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Jeep Wrangler YJ
YJ General Discussion
Oil In The Fuel Tank
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<blockquote data-quote="Gary747" data-source="post: 428969" data-attributes="member: 19207"><p>My YJ is the 1990 version, converted to fuel injection (got rid of the carburetor) and I have observed something that I ask others to comment on. Whenever I open the gas cap to refuel, I experience tank pressure relief as the cap loosens... the tank is pressurized as I drive. The lower the fuel level, the more pressurized "air" volume in the tank and the bigger the "hiss" is as the cap comes loose. I've always liked this, as this pressurized fuel lessens the work required from the fuel pump to move gasoline to the injector rail. I've already been challenged that it's really a vacuum and that I am misinterpreting the direction of pressure relief. BUT, I can guarantee that the tank is pressurized and that the relief airflow blows OUT of the gas filler port.</p><p></p><p>I have always felt that the pressure comes back to the fuel tank from the charcoal filled evap canister in the emissions system, but I'm not positive. But since this thread concerns oil or other contamination getting into the fuel tank, I can definitely say that on my Jeep, there is a positive energized flow conduit INTO the fuel tank. So my recommendation is to think about this when tearing into your tank, that there may be an unfiltered by-pass in your fuel pump or emissions system allowing contamination to enter. If your tank no longer holds pressure (vacuum or positive), consider loose filler hose clamps and an open (broken) rollover anti-leak valve (located behind the right rear wheel well on my Jeep).</p><p></p><p>Please, though, remember to post what you find... many come here looking for advice but we often don't hear how it comes out. These unusual problems are a pain for you, but a learning opportunity for everyone.</p></blockquote><p></p>
[QUOTE="Gary747, post: 428969, member: 19207"] My YJ is the 1990 version, converted to fuel injection (got rid of the carburetor) and I have observed something that I ask others to comment on. Whenever I open the gas cap to refuel, I experience tank pressure relief as the cap loosens... the tank is pressurized as I drive. The lower the fuel level, the more pressurized "air" volume in the tank and the bigger the "hiss" is as the cap comes loose. I've always liked this, as this pressurized fuel lessens the work required from the fuel pump to move gasoline to the injector rail. I've already been challenged that it's really a vacuum and that I am misinterpreting the direction of pressure relief. BUT, I can guarantee that the tank is pressurized and that the relief airflow blows OUT of the gas filler port. I have always felt that the pressure comes back to the fuel tank from the charcoal filled evap canister in the emissions system, but I'm not positive. But since this thread concerns oil or other contamination getting into the fuel tank, I can definitely say that on my Jeep, there is a positive energized flow conduit INTO the fuel tank. So my recommendation is to think about this when tearing into your tank, that there may be an unfiltered by-pass in your fuel pump or emissions system allowing contamination to enter. If your tank no longer holds pressure (vacuum or positive), consider loose filler hose clamps and an open (broken) rollover anti-leak valve (located behind the right rear wheel well on my Jeep). Please, though, remember to post what you find... many come here looking for advice but we often don't hear how it comes out. These unusual problems are a pain for you, but a learning opportunity for everyone. [/QUOTE]
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Jeep Wrangler YJ
YJ General Discussion
Oil In The Fuel Tank
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