I was getting 16-18 mpg and then suddenly I've been getting 11mpg out of nowhere. Any ideas? No check engine lights or anything. It's also been burning through oil so not sure if that's related. 4.0 97 on 31s with a one inch lift.
Did you notice any particular occurrence (no matter how minor) that might indicated something that caused the MPG drop ?
I would pull the spark plugs to identify which cylinder is burning the oil.
Have you noticed a rough idle, misfire condition or a low engine temperature ?
Has the engine idle RPMs changed any ?
Take a look at the O2 sensor wiring to see if something happened to them; paying special attention to the upstream sensor.
Has your catalytic converter been replaced?
When the gas mileage dropped off; was there a noticeable drop in power and acceleration ?
That could be indications of a catalytic converter being obstructed.