I had this problem on a Chevy Impala with the 3.8 V-6. The fuel would be forced back out of the filler neck, and the gas pump would keep shutting off when I tried putting gas into it. I started the engine, and would fill the tank with the engine running to get rid of the problem. That led me to believe the problem was in the EVAP system. That car also had an oxygen sensor, and a mass air flow sensor go on it, and the check engine light did not come on. The dealer said the check engine light should have come on when these parts failed. The failed sensors ended up ruining the catalytic convertor, and that also had to be replaced. After replacing the converter, the check engine light finally came on, and the system had to be reset. I ended up getting rid of that car.
I had this problem on a Chevy Impala with the 3.8 V-6. The fuel would be forced back out of the filler neck, and the gas pump would keep shutting off when I tried putting gas into it. I started the engine, and would fill the tank with the engine running to get rid of the problem. That led me to believe the problem was in the EVAP system. That car also had an oxygen sensor, and a mass air flow sensor go on it, and the check engine light did not come on. The dealer said the check engine light should have come on when these parts failed. The failed sensors ended up ruining the catalytic convertor, and that also had to be replaced. After replacing the converter, the check engine light finally came on, and the system had to be reset. I ended up getting rid of that car.