Hello, I have a 2006 5.7 1500. When I first got her I would average 10-15mpg around town, and 24 hwy. At some point, (I believe it was after the battery died but not for sure) the mpg reader started reading funny. Around town it reads from 15-26mpg and on the highway it reads 6-12. I mentioned this problem to my dad, who had me take my foot off the gas while driving. He said there is most certainly something wrong somewhere because when I take my foot off the gas the mpg continues to drop. He said the mpg should increase when my foot is off the gas but for some reason it is consuming more fuel. Any idea what is causing this? I did an oil change not very long ago, and replaced the oil and air filter. Thank you in advance for any suggestions!

 

First thing I would do is make sure of the mileage by hand calculating a tank or two of gas and it's not just the computer.

Also, if the battery died and the PCM reset, it takes a while for the computer to "re-learn" and may just clear up over the next 200-300 miles driven...

 

Thank you Hammerz71. I have done the calculations and the readings seem to be pretty close to what the gauge is reading :/ It's been well over 300 miles since the battery died, I'd say around 1500 or more miles. Any other thoughts or suggestions? Maybe the fuel filter?

 

Unless you're up over 100k miles on the original or the truck has been running really crappy no-name gas (remember, 87 octane is a big no-no on a Hemi) then I doubt it's the gas filter.


I'd be more inclined to think it'd be more of a general tune-up thing. Over 30k on copper plugs can start to sap fuel and believe it or not, as little as a 10 PSI low in tire air pressure can cost you 3-4 mpg.
Dirty throttle body and EGR are BIG TIME MPG killers. 30k on the EGR (50k tops) and throttle body should be cleaned at least every 30k.