My Chevy Cavalier used one full tank of CNG perfectly, with no problems. When the CNG was empty, it automatically switched over to gas, but the console light on the dash was slow to switch, and blinked a red light to check guages or something like that. I drove on gas alone for 1000 + miles. The next time I filled the tank with CNG, the car drove about a block and then died. I got it started long enough to get the car off to the side of the road. It wouldn't start for 20 minutes. It started again, and I drove it a few blocks to a safer location, then I turned the car off and looked under the hood. It seemed overly hot under the hood.. I restarted it but it required me constantly pushing on the gas pedal to keep the fuel flowing. I drove it 70 miles on the freeway. As soon as I got off the freeway, it immediately died and would not restart for 20 minutes. I got it started again and drove it directly to a Chevrolet dealer service center. They kept it for 1 full day, it never died on them, and they said there was nothing wrong with it. We disconnected the CNG system so I could drive it on just gas because I didn't trust the CNG system. Drove it another 1000 + miles on just gas. Reconnected the CNG system, and have the same problem. It sputters or dies because of lack of CNG fuel making it to the engine. I have to rev the gas pedal constantly to keep the cng flowing. Does anyone have any insight on this problem. The Chevrolet Dealer is obviously incompetent.