I recently reset my battery in order to attempt to resolve a CD player issue. Since the reset, I've noticed a significant decline in my fuel consumption. I will admit that I do 100% city driving with plenty of traffic, but this has always been my driving style. I'm just trying to figure out if this mileage decline is just coincidental to disconnecting my battery, or something else that occurs to the car's computer system with regards to fuel consumption. I've never gotten great mileage in city driving, but since the battery disconnect, this is about 2 mpg less.. I'm getting around 12mpg where before I could get 14+. Again..100% City driving. Thanks all.

 

Hello,

It would be helpful if you can perform a fuel consumption test and compare it to the EPA estimate that can be found here. The test is pretty simple - fill the tank to the brim, reset the odometer and go for a highway journey until at least half of the tank is gone, then fill back up and calculate your average MPG. Highway will provide a long smooth road that won't add variables to the test, the longer you go, the more accurate the number would be, since you are increasing a sample size.

At least in the olden days, disconnecting the battery would reset the ECU, aka all the codes, presets and driving habits that it learned over a certain period of time. Since LS wasn't really designed to live in the city the entire time, factory presets likely don't correlate well with your driving scenario, so it will take a bit of time for the ECU to relearn the driving patterns that it has to deal with, and the MPG will return to its usual parameters that you come to expect after some time.

Hope this helps and best of luck!

 

The battery reset will have made the ECU lose all of it's "learning" of how you drive so it will need to re-learn all that.
Chances are if you check it again in a weeks time it will be back where it was, but even then if you were looking at average vs instant, then that average is over a tankful (or since last reset).
If you mostly city drive and you need better mileage then you will need to consider other vehicles.
The LS is good for a 4.3 liter V8, but economical she ain't.

 

An alternative fuel consumption test, without burning a half tank of gas as per post 2, would be to drive on level ground at a steady speed between 45-50 mph for a mile or so, no wind, and get a good reading from the display on what your current fuel consumption is. Repeat the test a few times and average the result. A healthy LS430 will get around 30 maybe a little more under these conditions (at least mine does and I get pretty good fuel economy, relatively speaking). If you are in the mid-20s time to investigate further. Boca's bad mpg could be local ambient conditions, too aggressive a driving style. caught too many red lights on short trips (makes a huge difference) or as stated above the ECU is still in a learning mode. Make sure your tires are inflated to spec and have clean filters and a clean MAF sensor.

 

I got the same results as OP. I have a 2004 LS 430 with 180k miles. I disconnected the battery when I got a new Denso MAFS from Rockauto and a new air filter and got an oil change and noticed my mpg go down as well.