C5 poor mpg

[Warren]

I just bought 1998 C5 installed
*new plugs
*new wires
*new fuel filter & pcv
*new battery
*Dynotune gained 47hp went from270rwhp to 317rwhp
problem is now the most I can get is 21mpg Highway
most of my driving is distance. Is there anything I can do?:hmm:

[needmorepwr]

did it get better mileage before the tune? I assume its an automatic?

[Warren]

It got better mileage before the tune and its a six speed it got 27mpg before the tune

[ss~zoso~ss]

hmmm, thats a stumper

[MadSeason]

Any way to check if you're running rich?

[Warren]

It was running rich, but the tune took care of that. Im new to vettes, how many miles would I have to travel in orderfor the computer to register higher mpg. 50 100 150 200.I ride 66miles to work at 60-70mph still get 21 at best

[Chad711]

21 at best is great IMO. I can never get over 16 mpg in my car. But I don't use 5th or 6th all that much either, lol.

I also have a pretty rich tune on my car. I think 21 mpg is pretty good man. You are not really to far from avg any way.

[Chirodan]

I wonder about that.... I know my Z06 is a little different, but I get around 30 mpg at 70 mph on trips... I am currently traveling about 80 miles a day round trip between home and work locations and still get about 375 miles per tank between city and hwy usage.
Don't know what it would be, but hopefully the pcm just has to readjust???

Danny

[Warren]

Im going to clean my air filter maybe that will help gain that elusive 28mpg

[Threed]

I got 27 best before my H/C headers install. After the tune I'm now getting 31 Hwy if I'm trying. Go figure...:yup:

[jdec]

That's a strange one. I drive my vette everyday and most of the driving is in town. I get anywhere from 20 to 23 in town and still pull down 28 to 30 on the hill and curve filled ozark roads. Good luck figuring this one out.:dunno: :beer:

[Bombguy99Z28]

Who tuned it? ;)

Most 'dyno tunes' tune for WOT only, and sometimes the adjustments they make to get your car where they want it at WOT end up compromising part thottle.

Do you have a unported, screened MAF? Sometimes running a ported MAF will bump your fuels trims to the moon.

Have you checked your tire pressures lately? Low tire pressure can lead to substantially lower fuel economy.

Do you have access to any data logging software?

It should definately be higher than that, I get 19-21 driving 60/40 city/highway (with a bit of 'playtime' mixed in), about 29-31 on straight highway driving, all based off tank fillups and not the dash. My speedometer is 100% spot on. My dash gauge for some reason reads about 1mpg high.

[Warren]

:shots: The Vette Doctors dynotuned the car. I gained almost 50 rwhp
from270 to317 The fellow I bought the car from installed a recalibrated mat
sensor. Last night from NY to Middletown aprox 70 miles aprox 21.4 mpg @65mph. She does have 124,000 on her.

[Bombguy99Z28]

I'd toss a scanner on it. I get the above mileage with 90k on the clock.

[Corvettestripes]

ttt

[9secondsflat]

your mpg should not drop that much unless your always 100% on the gas... with a correct tune your car becomes more efficient than stock.

[crawlingt]

maybe disconnect your ground and let the comp reset itself?

Just an idea

[Groucho]

:shots: The Vette Doctors dynotuned the car. I gained almost 50 rwhp
from270 to317 The fellow I bought the car from installed a recalibrated mat
sensor. Last night from NY to Middletown aprox 70 miles aprox 21.4 mpg @65mph. She does have 124,000 on her.


Reset the D.I.C.
I get 27 or 28 always in the summer...but 23 or so in the cold...

[tsts]

I'm sure you got an excellent tune from the vette doctors, they have a very good reputation for their work. There is another approach you may want to consider, "street tuning" where your engine is tuned and checked for many variables and performance setting while actually being driven. I had Chuck at Corvettes of Westchester tune my '99 LS1, A4 and the difference was awsome. I would guess the Vette Doctors can do the same type of tuning and are good at it, there are soooo many things they can change for better street performance through all types of driving. Also, If you have a forced air system (I think its called varamm or something like that) the car isn't moving when its on the dyno so its not working for you at that time. (if you got a stock air filter - disregard the last comment, but make sure you air filter is clean). Good Luck.

[ss~zoso~ss]

i averaged 32 MPG with my M6 camaro (only highway driving)

[JattGunMan]

i just my 2001 camaro ss and im averging about 18 mpg with both city and highway combined that doesnt seem right for a car with only 34000 miles on it?or is that what i should expect*mods are light and air filter is clean

[JTE]

Have you checked for codes? It could be something simple like the MAP sensor unplugged at the back of the intake manifold.

[powermad]

With cam and LT headers I get around 30 MPG highway. I think something is definately wrong. Are you getting the 21 on the average MPG or the instant??

[310stanger]

with a double overdrive 6spd vettes tend to get very good mileage sometimes 30 mpg. but i would say anything in the 20s is fantastic. if you gained 47 horses your gonna prolly lose a few mpg. chances are your also putting your foot in it more. thats a pretty sizeable increase. now why in the world are you worried about gas mileage in a vette? drive it like ya stole it.

[Warren]

I thank you for your comments, when I think about it 21-23 is not bad for a vette. I did'nt buy the car to perform like a hybrid.