressure in a fuel tank that has an inlet line from the fuel tank, a pressure sensing line from the filler pipe, and an outlet line to a canister for handling the fuel vapor. Fuel vapor flow through the valve is controlled by ambient pressure from the filler pipe and tank pressure from the fuel tank, with those pressures acting on two diaphragms within the valve to alternately allow flow through the valve during normal vehicle operation and to prevent flow during refueling. A pressure relief valve is connected between the filler pipe line and the canister outlet line to prevent tank overpressurization should the valve malfunction.

The DTC tool would tell you exactly which is faulty. I cant remember the code off hand, but the tool should be able to tell you

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this wouldn't cause any engine problems would it? My car still has an engine light on for air to fuel rich and air to fuel lean.

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According to the manual this is perfectly normal ( mine does it as well and has caused no problems in 4 years).

It's not blowing air out of the tank but sucking air in, as the fuel is pumped from the tank it creates a vacuum and it's the air going into the tank when you release the filler cap.

Also proves the seal on the cap is OK.

Quote from the manual.

"It is not unusual to hear a slight swoosh when the cap is opened"

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i have same problem with my 94 ls 400 and the air is definitly comeing out not in. but i dont have any codesfor that but having a problem with car not starting like the fuel pump dont work. soemtimes it will start and run at as low idle and no matter how hard u hit the gas pedel the idle doesnt change. have to shut off car and restart it .. any ideas people im at a loss

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