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Discussion Starter #1
04 Mustang GT. Bought car 4 years ago from a Ford dealer. Was told car had a 91 octane tune? Car is an automatic and shifts very hard through all gears and runs great, so I figured it probably did, and I've always ran premium fuel and never had any problems with car.
Now 4 years later I've added typical add on's and it still runs great, but now I'M thinking about going with 4:10 gears.
Can a local speed/dyno shop hook computer to my car and make changes to keep speedometer correct? Or will I have to buy tuner to make my own changes?
Is there anyway I can tell if I have a tune already in my car using scanner? I hate to buy a tuner, then have to pay to have computer re-flashed to stock before I can make changes.
 

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Lorraine's driver
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I'm not sure, but you could check to see if the computer is chipped externally. It would be plugged into the computer, so you could just unplug it and the computer will be on the stock tune without it. Pull the passenger side kick panel and take a look. I think I had disconnect mine to see it though, but I can't remember for sure on that.

Might look like one of these...
chip.jpg

My Mach 1 had one of these for the 3.73 gears it had when I bought it. I ended up buying an SCT handheld tuner so I could make changes in the future without having to get a new tune, like different sized tires etc.
 

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When I got my 00 it was chipped externally. Yet another thing I found on this car that the jackasses before me did to it... if its externally chipped its a simple matter of just removing the chip. If the ECU is flashed and you don't have the tuner then yes you will have to get it flashed back to stock. Or just buy another ECU and when you install it with your own new tune load a tune with no PATS onto it.

Or if you are just doing speedo gears and its running great now then you can just do a speedcal for the gears and not touch the computer.

And also... as far as running great. I hope there is a wideband on the car if you have a tune or possibly a tune on it. No wideband=you have 0 clue if its ACTUALLY running well or running on the ragged edge of too lean or too rich. Floor the car and AF should snap to mid 12s and stay there through redline.
 

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Discussion Starter #4
Thanks for reply's I'll check for chip. I'll also check the AF to see what it's doing.
 

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I'm not sure, but you could check to see if the computer is chipped externally. It would be plugged into the computer, so you could just unplug it and the computer will be on the stock tune without it. Pull the passenger side kick panel and take a look. I think I had disconnect mine to see it though, but I can't remember for sure on that.

Might look like one of these...
View attachment 258449

My Mach 1 had one of these for the 3.73 gears it had when I bought it. I ended up buying an SCT handheld tuner so I could make changes in the future without having to get a new tune, like different sized tires etc.
I m about to get bigger tires then stock, will I need to adjust it using an sct tuner?

Sent from my SM-G970U using Mustang Evolution mobile app
 

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You won't have to but you should to get accurate readings. If you have a tuner you can do it with that.
 

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Discussion Starter #7
Well I went to local speed shop today and I was told they would be able to make changes to my computer for gear changes as well as tweak setting for other stuff I've added--no matter what tune is already in car--if any. And cost would be half of buying a new tuner.
 

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Lorraine's driver
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Well I went to local speed shop today and I was told they would be able to make changes to my computer for gear changes as well as tweak setting for other stuff I've added--no matter what tune is already in car--if any. And cost would be half of buying a new tuner.
Good news!
 

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Discussion Starter #9
I'll update thread as I go, but after sleeping on it last night, I'm having second thoughts on going to 4:10 gears! I enjoy taking road trips in car, and got to thinking about running 3000 Rpm's all the time
 

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I'll update thread as I go, but after sleeping on it last night, I'm having second thoughts on going to 4:10 gears! I enjoy taking road trips in car, and got to thinking about running 3000 Rpm's all the time
I have 3.73 gears and they are not bad on the highway

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I'll update thread as I go, but after sleeping on it last night, I'm having second thoughts on going to 4:10 gears! I enjoy taking road trips in car, and got to thinking about running 3000 Rpm's all the time
You have an 04 so you have a .62 overdrive. Throw some taller tires on there like 26.7 and that gear and 4.10s will not be bad for the highway. Think 75mph at like 2400 or so. Don't fear the gear.

That being said, lower gears are def nice for the highway. I live in Spain where we have German style super thick super well maintained highways (EU funding) and cruise speed here is 80-100mph depending on how quick you need to be there so I kept my 3.27s. 4V swap does help in that regard...
 

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Discussion Starter #12 (Edited)
I just bought new staggered wheels and tires a few months ago, 315 x 35x 17's. So hopefully it will be awhile before I change rear tires. Thanks for the idea's though.
Drove over 200 miles yesterday on back roads and had a great time, just turned overdrive off when not on major highways and had lots of power to play with (for a new edge mustang)
 

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Oh you have an auto, that means you have a .70 overdrive. Derp... yeah it'll spin a bit on the highway with the 25.7" tall tires, that OD and 4.10s but they really do help the automatic out especially if you put in a better converter.

The other good news is that the 04 auto was THE BEST automatic Ford put in a Mustang until the 2011 Coyote. Think of them as a factory "built" transmission.
 
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