2001 Silverado. Gas tank implodes while driving then when I open the gas cap, it sucks a lot of air in and the tank goes back to normal. Gas tank also won't fill past 3/4 full. I've replaced the charcoal canister and the vent valve/solenoid. What else could it be?
Your fuel tank is going into a vacuum when the engine is running. The vacuum condition is causing the fuel tank to collapse and the gas cap is supposed to let in fresh air from the outside to keep the vacuum build up. I would recommend having the fuel tank checked to make sure it is not damaged and then check the fuel cap vent to see if it is stuck and gas cap needs replaced. Your fuel tank vent line to the carbon canister should be checked to make sure it is not pinched and flows freely to the carbon canister to the fuel tank.
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