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Not plugged or pinched hoses

A vacuum seems to pull the metal of the 1999 gas tank, then when shut off, a “ping” sound occurs within 5 minutes. The sound supposedly comes from the tank resuming the original shape. This didn’t happen before removing the gas tank to replace the fuel pump. Does the gas cap have any venting system? Any suggestions will be appreciated. Thanks!

Because of the emission standards today, you should have sealed cap and the fumes goes to a charcoal cannister. Sounds like you might have a restricted hose to the cannister. Maybe pinched when tank was reinstalled.

Most gas caps let air in but not out to comply with emissions standards. Replace the gas cap. You are overworking your fuel pump if the gas tank has a vacuum.

Thanks Hiroshi and Missleman
I’m wondering if someone out there knows if my 99 suburban gascap is in the category of “most” and actually lets in air. or does anyone know where i can find that info. Thanks again.

The gas caps for your vehicle are the pressure relief/vented type. That means in lets in air. If your tank is “buckling” due to vacuum then the gas cap is bad. Check out this website:

Missileman may be right about the gas cap allowing inward venting, but even of that’s the case the tank should be able to breath in through the charcoal bed in the charcoal canister. I’d still check the canister out.

Are you getting a CEL light?

No CEL and I’ll check the charcoal canister. Thanks to everyone. I won’t be able to reply for a couple of months because of extended vacation.