We had about a gallon of old gas (probably from the lawnmower) in a container and were trying to find somewhere to dispose of it (not easy). Someone suggested to simply add it to our vehicle's gas tank, which is what we did. Alas, the next day, the truck (2000 Ford F150) wouldn't start--that was almost a week ago. Our mechanic has been trying to diagnose it but no luck so far. At first he thought we'd need to replace the fuel pump, but since there is pressure in the pump, it seems that's not the problem. We added gas treatment and the temperature has been regularly well above freezing, so ice in the gas tank also isn't the problem. Help!