2000 Ford F 150 Had F 150 Parked 6 Months After Months Tried Start Back Battery

i had my 2000 ford f 150 parked for 6 months. after 6 months i tried to start it back and the battery was death, so i gave it a jump with some wires from another truck. the truck started normally but the battery wasn't holding charge. i gave it a jump for 3 times. and the 3rd time i started, it started very rare it almost got off by itself and some white smog was coming out of the exhaust. i went to a gas station and put some more gas and i stayed the same. so i toke it to a mechanic. they said that the old gas was causing the problem so they drop the gas tank down and cleaned it and put some premium gas on it and nothing happened it stayed the same. they put new spark plugs and it stayed the same. they cleaned the fuel injectors and the same. and every time more and more smog. the 2nd day we notice that the oil was half quart low and they replace a valve and the same. they have been trying to with a scanner and it gives no code. and the ( service engine) light is not on, very rare because you can feel the vibration on the car and a big cloud of smog. i need help.