maniacmikey

You can reset the trip computer to make sure you are getting the correct mileage figures on your car. I discovered I was getting 28 on the highway after setting it to zero before getting on the freeway.

ski

Possibly, but if he drives like a "grandmother", then the chance of pinging occurring is greatly reduced.If it does happen, then in his caseit's going to be at POT,the ECU will pull timing due to the signal being fed to itfrom the knock sensors, and thusany pingingwill be only momentary. Also, he may not know what pinging sounds like. And even if he does, then music from the stereo, andwind noise(especially in a vert)can easily drown outany pinging sound. That's why I suggested listening for pinging at WOT with the windows and top(forgot this in my 1st post, but I'm sure he knew what I meant)up, and the stereo and fan off.

Again, if he drives like a "grandmother", then the possibilityof engine damageis extremely minimal if he uses 87 octane gas with a 93octanetune.

Perhaps the dealer drove it like a "grandmother" too.

ski

Your car has a stock 3.55 gear. So that's not the cause of your poor highway gas mileage.
BTW, do you drive on the highway with the top down?

BigDish

I've driven on the highway with both the top up and down, I can't say I've seen a significant amount of difference either way.
I am aware that the message center items reset and generally reset them every time I fill up.

LL88

I get 15.6 in my sixer around town.....

emt4fire1951

Wow, you got somethin wrong. We just got back from a concert in Lake Tahoe NV. 400 miles one way. On the way up avg. 85 with short runs of 100 on hwy 5 (dude! thats the flow of traffic) and filled up in Stockton. 22.5 mpg. From there to Tahoe was 2 lane curvy on and off throttle. Hooked up with a red Z06 part way and every 4 miles at the passing lanes was a drag race to pass cars. Yeah it pulled me but not that bad. 100 or so. 8000 ft summit 6500 ft in Tahoe. Back to Stockton Monday and refilled. 21.5 mpg. I've never got below 18 around town jackrabbit starts (love to hear those Mac's) and the wife drives like a maniac to and from work. Have got as high as 26mpg at80 on long stretch of highway through the Mojave.
Sam

VaporDude

I have 2 05 Mustang GT's. One has a 87 octane tune and it gets 25-26 all highway at 70-80. This is the wifes car. The other one gets 23-24 mostly all highway 70-80 and it has the 91 octane tune. Yes 91 since that is what is mostly available in my area. She has the factory exhaust and I have the SLP LM. She has stock 17" wheels and I have 18x9 bullets. My foot is a little heavier than hers because it is bigger.

I would get that car checked out. No Mustang GT should get that bad of gas mileage unless your pulling 350HP or more. Unless your foot is made of lead in non-stop stop and go traffic.