Bad gas milage

Hello, my 2007 Buick Lucerne CXL w/V8 is getting less than 19miles per gallon AVG. Its seems the fuel consumption is getting worse. The on board cpu reads 17.4gph avg. I only use high octane fuel and I drive at a moderate rate. I do change oil every 5000 miles using mobil 5000 non synthetic Anyone have this problem? also every once and a while i do get that hard shift that sometimes.

Your car is rated, 15 city/23 hwy/18 combined.......exactly how much of a drop have you seen? What was it getting before it started to lose mileage?

While the onboard CPU is nice, best way to check is fill it up, note the mileage, go about 300 miles fill up again.....divide the mileage driven since last fillup by the number of gallons from the second fillup.....a lot of stop/go, local driving drops your mileage significantly, compared to highway driving....

Your vehicle is going on 7 years old.....what is the mileage? has the vehicle had a complete tuneup yet? Not sure if this has an external fuel filter or if it is part of the fuel pump.....

Have you checked for codes? Some tranny codes do not turn on the CE light right away, and will cause the PCM to run at full line pressure, which causes harsh shifts.....

Your car is rated, 15 city/23 hwy/18 combined.......exactly how much of a drop have you seen? What was it getting before it started to lose mileage?

While the onboard CPU is nice, best way to check is fill it up, note the mileage, go about 300 miles fill up again.....divide the mileage driven since last fillup by the number of gallons from the second fillup.....a lot of stop/go, local driving drops your mileage significantly, compared to highway driving....

Your vehicle is going on 7 years old.....what is the mileage? has the vehicle had a complete tuneup yet? Not sure if this has an external fuel filter or if it is part of the fuel pump.....

Have you checked for codes? Some tranny codes do not turn on the CE light right away, and will cause the PCM to run at full line pressure, which causes harsh shifts.....


Thx for your reply, I realized after posting, that it is hotter outside here in TX than when i purchased the car. That explains the drop in miles per gallon LOL! The car has 81000 miles on it and has been maintained well. I am sure it has a fuel filter on pump bieng 2007 model. The transmission only rarely shifts hard, I am thinking of having a local dealership change the tran. fluid. The car is driving and shifting fine 90% of the time. Due to higher tech tran fluid, i hope changing the tran. fluid is acceptable. any thoughts on weather or not to change tran. fluid? I do use this vehical to tow a 16ft bass boat! FYI i bought the car with 60000 miles on it in south west texas
and the A/C seats dont work i have checked the fuses not blown