ok so i just did a lim gasket job on my dads car which has a l36 on first start up it smokes wich is normal as i had to burn off all the coolant it clears up and there is a slight missfire and i get p0301 so i replace the spark plug in cylender 1 problem gone i take it for a test drive like to the end of the block and back and it comes back with a p0301 and is missfireing again what is the problem