I was driving with 91Tune for a while and was averaging 29-30 at constant 70-75mph, taking same freeway everyday and reseting the mpg guage. I decided to switch to 89 to see if any difference in performance for one gas tank. Now my mpg has dropped to 27-28 cruising at 70mph. No change in performance, not noticeble. I want to see how many miles I can get out of this tank and will probably switch back to 91 since advanced timing improves mpg and I think I got my prove.
Anyone experimented with different tunes?

 

I've tried all of them.. 91 one pulls slightly harder than 87, but noticable enough to prove that it's not in my head.

When I fill my tank with 87 and check the computer, it can show anywhere between 300-320 miles until empty. With 89, around 300 miles until empty, and with 91, 270-300 miles until empty. I spend most of my time driving around the cities now, but as I start making weekend commutes to UCSD, maybe my MPG will see something over 20. Right now, I average 16MPG with a 91 tune.

 

I don't think you can look at total milage untill empty at fill up since it is base on previous mpg and such so when you filled it with 89 it showed what you got with 87 and so on.

 

That makes sense, and you can't really count on the computer anyway. I have to calculate my mileage the old fashioned way. I swear I'd be getting 30MPG driving down the highway after a reset. The second I stop at a light or a stop sign, it dips WAY low.

 

30mpg with 91tune? That makes sense. Try to downgrade to 87 at next feel up and reset the mpg counter as you get on the freeway going 70. Ofcourse there are other factors like which direction the wind is blowing that day and such but if you monitor same stretch of freeway every day at same speed, the result should be within .5-1 mpg. I was getting around 30mpg untill I switched to 89tune. I also lowered the temp. of the cooling fan from 200F to 190F so not sure if colling engine 10degree earlier decreases my mpg or not.

 

How did you get the message console?

 

What do you mean? Like the message that says "### miles until empty" ? Just keep cycling through info; it will show you a dinky graph of your fuel efficiency, your average MPG and MPH, and other stuff.

 

Thatstang: I find 30 mpg on a Mustang near impossible to believe. Are you doing your calculation the real way with basic math, or are you relying on the computer of the car?

 

Right, and I wasn't serious when I said 30MPH either. When I first got my K&N drop-in filter, I reset my computer I drove to San Diego (about 100miles). When I got there I had 24MPG, I was so stoked! Now I hardly ever see the 20s.

But, I was reading another thread in the general 05-07 discussion about higher octanes yielding less mileage. I'm not going to pretend I know a thing about either.

 

My car is bone stock. I've ran 87 and 91, based on the puter, my mileage didn't change. My average was 16.5 running 87 and 91. Most of it is city driving with very little highway. But the car did seem, I'll say it again, seem, to pull better with 91.