Burning smell coming out from 2005 Ford Explorer?

My truck has been sitting in a drive way for 2 years recently I changed the battery and filtered the fuel and now something smells like its burning is it just the old fuel or something else that could be making the smell?

Could be residual. Could be the valve cover gasket has dried and is leaking. Could go away, could get worse if that gasket has now cracks. Specific source if leaking, could be from a different location as this is just an educated *typical* source guess. As we can't inspect from this remove. Keep tabs on all fluids and gages. Persists, see a trusted/qualified mechanic/shop.

Did you get the battery installed right? Yes, start the vehicle and check for smoke. Have a fire extinguisher ready.

I mean.there's a fire inside the engine. So it should smell like it's burnin.haha.

If it's not engine related (worn out piston rings, usually… Aka switch to a higher viscosity oil.) then it's your catalytic converter failing… Or it could just be some leaves, spider webs, bugs, mice, snakes, etc that got somewhere in there.

Sitting in the driveway for 2 years? Besides visible mouse nests on the engine, they can be in the air cleaner & tubes, around exhaust manifolds and pipes, could have entered the tailpipe and nested in muffler, converter - right up and into the engine, around the radiator… Virtually anywhere with a 1/2" opening. If the engine is running, the heat is going to clear-out any infestation soon. Just hope that none made it into the upholstery, under carpet, heater/defroster ducts, headliner, etc.