Shelby350Mike

The calc on my car claims I get 12 mpg's... and I know that isn't true. Plus, everytime it tells me I'm low on gas, with about an 8th of a tank left, my car only takes 9 gallons at most... Don't trust the computer all the time. Its only there as a guide I've come to realize.

MustangFirstCar

Exactly. My car actually gets around 14mpg, lol, but I know it is accurate because I calculate it myself.

Nuke

It almost sounds as if your onboard is calculating based on some inaccurate parameter such as gears or tire OD; things that can be changed with a hand-held tuner. Has a shop or anyone connected anything to your OBD port? In order for the onboard to suddenly begin indicating that much of a change in fuel mileage, either a sensor is malfunctioning or you have something REAL going on.

Hand calculate at each FILL-UP;

mileage at current fill-up - mileage at last fill-up
gallons added

kput

Something I've noticed a few times, is that the gauge will read incorrectly, and slowly make it's way back up to it's appropriate place.

For instance;
I replaced my fuel filter. Filled up my tank. And it read Empty. It slowly crept back up to full after driving.
I also sat and idled for about an hour. (Don't ask why..it involves a woman.)
I get in the driver's seat, and it tells me I'm on E, but I knew I had about a quarter tank.
And earlier tonight, I had a hard takeoff, and was pretty much going WOT 70% of the short drive I had and it again told me I was near E, but knew I had over a quarter tank.

The gas gauges on our cars have issues.

MustangFirstCar

I filled up the other day and went on a spirited drive out in the country. Within 20 minutes my fuel light came on. Course, I knew that that was bull, so I kept driving, albeit slower, and the gauge eventually came back up almost to full.

Nuke

Be sure your ignition is off when you fill the tank. None of this playing music for the other patrons "appreciation".

MustangFirstCar

You mean not everyone wants to hear me blasting Jethro Tull through the gas station?

Nuke

Besides folks like me wanting to bust your head, then your head UNIT (despite the fact that I grew up on Tull, specifically the Thick as a Brick album), it also affects the fuel gauge and the onboard calculations. There's something about it in either the OM or the shop manual; can't recall which...

MustangFirstCar

Well atleast it's good to know that you can appreciate real music, lol.

Nuke

Not meaning to go off topic, but my youngest son was a DJ at his college and used to "borrow" my CD's. It took me forever to get my collection back.