Declining Gas Mileage in 1996 Yukon

[ryankbruce]

I have a 1996 Yukon that I am having gas mileage issues with.

The normal performance had been 14mpg or so in the city and around 16mpg on the highway. I have 225000 miles on the vehicle.

The first decline was due to the oxygen sensor going bad and I had the computer flashed to enhance the performance of the valve that the sensor controls. Once this was replaced, the mileage went back to normal.

Another recent decline caused a check engine code due to fuel being too rich. It was determined to be caused by a bad fuel pressure regulator. However, after this was replaced, the mileage hasn't gotten any better. I am currently getting 12 mpg.

Can anyone point me to any other causes of such poor fuel mileage performance?

[bryfry]

Do you still show a check engine light? A coolant temp. sensor out of range could also fatten the mixture up. Did you use an OE replacement for the regulator or did you go to Auto Zone and buy some knock off?

[ryankbruce]

Originally Posted by bryfry

Do you still show a check engine light? A coolant temp. sensor out of range could also fatten the mixture up. Did you use an OE replacement for the regulator or did you go to Auto Zone and buy some knock off?

No, I don't show a check engine light right now. The coolant temp has remained at constant levels throughout. In terms of the replacement for the regulator, I believe that the shop purchases their parts from NAPA so I figure it was an OEM and not a GM part.