Started having gas mileage issues mid November, had mid muffler delete done beginning off December. Gas mileage has gotten worse since.. now I’ve got a layer of black soot on the rear end of the car. Bad gas mileage as in I went through half a tank in 40 miles. Didn’t have my foot in it either, city driving.
I’m an advisor at a dodge dealership, master tech looked it over and everything was “in spec”
don’t think he has any interest in actually tearing into it.. service manager says muffler delete voided my warranty. Everything I’ve read online says I didn’t. Just not sure where to go from here. Talked to the place that removed mufflers and a few other shops, all think I have a leaking injector or bad o2 sensors. No cel, normal performance while starting and driving.

 

They can't void your warranty unless they can actually prove that caused your problem (Magnuson Moss Warranty Act). Is it running the stock tune?

 

How many miles on it? Done any other work to the drivetrain?