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97 chevy lumina

I have 30k on my 97 Chevy Lumina. there is so much vacuum in the gas tank that it crushed the tank. I have replaced the tank but don’t know what the problem is. Have taken it to three different shops and got three different opinions. One shop replaced the purge solenoid, no luck. Another said there is no fuel tank pressure data and want to drop the tank and check the sensor. the error code they read is p0440. The other replaced the evap canister. Am driving without the gas cap to protect new tank.I don’t want to pay for another unnecessary repair and am sure I can repair it myself but want to be cartain I have it right. Also I didn’t realize there was a pressure sensor in the tank. They also said I could have a restricted vent valve or canister.

Your gas cap should have a one-way valve to allow air into the tank as gas is used, to prevent a vacuum from forming. If your tank is being crushed by a vacuum, that means the gas cap is not venting correctly. Has anybody bothered to check the gas cap??

Also, it’s possible someone installed an incorrect non-vented gas cap, which would also cause the vacuum.

Try buying a new (vented) gas cap for $25 before spending any more $$ on mechanics.

I’ve seen this a few times. The solution was a new gas cap. If the gas cap vent is damaged or doesn’t operate then the fuel pump will pull both air and fuel out of the tank. When this happens…the gas tank collapses.

I forgot to mention that the gas cap is the first thing I replaced.

I just checked, and the OEM gas cap is an AC Delco GT279 cap which is apparently unvented. So the gas tank must be designed with a vent somewhere else, that is apparently not working.

I’d try to find a replacement cap which is vented, and this should solve the vacuum problem. I just searched autoparts for your car and they have several Stant caps which are vented that will fit your car.