Reduced Fuel economy no SES

[okfoz]

For some reason I have lost fuel economy, I keep detailed logs of mpg, date, temp for times just like this.

When I first got my 2007 Tahoe LTZ in 2014 getting 17/18 mpg in the summer, and 15/16 in the winter was never much of a problem. Now I am struggling to even get 15mpg it seems.

My driving habits have not changed, my work has not changed. I have a few ideas, my first was possibly a clogged Catalytic convertor, my dad thought maybe the O2 Sensors.

Anyone have any ideas. I know that the cold makes the MPG drop.

John

 

[CobraKing]

You'd probably get a CEL if it was a bad cat or O2 sensors. In all likelihood it's the gas stations switching to their 'winter' blends. Check your tire pressure too and make sure it's the recommended pressure.

 

[swathdiver]

Plugs wires and fluids? My mileage is not so great either but the motor runs like a top. Occasionally it'll throw a code for a bad cat but once cleared goes away for a while. Some folks say to change the upper O2 sensors every 100k whether they need it or not. I can only relate in that replacing the old 1 wire sensors did improve performance when we put fresh ones in.

 

[07 black beauty]

dont want to jinx but, is transmission slipping? Clean/ replace intake air filter.

 

[07 black beauty]

Have you found problem yet or, just going to live with it for now?