Gas Mileage Dropping Suddenly

Bobohunter1776

TJ Enthusiast
Supporting Member
Joined
Jun 20, 2022
Messages
758
Location
Evergreen, Colorado, USA
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.
 
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.

It definitely has a pretty rough idle but it's been like that since I bought it and I think may have gotten worse but not a 100% sure. The idle rpm hasn't changed at all.
 
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.

Nothing noticable. There is a hole in the exhaust just before the cat so I'm not sure if that might play a role in it. When I get I chance I'll check the O2 sensors and converter.