Weird mpg fluctuations

[Tickle]

I recently updated my tune with an email tune from Don LaSota about 2 months ago. Before the tune and up to about 4 tanks of gas ago, I couldn't get better than 15.5-16 mpg.

The last 3 tanks have averaged 19>15.4>18.5. It's been varying before that but I didn't think much of it.

My driving habits haven't changed, I like to get on it from time to time, but not too much.

Any ideas? It seems weird to me.

 

[mwolson]

Spark advance around 2K RPM has a big effect on MPG. It is probable that he advanced your spark around that RPM range and it is netting you a little better fuel economy.

 

[Prototype007]

Spark advance around 2K RPM has a big effect on MPG. It is probable that he advanced your spark around that RPM range and it is netting you a little better fuel economy.

This and also the type of fuel you're running. If it's been cut with any type of ethanol, fuel economy will decrease.