Well today I cut my muffler off becuase the bottom is practically rusted through, i belive it the stock muffler, has dodge emblem on the underside. Could a plugged up muffler cause my fuel milage to go down. I noticed driving with a straight pipe right now, its actually somewhat better, only put 200km on since the muffler was off, and I dont mind the sound it makes either haha, kinda like a blender muaha..

Could this be possible the muffler caused it to get poor milage?

 

Absolutely, and actually my family had a Dodge 1-ton van that had the baffle plates slide together and it ran like crap. Messed it up fierce. However being a 360 HD in a 1-Ton it got 10 MPG no matter what. Uphill, downhill, loaded, unloaded, AC on or off and any combination you can think of. Being in tune just meant better accelration and you could squeal the tires from a standing start without brake torqueing. But a 4 Cylinder sure a bad muffler can ruin performance without a doubt.

 

yup change it
..

 

How many miles are on the car. The cat might be plugged too.