I'm running the Superchips Firefly and it really screws up the overhead MPG. The other day I was driving along and the low fuel light came on. Usually I don't let it get that low, but I was planning a trip into Missouri where the fuel was about 20 cents cheaper so I let it go.

I was driving home from work and thought to myself, "self, you'd better stop for some fuel before you get home." I punched the overhead to see how far I had until I ran out and it told me 35 miles. I don't know why I believed it, the MPG have been way off since I put the Firefly on. As soon I had punched the overhead back to the compass, the truck died and I coasted to the side of the road.

No big deal, I was only a couple of miles from the house. There was only one problem, it was 2:30 pm. Everyone I know that could help is gainfully employed and at work. My wife was able to get off work early and rescue me. I feel like a real dummy.

 

I'm still learning mine, but the other day it said DTE was 35, and I needed 2.5 gallons at 16 MPG. Pretty close that day. I usually only look at the trip, and base my fuel ups on that, and the needle. This time I too let the light come on. It came on 30 miles earlier.(Got to know if it works right?)
I've also found that the overhead is about 2 to 3 MPG off.

Glad you got home to remind people not to trust the Overhead.

 

i have had mine to 0km till empty for about 20km and stil made it to the station and left it runnin while i got the pump activated at the cardlock. I dont know but some times electronics can be wrong.

 

My overhead is off by 2-3 MPG. That thing is worthless.

 

I only use mine to get a general idea of how I'm doing between fillups. Mine's usually off about 1-3 mpg. If it's all highway it's off by about 1 mpg. All city, it can be way off.

 

My gauge decides when i fill up. When it starts bouncing on the peg it is getting pretty close to the time i need to fill up. That being said i am below the red right now.

 

i have ran my over head til 8 miles DTE. but i tend to watch my fuel pressure gauge at those numbers and you could see the pressure starting to drop down when giving it throttle. so if you have a fuel pressure gauge it helps to see when your starting to run out of fuel cause your pressure drops to 0.

 

Mine is usually off as well. Even though I can count on one hand how many time I have let my tank run under 1/4 tank. Knock on wood, I have never ran out of fuel. It was beaten into my head that if I have a 1/4 tank left than it was empty.

 

The overhead shows around 22 MPG. (I wish) Last I checked, I usually get around 15 city. I guess the Firefly must be throwing some bogus info to the ECM to make it calculate that high.