I have had GMS1 for 3 weeks now.. I have no other mods besides the air box snorkel mod. Not that I care that much about gas mileage, but I found this odd. I reset my mpg often (every couple days) and have watched it closely the entire time. I drive the same amount and path each week, mostly highway.

Stock I got around 24.4 mpg average. Right after GMS1 I got about 25.6 average, even with ripping around the first week testing it out, it just seemed to keep going up. I thought, sweet! The last 2 weeks it has gradually gone down, I am getting 22.1 at the moment. If anything I have been driving less aggressively.


I can not account for this drop.. I have three assumptions.

(1.) Driving less aggressively on GMS1 actually yields worse mpg.

(2.) Recent colder temps closer to freezing and below have affected mpg. I haven't done much research on temp and mpg, but I assume it wouldn't hurt it, never noticed any diff on my other cars. If anything cooler should be better because air is denser. But what do I know.

(3.) GMS1 actually does slightly kill gas mileage over time and the initial gain is only the computer re-learning.

 

Another factor this time of year is the refineries change the gasoline to a winter formulation for a lot of areas and you will get worse gas mileage on it as well as the colder weather dragging it down. I've lost 1 mpg on the avg in the last month, same commute.

 

yep Iam is right .. the octane level in winter gas drops because there are additives added to the fuel to prevent gas lines freezing and such. Cold temperature definately makes your car run different as well.

 

Winter gas and much colder temps over the last couple weeks will do that. I've lost about 1 mpg too because a cold engine gets terrible mileage until its fully warmed up. Its pretty much this way for every car so you must have noticed this with other cars.

Also you need to get a longer sample for more accurate results.

 

Wow never knew gas changed with season, interesting....

I know I need much longer periods of time to be accurate, many factors are involved, but the differences have been pretty dramatic after the 6 months of observing. Gms1, gas change, and temp change altered my variables slightly.. I drove my ss/sc for three winters and I never noticed any difference that I remember, and I usually added mods every spring.. But just because I don't remember doesn't meant here wasn't a change... my heavily modded ss/sc got 27mpg avg though =/

 

I'd say it's the colder, denser air and the winter blend of gasoline. Nothing to be concerned about.

 

Yes, winter fuels roll out at different times across the U.S. They're formulated to burn easier (turn to vapor at lower temps), and generally make you get lower fuel economy.

Also, if I recall correctly, cold air also makes you get worse fuel economy. When the vehicle controls air fuel ratio, it does it in terms of mass, not volume. So in colder months, air is more dense, and therefore you get more air mass into the engine (even though volume is the same as before). Since the vehicle tries to keep the air fuel mass ratio constant, it'll have to inject more gas to get the desired A/F ratio. So you burn more gas, lowering fuel economy. On the flip side though, you use more gas, and therefore get more power.

I too have noticed a drop in F.E. since getting the GM upgrade. However I live in Michigan, we switched to winter fuels in mid November I think. I've also been letting my car warmup for ~10 mins before I drive it because I hate being cold :-p. Coupled with the fact that I find myself driving more spiritedly with the kit installed, I'm not totally surprised my F.E. is lower.

I'm waiting to see if it'll go up next spring...I was pretty consistent averaging high 28 to low 29mpgs since I do almost all highway driving. I'd like to see if I'll get closer to 30 or so once it warms up, with the kit installed.

 

it's normal to get lower mileage in winter.

 

How fast are you driving on the hwy? If your keeping up with traffic on 696, 275 ot 75 I don't undertdand how you are getting 28-29 mpg. Last winter I did a test and I tried to stay out of boost s much as possible, mostly hwy driving at 65mphy and I averaged 28.5 mpg.

 

I can get around that doing 80 on the highway in the summer. Drops about 2 in the winter though.

Don't forget to check your tire pressure. Cold temps drop the pressure which also lowers your mileage.

 

When i had my car hptuned with all my bolt ons i noticed that i get a few more mpgs on the highway now.

 

[QUOTE=ssilver;4505200]

(2.) Recent colder temps closer to freezing and below have affected mpg. I haven't done much research on temp and mpg, but I assume it wouldn't hurt it, never noticed any diff on my other cars. If anything cooler should be better because air is denser. But what do I know.

This. Cold weather affects every single system on the car and reduces fuel economy for many reasons, especially on startup until the engine is at normal operating temperature.

Absolutely true.

Wait till summer time rolls around, you will probably notice a big increase in mpg, I would estimate 5 mpg.

 

Going with the faster traffic...between 70 and 80mph on 96 and 275. I'm driving west in the morning and east at night, so it's with the low flow side of traffic, and slightly before rush hour, so it's almost always smooth sailing.

I'm seeing almost a 3mpg drop right now, from high 28's or 29, down to about 26 even.