Curly,

I will bet good money that 10% ethenol or not in the fuel is part of the reason. You will note that the tag on the pump states that it "MAY" contain 10% (or it may not!)

I also think that the car isn't all that aerodynamic so there is probabaly a huge diff in MPG vs road speeds. Now that we have been in town doing errands and such in mixed driving, I am getting more MPG in city /urban driving than we got on the highway....it's odd.

I too would love an explanation.

QuickRick

 

Ethanol certainly may be part of the reason. Sounds like a good topic for a new thread.
Why is the mileage worse in cold weather? Why is there no consistancy? Weather? Ethanol? A car performs better and makes more horsepower in cold weather so you would think it would get better mileage (have to use less throttle)
How much Ethanol is in the gas we use and how much does it hurt mileage?
What is the mileage difference in Winter and Summer blend gas?

Still my car can get different results on the same tank of gas?

We do not have any snow here in the United States of Texas but we have got some temps in the teens and twenties.

I am looking for some consistancy or I can never know for sure if my changes are improvements or not.

For instance I do not pay much attention to city mileage because there is too many variables. But my average mileage started at about 21 for a tank, then went to 23 with some of the mods and with exhaust it went to 25 MPG.
So in the last 9 months my city average went up 4 MPG and that is significant. Last tank went to 19 MPG and I do not have a clue why? I was thinking my mods were working and the BAM! I get 19 and do not know why. That was not a full tank and it is climbing.
I expect (Hope) that with the Trifecta tune and underdrive pulleys it will gain a little more.
The EPA ratings was 21/30 and that was very close to what I was getting when I got the car. Now I am about 25/35 and hope to end up with it about 28/40 when all of the mods are done.
I think that would probably be around the max for mechanical mods with out going to adding ugly aero tails on the back, wheel well covers or other hideous looking aeromods.

From there I can start doing some Hypermiling techniques and possibly improve the overall even more. Right now I am working on mechanical mods and for the most part it seems to be working but not as consistant as I think it should be.

 

Its possible you have other issues at hand.Maybe you have a sensor thats operating on the fringes,not enuf to kick off a light but enuf to vari the parameters.O2 sensors can do this.A vacuum leak can play games too,at certain temps may work good and others cause it to leak.Stupid things like voltage swings, you do have a lot of stereo .. coil output is dependant on voltage..(I wonder how these would run on a step up box,say 16v?)If this is something thats ALWAYS been happening then I'd look at everything.Otherwise if this started after a particular mod,backtrack and troubleshoot that mod.You said you changed tire size,was it recal'd after?The ECM may be trying to compensate and confusing itself. Its like a puter,go back to the last known stable state and work from there.

 

I just filled up and got the final mileage on that tank of gas. I had been getting 24 tp 26 in the city and this one was 21. It has been windy and cooler lately but 21 is not very good.