what is causing the bottom of the gas tank to suck inward? on 1997 Oldsmobile Bravada

the gas tank looks like its collapsing in on itself.

by in Lafayette, IN on February 20, 2013
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3 answers 1 comment
ANSWER by , February 21, 2013
did you just install a new gas cap? or ck #1 suggestion and scan evap codes
ANSWER by , February 20, 2013
I have seen both vent valve failures and canisters saturated cause the same thing.The purge valve pulls a vacuum on the tank at a predetermined time and after it's done the vent valve will release the vacuum from the tank,yours is not releasing this vacuum.
ANSWER by , February 20, 2013
Should have evap trouble codes, is the check engine light on? Vacuum when removing gas cap and does the tank pop back out?
COMMENT by , February 21, 2013
its not giving a code, I replace the gas cap awhile ago. I replace the gas tank since the bottom had collapse {it was like half a tank} but the problem has came back, the bottom of the tank has sucked up about 1/2" and will not pop back. I had a friend put his computer on it and where it says evap cycle it just says NO.