Wow touch me the mastery of the mustang. 80mpg with a mustang GT!!

 

I just did a 450 mile trip mostly highway and got 25.8 miles per gallon in a GT. Around town and back and forth to work (only 10 miles form home) I normaly get between 15 and 18 and I'm not light on the gas.

 

Okay 5 pages, and 82 posts later, he still is having issues. Sooooo, here's kinda a long winded question, suggestion mix of sorts. Looking at it from the engine's point of view.

I'm a Mustang GT. I'm a performance oriented kinda machine. But I'm, a new 3 valve. I have this great computer attached to me that let's me try to figure out your driving habits, and adjust to my peak, accordingly. I am not, at least in the bone stock sense, a high compression machine. I do not require a top shelf liquid libation, but don't feed me brand x, either. Just because I have this throttle lag at moments, it's not my fault, nor what you have been feeding me, it's this dang drive by wire thingy they outfitted me with. Sooooooo, in answer to your question about my mileage, we have to look at your habits.Thank you for thinking kindly and serving me the best 93+ Sunoco you could find. But it has been a long time, and I have adjusted my computer's to try and accept it. I have retarded my ignition so much, but I still can't burn it all. Now you switch me to 87 and expect me to just immediately comply. Hey, for some 3000 miles you have had me adjust to what my builder said I would not have to do. But I did. Just for you. Sooo, help me out here. please adjust and advance the ignition for me. Right now, just as before, when you gave me that top shelf fluids you were reducing my power and pushing excessive fuel out my tailpipe, you didn't retard my ignition so I wouldn't fire off prematurely. So I had to have my computer adapt. Now you give me the proper fluids by lowering the octane level so my fuel can ignite when it is suppose to thereby allowing for a greater amount of burn, yeilding more power and better mileage. Soo, help me out here. advance my ignition firing back to what it should be. Check my injector's, my timing, reflash my computer after you do that. Then we can work together for the performance I should be able to provide you. When we are finally together on this, and you have me back to my optimum level, then we can talk about a little more air in and out of my system, with a new tune to make it right also.
Thanks for listening.

 

Nice perspective!

The 4.6 3V isn't ultra high compression, but 9.8:1 is still a bit high compared to the 9:1 and 9.4:1 a few years ago (nothing like 11-13:1 in the Japanese V6s).

The computer doesn't adapt the timing tables to the octane. it has a knock sensor spark adder table that adds X amount of spark depending on load and RPM if it does not detect detonation. If there is detonation, there is a spark subtraction table that pulls Y amount of spark depending on load and RPM. There's a ramping rate as well, so X or Y spark doesn't get "added" immediately.

I use nothing but 87 octane in my cars and haven't run into low gas mileage issues. In fact, I find the opposite to occur with high octane gas. I used to run 93/94 octane in my Crown Vic, resulting in 10-11 mpg!!!

The adaptive fuel table is about the only thing that is really adaptive, and it is used mainly to compensate for slight changes in the A/F ratio but doesn't do anything drastic. As long as the MAF/airbox air transfer function is spot-on, it will make minor tweaks.

My first fill-up was 14.7 mpg using 87 octane in mostly stop-n-go driving conditions, so there is room for improvement once the powertrain/drivetrain is broken in
.

 

thanks. The only problem I have with the knock sensor's is they don't recognize premature burn's only lagging ones, which a lesser octane, or bad fuel would provide. I think another aspect also in this scenerio he has before him, is that the long usage of the higher octane rating also added synthetic additives which make the higher levels burn cleaner to supposedly reduce carbon deposits in the combustion chambers themselfs. I think the stock fuel map should have enough margin tuned into it that there would be no long term catastrophic damage by using the wrong octane. I believe it is correctable. And I wholeheartedly agree about the lesser milage you had with your Crown Vic. My T-Bird is the same way.

 

I noticed in hot weather when accellerating from a crawl I will here a ping or two then it nearly instantly adjusts. I now use 89 so even a bad batch meets minimum requirements. I'm at 1700 miles now and its gettin a little better mpg every time. The local stations have also stopped with the winter mix recently.

 

If I accelerate from anything under 1000-1200 RPM, I will hear a lot of "marbles" rattling. I think it is just the gearbox but everything sounds new and different with the 4.6L 3V and the TR-3650.