2012 jeep liberty

2 wd or 4 wd? tire pressure check,excess weight,slow down,
correct oil weight and viscosity,wheel alignment. 🙂

Did they check the fuel trims on the vehicle?

Also, Not pointing any fingers, but sometimes poor gas mileage is caused by the drivers right foot…..

-Karl

Fuel trims are what the computer adds or takes away fuel from the fuel injection… Most often expressed as LTFT (long term fuel trim) and STFT (short term fuel trim)… The computer makes adjustments based upon feedback from the O2 sensors and engine condition and readings from sensors… Most scanners give you this information… A high positve LTFT is adding more fuel than may be necessary (fuel trim can also be negative)… Ideally the LTFT should be 0% but on Toyotas (for example) they can be up to 20% before a code is thrown…. The higher the positive fuel trim, the more the fuel is being added and potentially using up unnecessary fuel..

There are other things that the computer takes into consideration that may be causing a rich condition (I.E. Intake Air Temperature sensor, Mass Airflow Sensor, coolant temp sensor)….

I would have this looked at on a scanner for any out of the ordinary readings… I think some Chrysler products have had issues in the past with running cold and not going into closed loop and constantly running in open loop because of the coolant temp, resulting in poor gas mileage)…

This dovetails into another issue… If your car is not going into closed loop and running longer in open loop, you are using more fuel than necessary because open loop is defaulted to be rich (to help the engine start when cold)…

-Karl

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If your code reader gives live data, then yes… If it just pulls codes… Nope…

HF has a fairly good one for around $80 with a coupon… I would suspect your vehicle may not be going into closed loop as soon as it should….

http://www.harborfreight.com/can-obd-ii-scan-tool-with-abs-60794.html

-Karl

What I am saying is that it could be using more fuel than it should… I would suspect it not going into closed loop (for whatever reason)… Sometimes when there is an issue with the coolant temperature (oftentimes caused by a partially open thermostat), the Coolant temperature sensor never reads the proper temperature to go into closed loop (because it requires the coolant temp to be at operating temp)….

Closed loop is where you get computer controlled fuel injection (thus the optimal amount of fuel/air mixture for the rated gas mileage)….. While in open loop (when engine is cold and all sensors say the car is not ready) the fuel mixture is defaulted to being rich…. When a car is stuck in open loop, it gets crappy gas mileage and may not throw a code.

I would hook up a scanner to the car when it is cold (first thing in morning) and monitor it as I drove it on my daily business, looking to see that the vehicle is going into closed loop)… If not going into closed loop, then the live data can give you a good idea of what may be going on (Based on the sensor readings) or if something is out of whack that can effect the mixture as well (I.E. Intake Air Temp Sensor says the temp is 40 degrees when it is actually 95 degrees)

-Karl