my car will not start, it back fires some while i turn it over, it has spark com on 2003 Buick Park Avenue

no codes come up has spark & compression seem s to be flooding out, was running perfect,did it jump timming? Just will not start..

Asked by for the 2003 Buick Park Avenue
1-Very possible your gas has water or other contaminants in it. 2-Also possible the crankshaft sensor behind the harmonic balancer is failing.
Mechanic needed to check it out hands on!! It has NOT jumped time. That just don't happen on this engine! Are you pretty car engine savvy?
sometimes not too savvy on trouble shooting, car has plenty of spark,also compression,car has been sitting for 3-4months with about half tank of gas, I started it last week, had alittle skip came out of it, let it runn for half hour then stepped on it couple times, lost its power then shut down, havent got it started since, pugs get wet but come to think of it they dont smell very strong gas smell, you could be right maybe the gas went bad from sitting, all i know is it ran like a top several months ago, and now don't, what do ya think now that i gave you more info?
Have you added any gas from a can? Any gas been added while it was parked? If it was out of time, compression should be low!
no I have not if it is bad gas shouldn't I drain tank?
Fuel sample needed. For a mechanic to check.