Battery Disconnect

[jay in nb]

So Monday of last week I put in new plugs and air filter thinking that MPG would change a bit and better then the 13MPG I was getting, I drove until last Friday and no changes at all. While packing up for a weekend trip last friday I remembered reading that disconnecting the battery would reset the computer and by doing so MPG would change. So while packing I disconnected the negative for 20 minutes or so, hooked it up again and off I went. I seen a change, HWY over 16 MPG and city now over 14 almost 15MPG depending on my foot. I'm not sure disconnecting is what made the change but if so it was worth the minute it took to disconnect and connect.

[Sal-XK]

You dumped the computer putting it back in learn mode causing it to learn the new parts you installed..

[NeilSmith]

are you using the display to determine the mpg ? I never do. First of all its not correct because of the larger tires, and then Id rather just do the math instead of relying on a computer display.

[Sal-XK]

The computer display and your math would be corrupt because the odometer mileage is off do to the tires correct?

[Matt]

I use my display.

First off its not thrown off any more or less than the odometer is by tires.... and you're using the odometer to determine miles right?
Second, the engines computer is MUCH more accurate at determining the relationship between fuel consumed and miles driven. The resolution for fuel consumption in the engine is very refined..... however the "trigger" for gas stations are not. Just because you fill up and the gas pump turns off at 16.56 gallons does not mean that you have used 16.56 gallons. So dividing "miles driven" by amount to fill up is actually much more inaccurate. Some gas pumps are more sensitive than others so they'll stop sooner and therefore your "calculated" MPG will be higher than actual.

The computer however is very consistent and there gives the best tank-to-tank comparison of gas mileage changes.

That's how I look at it anyways.

[Matt]

You can easily adjust for new tire sizes by taking the MPG (calculated or computer) and multiply it by (new tire diameter / old tire diameter).

[NeilSmith]

i dont use the odometer neither, i use gps.

[Sal-XK]

i dont use the odometer neither, i use gps.

I used the GPS to get my spedo error so I can responsibly get some what of an accurate MPG. I'm running about 14.2 right now country hilly driving.

[NeilSmith]

it just sounds funny to me that if the computer knew what it was doing then it would automatically detect that you changed the plugs and you wouldnt have to unhook the battery to reset the system. im old fashioned , i guess.

[Matt]

i dont use the odometer neither, i use gps.

GPS doesn't account for altitude changes. If you live in a flat area it's not bad.

it just sounds funny to me that if the computer knew what it was doing then it would automatically detect that you changed the plugs and you wouldnt have to unhook the battery to reset the system. im old fashioned , i guess.

The computer doesn't detect spark plug changes at all, not even unhooked. That just puts the computer back in to "learn" mode all over again and resets all of the sensors. If there are any changes that computer should make due to the plug change then it would eventually optimize itself, but it will take some time... you just force it to do it sooner by disconnecting the battery.