1997 Oldsmobile Bravada Q&A

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

the gas tank looks like its collapsing in on itself. -
Answer 1
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 2
Should have evap trouble codes, is the check engine light on? Vacuum when removing gas cap and does the tank pop back out? -
Comment 1
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. -
Answer 3
did you just install a new gas cap? or ck #1 suggestion and scan evap codes -