calbrit561

I just bought my vette a few months ago and have been noticing i am getting terrible gas mileage. The car is a 99 vert 6sp with 80k miles. Acording to the DIC i have been getting between 18-22 mpg. In reality i am getting 16-18 if i divide the miles driven by the gas consumed at each fill up. I recorded the best mpg so far yesterday at 18.2mpg about 260miles with 70% hwy driving and the rest normal city with no spirited driving. The tires are all at 35psi and i dont ever run with the AC on. Also the car is stock besides a zip tie mod intake.

Vetteman Jack

Could be something like a dirty air filter, bad plugs or wires, etc. And your tires should be set at 30 psi cold. Those are some things I would check out first.

rjwz28

Agreed, other than the tires... overfilling tires decreases rolling resistance (and can screw up wear, but that's not the topic here)

What fuel are you running? How does the car behave?

Jeff T.

I've noticed low mpg = more fun!

You can't drive it like you stole it and expect Corolla mileage...

rjwz28

I have a video that I took to show how my car sounds with the cam, headers, and titanium exhaust from outside and inside the car... when I rev it from inside the car, you can see the MPG on the DIC drop from 11.3 to 11.2

Granted, I had just fueled up and reset it, so that was the average between the gas station and my house, but amusing nonetheless

I've gotten 26mpg or so on longer drives, even with the mods

73Corvette

You may have bad 02 sensors... clean air filter, good clean cats, working 02 sensors, properly inflated tires, clean MAF sensor, good wires and plugs, clean properly functioning fuel injectors, and you should get optimal fuel mileage.

I would add some Sea foam to my next tank of fuel... clean the MAF, replace 02 sensors, plugs and wire, see if that helps.

Someone may offer help on how to test your 02 sensors..

1Willy1

could also be your gas gauge is gone funky, like mine.

I was about to start replacing 02 sensors and plugs and such and then realized the problem was actually my gas Gauge.

kabluie

Are you pulling any codes? I would start there. Also, are you leaking any gas. Do you smell gas as you slowly walk around the car? At 80K miles, you could be needing plugs and coil packs. Those are normally part of the 100K mileage check, but things happen. Pull the codes first and see what the car is complaining about.

73Corvette

stu12dozen

Retrieve the codes, Grasshopper.

c4cruiser

The gas gauge wouldn't be an issue as he has checked mileage the "old-fashion" way. Divide the miles driven between fill-ups by the number of gallons of gas shown on the pump meter.

It could be that the odometer is off slightly if the rear tires are not the correct size, but that shouldn't be a big variance in the computation.

Driving style especially with a manual trans can make a difference in mileage. Staying a little too long in a lower gear or up-shifting at a higher RPM can easily result in poor mileage over a period of time.

1Willy1

Yes but hes measuring the mileage driven based on the gas gauge going to E and hes thinking the tank is empty, which in my case and MANY MANY others that was not the case.

My gas gauge issue is creeping back up since I stopped using fuel treatment and that is exactly what happens, the gas gauge drops faster then it should and shows your empty when your really not, so its impossible to get an accurate reading of your mileage.

73Corvette

Doesn't matter where the gas gauge is... your dividing the number of gallons into the number of miles put on since last fill up. Gas gauge has nothing to do with it. Fill it up till the pump stops,,,drive, refill till gas pump stops... divide miles driven by gallons of gas pumped.
took 10 gallons to fill up, you drove 100 miles...10 mpg
The gauge could be reading wrong but, that doesn't matter.

stu12dozen

Wow! I must have missed the part where his fuel gauge is going to empty.

Distance (miles) divided by fuel used (gallons) = MPG

What part of that equation don't you understand?

calbrit561

No codes besides an hvac actuator.

calbrit561

I am shifting 1st 4th 6th at all times to try and get the best i can. Doing that i am getting 18.2

73Corvette

Stop lugging the thing and drive it like a sports car... shift point should be around 3 grand....drive that thing!

calbrit561

I meant i was doing that to try and figure out my optimal mpg. normally my shift points are in the 4k range around town

1Willy1

ahhhh, Ok fair enough, if hes keeping track of how much he burned by measuring how much he is re-fueling then yes , that's going to give him an accurate number, my bad.

I was just very confused by my gas gauge issue I thought maybe he could be dealing with the same thing, but I guess not.

shhhhhhh, stop chirping grasshopper.

73Corvette

Gotch ya...